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Newbie to Gas General Information

Old 05-01-2009, 12:05 PM
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Default RE: Newbie to Gas General Information

It's basically just the design of that particular engine, as there are several other reputable brands that use a single prop bolt/nut to hold the prop in place, and for engines of a much larger displacement than yours, such as the Zenoah G45 and G62. Using just the centre bolt/nut on your 26cc will be quite okay.

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Old 05-02-2009, 09:27 AM
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Default RE: Newbie to Gas General Information

I have a question about the fuel tank. My gas line is kind of rigid. The line that goes from the tank rubber stopper inside the tank (the one that picks up gas, with the clunk on it) is kind of rigid (not flexible enough). When I invert the tank it does not bend as it should. Therefore if I go inverted, it will be sucking air. I used a piece of the yellow fuel line. Is there something better (more flexible) one can use? Where can I get it?
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Old 05-02-2009, 03:43 PM
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Default RE: Newbie to Gas General Information

For all in tank plumbing when using NON ethanol blended gasoline I use the 3/32" or 1/8" Hayes black seamless neoprene tubing which is very flexible and never gets stiff with age. Always use a felt filter clunk and some sort of barbs arrangement on our brass tubing along with small tie straps to keep the tubing in place.

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Old 05-02-2009, 06:15 PM
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Default RE: Newbie to Gas General Information

This post: The original post was a Thank You that was removed by the Moderator Rcpilot . . . .

The following is a a copy of a post on 7-5-12 in the Syssa engine thread added by the moderator w8ye . . .

"Whatever you do, and however you do it, just keep in mind that the best ground tuned engine in the world will STILL very likely require some adjusting once airborne. Point being, don't get carried away with it (adjusting on the ground/test stand), and don't waste a lot of time on it when you could be flying. In the end all you're trying to do is get it running good enough to get it airborne?

With that in mind, my experience has been that a rich engine rarely quits. To that end, I leave both needles fat when adjusting on the ground - so unplanned glider practice is minimized? THEN, once airborne, you can fine tune with an educated guess on which way you need to go to get to optimum (usually a compromise you can live with, seldom perfect)."

The take with your point is that a rich engine rarely quits in the air. Many guys are setting up the low speed as lean as possible, looking for a smooth idle, concerned that it's going to "load up" - and that's biting them in the butt once airborne. That's not the plan when setting up a gasser. Properly set on idle that engine should actually be running kind of uneven, not hitting on every stroke? These engines are pretty capable of running rich without loading up to the point they'll get you in trouble because of it..... -Al
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Old 05-03-2009, 07:16 AM
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37. Throttle Linkage, Trim, and Adjustment - Our carbs are really intended to be nearly "full on" a majority of time...not to be continually varying them in the middle range which is our main usage. So, to get things "right", it's important (maybe VITAL) to properly setup the mechanical *and* electrical setups of the throttle and carb arms. Here's what I suggest:

Method A - Basic Approach

Full DOWN throttle trim is "cutoff", closing the carb completely. This is the full ATV adjusted on the bottom end. I set this by fine tuning the ATV so the control rod isn't binding the servo, but the throttle plate is completely closed.

Middle "detent" throttle trim is the "landing" and "taxi" trim setting. That is determined by a couple of things that inter-relate. First, in the System setup screen, set the Throttle trim authority to 50%. It is far too sensitive otherwise, for a gasser. Then, assuming that you've set the carb arm length to be slightly more than the servo control arm take off length, the 'half trim' should be where the plane will sit motionless when engine is fully warmed up. Finally, set the Throttle Curve function ONLY if you cannot get the low end sensitivity/linearity mechanically. Reason I suggest that is that the mechanical rotational and linear geometry of the arms can go a long way toward getting it "right".

Finally, the "full" trim is the "hot restart" setting, because my carbs tend to be leaner on the low end, so a hot restart needs just a bit more travel.

Method B - The Real Deal

Now - the "real deal" is to get the correct pushrod length. There are, again, many opinions on these mechanical setups, but I'll just describe mine, as it is consistent, repeatable, and reliable.

Use a Servo arm where the "take off" or "ball link attach" point is about 5/8" from center of shaft. Purpose of that distance is to ensure that you'll be close to needing 100% ATV on both ends of the throttle channel, making the "clicks" of throttle less profound. You don't want big differences per click, and a longer arm will be too much. Shorter arm requires too much ATV diddling, and introduces mechanical expo which may not be in the "correct" direction.

On the Carb, use an arm with the ball link take off point at 3/4" from shaft center. This permits more rotation of the arm, and helps solve sensitivity issues mechanically at the carb. Walbro carbs are HORRIFICALLY non linear and overly sensitive...

Now, with both arms installed, set your ATV to about 90% on both extremes. Open the carb arm to "FULL THROTTLE" (where it hits the mechanical full throttle stop), and move throttle stick to FULL throttle. Measure the straight line distance between the centers of the ball link attachment points. Now, go to full CUTOFF low throttle and low trim, and rotate the carb arm to FULL CUTOFF. Measure that straight line difference. If not the same as the full throttle length, take the average. Create a Carbon fiber, or stiff metal pushrod of EXACTLY that length.

Install. You will be very close to "perfect". Tweak the ATV end points as needed, you perhaps will need to adjust the Throttle trim authority again, but you will be very close to a good linear setup. If it isn't like you want it, THEN setup the Throttle curve function, but not until after all the mechanical stuff has been taken care of.

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Old 05-08-2009, 02:51 AM
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Default RE: Newbie to Gas General Information

Original:Frank C. Bowman
Check your reeds?
I installed a new Bowman ring in a DLE 30 rear intake engine for a friend. After installation compression doubled before starting engine so compression was already very good. With cowl off of plane and plane secured in blocks I turned prop over 1 turn to bring fuel up to carb. Fuel went 1/2 way up fuel line and dropped back toward tank. My friend had complained about low compression and that engine was very hard to start. I remover carb and plastic reed block from the engine to inspect. I noticed that both reeds were slightly open just a few thousandths. I removed the 2 screws that held reeds to see why reeds wouldn't lay flat against reed block. The plastic block is cast and reed surface is not flat for a good positive seal against plastic reeds. I taped down a piece of 320 grit sand paper to edge of flat table top to lap reed block surface down flat. Reed block has a lip where it mounts to carb so place sandpaper on the edge of flat surface with lip hanging over the edge. lap each of the sides down lightly until flat, it doesn't take very much to do. The holes on the 2 steel reed retainer plate are punched, not drilled. So file or hone the 2 plate bottoms flat and remove burrs. Place reeds back on plastic block and screw back in place but be careful as you can strip holes easily if you tighten too much. You can add a tiny bit of Locktite to make sure screws don't back out and go into engine. Make sure reeds are totally flat against reed block. If not remove reed and turn it over , often times one side of reed is flatter than the other. Upon doing this simple mod. I reinstalled card and tested the fuel draw problem. Upon turning prop 1 turn fuel now instantly was drawn up to carb and stayed there. My friend turned on the power switch, 1 flip by hand, engine started. We repeated the process with 1 flip each time about 10 to 12 times, engine started every time. Merry Christmas to all. Frank C. Bowman AKA Ringmaster
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Old 05-08-2009, 10:18 AM
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This is a READ ONLY thread. For those of you not familiar that means you can READ this thread and that is ALL. You may NOT post questions or comments in this thread.

If you have read this entire thread and you still have questions, please start your own thread in this forum and ask your questions there. DO NOT post questions in this thread. You may READ this thread but you may not post questions or general discussion in this thread.

The only people allowed to post in this thread are myself and Bob.

This thread has been given "Sticky" status because we see the same newbie questions over and over in this forum. Bob was kind enough to give freely of his time and put this thread together. Please be respectful enough to obey the rules and NOT post here.

Thank you.

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Old 08-10-2009, 04:08 PM
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38. Using Stuff NOT from the Manufacturer - in general, unless you have a field full of qualified and experienced gas-helpers, make your FIRST gasser install **exactly like the engine manufacturer tells you to do it*** This helps you in several ways....1) you'll be doing what the folks who will WARRANTY the thing have said to do....2) if you have to call them for help, they will know how your system is setup and it will be easier on both of you for troubleshooting....3) sometimes stuff that folks buy as 'add-ons' to make things better, easier, neater, really do NOT, and then as a new user, you have inadvertently placed unknown variables into the "why doesn't this work?" equation. It is just really easier, the FIRST time, to "do it the easy way", and "follow the instructions", as much as that advice may seem counter-intuitive to our knowledge and reason.

39. If you have read this thread this far, please go back to the start and remind yourself of the "basics". When things don't go well, most of us immediately begin jumping on "device or component failure". The sad truth, and I am absolutely including myself in this, is that the MAJORITY of time it's OUR failure to seek, read, and heed qualified guidance. We're just too proud since all of us have had chainsaws and weedeaters since we were kids. They "all work the same"...... NOT!!!!!!!!!
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Old 10-10-2009, 09:24 PM
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This is Quoted from a post in the gas forum Dated 4-13-11 w8ye

Original: Tired Old Man

Setting up a gas engine isn't really any more difficult than correctly setting up a glow engine. First order of business is never to build something while subscribing to the law of minimums, which so many of you do. In doing so you assure than the smallest thing can become the weakest link that can take down your plane. That may be battery type or capacity, hardware dimensionality, servo strength, whatever.

Next is to take the time to learn about the products you are using instead of accepting as gospel something you read on the Internet. It was on the Internet and therefore must be true, right? Yea, right. In learning about what you have, want, or plan to use you learn how to install and use it correctly. Learn about servo to throttle lever geometry. Learn about fasteners, connectors, and wire security. Learn about current consumption with the particular products intended for use. Size everything for a minimum of 25% greater than required. 30-50% is better.

For some reason many of you think glow engines are safe while gas engines are not, or that glow engines are safer than gas engines. I cannot understand that way of thinking. I can kill someone with a 1" blade pocket knife or a 16" blade butcher knife. A blade is a blade. People are reacting to gas engines out of fear. Apparently fear of the unknown, with the unknown being their lack of education and familiarity with the product. Others are responding to titillation from advertisers trying to make a of you.

The simpler the end result the more reliable it will be. Pretty basic thinking but it works. KISS is still a very functional method of doing things. In engineering if it doesn't break it hasn't been loaded enough or doesn't have enough features yet. It really does work that way but that doesn't mean it's right. Ignition kills fail and do so all the time. Failure to program your tx failsafe will bite you in the ***** long before a correctly set up engine will and that has been proven over and over. I've seen it too many times.

Buying more goodies to overcome a deficiency in knowledge and ability will not make anything safer. Just more expensive with a greater propensity for failure. Where is the problem in flying for 20 minutes to run out a gas tank? Worse, why did someone use such large gas tanks unless they originally intended to fly for that long? Didn't they bother to perform ground runs to see how long the tank would take to empty? Using too smAll of an ignition or receiver battery? Another area where the user wasn't very bright or was trying to cut cost corners. You read about them all the time in the 2.4 brown out/lost link threads.
Original:Tired Old Man 11-9-11 Selection of Gas Model Servos

A good servo is a good servo regardless of gear train composition. The use of metal geared servos is still only a relatively recent event. Say the last 7 years or so. Prior to that all the 35 and 40% planes were being flown at all the high dollar contests like the Tournament of Champions on nylon geared servos such at the JR 8411. Until about two years ago the Comp Arf manuals were still calling for the attachment of their servo arms to the nylon output wheels of high end servos. On a more personal level I generally make it a point to use JR 4711 servos for all my throttles. The 4711 is a nylon gear servo. One other point, many metal gear servos have a nylon idler gear to drive the output shaft from the servo motor, so they are not 100% metal gear.

Your selection of servos should not be based on price. If that is the qualifier for what servo you use in your aircraft you are betting the life of the plane and the safety of everything around when you are flying on the cheapest common denominator. You are effectively telling yourself you cannot afford to be flying the aircraft that you put the servos in. Speed, precision, accuracy, and durability are never found in the bottom dollar servos. My personal tests of the Power HD servos determined they would never find a home in my planes. The good stuff still costs more. Even your previous choice of the HS 645mg leaves a lot to be desired. They are strong enough for most small gassers but a lot of accuracy is left on the table. A lot. Ever wonder why your planes don't seem to the same things the same way every time?

So a good servo does not have to be metal geared but it does need to be accurate and dependable. As noted in the quote from Bliksem, correct set up is also extremely important. I've seen $130.00 servos destroyed on throttles because no attention was paid to linkage geometry. I've also seen servos literally burst into flames because of ganged servo bind. There have been servos that stripped the gears just from the weight of an aileron or elevator flexing during a semi hard landing. So pick a good servo and take the time to learn how to correctly set up linkage through proper geometry. A good nylon geared servo that is correctly set up will still work just fine if you did your job and installed things correctly. Learn to determine what speed and torque will be required in the worst case scenario and plan to meet that condition all the time. You would be surprised to learn how often that worst case condition is achieved and repeated.

Your plane wil only fly as good as the person flying it and the equipment in it. A great pilot can overcome some equipment deficiencies but he will never be able to fly up to his potential. The plane will not let him. An average pilot flying good equipment that is correctly set up becomes a great pilot a lot easier, and faster, when he is not fighting equipment deficiencies. I won't tell you what you should buy because you know what you need better than anyone, but I will say choose wisely and don't use cost as the primary qualifier. Those that do lose more planes and replace a lot of equipment a lot more frequently.

Original: MTK

BTW- I took last year's tank apart in which I had installed PolyUrethane tubing (Tygothane special formulation for gasoline). on the clunk line, McMaster Carr part #5549K44

As supple and strong as the day of installation. It is a clear tubing but it may come in various colors, I have not checked. Black would be perfect for inside or outside the tank but isn't really a big deal either way

Tubing is 1/8"ID x 1/32" wall, dirt cheap at 30 cents per foot. It comes in 25 foot lengths min plus shipping.

I will fly the same piece of tubing inside the tank this season to see if it will continue to perform as I want
This is from a post dated 8-7-11
original: Tired Old Man


20 flips to get a pop when an engine is choked tells me there are one or more things wrong with the set up. The first would be verification the choke plate is fully closed. The second would be the geometery of the throttle linkage arrangement. A third would be the positioning of the throttle stick and trim tab. That also takes things back to linkage. A fourth would be a leak in the plumbing, inside or outside of the tank. A fifth would be concerning the pulse port. Lastly would be the pump diaphragm and condition of the check valve flaps.

If the choke is fully closed with correct length linkage, with the linkage installed at the correct positions on the throttle servo and carb throttle lever, The throttle stick should fully close the throttle plate with the trim tab in the full closed position. Without moving the throttle stick, the trim tab should be able to open the throttle plate a good 1/8" open with only 1/2 to 3/4 rotation of the trim tab. If that's not happening the linkage set up is fooked up. The engine should be able to start and shut down using only the trim tab with the throttle stick at full close. If the throttle plate is not opening no fuel gets into the engine, ergo, a lot of flips to get a pop.

MOST people screw up the throttle linkage on a gas engine. I see it so often is grants me the ability to say "most". They relate linkage installation to what is done on a glow engine where a rod is slid into a throttle lever EZ connector, connect the other end to another EZ connector or clevis on the throttle servo, with the servo motion dialed back or forward to achieve rotational distances with travel adjust. Even a method similar to that assures absolutely horrid gas throttle response, along with lots of potential starting issues.


Linkage installation on a gas engine starts with the throttle stick and trim tab in their fully closed positions, the throttle servo and carb lever at their mid travel point positions, travel adjusts at 100%, and no other mixes or trims in that channel of the radio. From that point you establish linkage lengths based on attachment at the innermost point available at the servo, and outermost point available at the carb lever. You want maximum servo rotation to provide minimum lever movement, with minimal carb lever movement providing maximum travel motion. The carb end requires very little servo throw to achieve stop to stop travel so you dial down travel at the servo end by using inside attachment points. You do not dial down servo travel by using travel adjust when it can be avoided. That travel is your resolution, and without good resolution you have really bad throttle control. You see it all the time with people coming up with a multitude of ways to build throttle mixes to smooth out throttle response. That's too much work and takes too long to get right for me. The other side of that is seeing people with throttle servos that are binding up at both ends of travel.

It's quite acceptable to make new holes on the servo arm inside of those provided by the manufacturer. Those that do experience immediate benefits.
Original:Tired Old Man 8-24-11
Gasser Throttle Linkage Installation and Set Up

Servo selection:

Use a standard sized servo. That's the initial basis of a good throttle servo. If you want precision, speed, and accurate throttle position every time, use a good coreless or digital servo. If you don't care about a wandering throttle position or difficulty in establishing a consistent idle, an analog servo will do. Servo quality is predicated on the choice of manufacturer and price. The low end servos provide low end performance and a lot of frustration. They don't center well, if at all, and rarely hit the same position for the same stick input twice in a row. You will be the one to decide what you prefer. Servo torque should be a minimum of 48 ounce inches. There is no maximum but 48 to 50 oz. in. is plenty for any throttle servo. Micro servos are a very bad idea. The Hitec hs225mg is as small as I would ever consider for a throttle servo. Metal gears generally last longer than nylon gears, and carbonite gears are noted for breaking when used with a gas engine. Nothing lasts forever. That should be enough for you to make a servo decision.

To start a linkage installation, set both the throttle servo and the carb lever to 50% positions. So the carb is opened up half way and the servo is at midpoint. Use a clamp or other means to secure the carb lever in position. Remove and discard the idle stop screw that may be installed on the carb when new. That's used for yard equipment that are normally operated at two speeds, idle and wide open throttle. Hopefully you use a wider range of throttle positions than just those

DO NOT remove or disconnect the throttle return spring. It's on there for several reasons, all of them good for what you want to use the carb for. If you are using a servo of a size suitable to be a throttle servo you will never have a problem because of that spring. If you are using a servo unsuitable for a throttle servo all the problems you will have were self-induced. You know how to fix that. Get a more appropriate servo.

Before going any further determine that travel adjust for the throttle servo is set at 100% both directions, no trims have been input, idle trim tab on the transmitter is fully closed, no mixes are in the radio, no rates have been set, and use the shortest servo arm that came with the servo. You will use the innermost hole on the arm. You may find you will want to make a hole inside of that one for best resolution. You will want maximum servo throw to provide minimal linkage travel. That doesn't make sense now but it will later.

Measure the distance between the servo arm and the carb lever hole. That's your beginning linkage length. Make the linkage and install using your favorite and safe attachment method at both ends. I'll suggest that at least one end be a bolt on ball link, that no pinned clevises be used, and if a pinned clevis is used it will be a metal pin with a secondary method of securing the clevis. 4-40 ball links can be a pain because of size and screw heads. Dubro makes a 2-56 bolt on ball link for 4-40 threaded rod. I'll let you look up the part number No metal to metal contact is ever allowed, although it's perfectly acceptable to use a metal or carbon throttle rod as long as it's electrically isolated from any metal levers or servo arms with something like a ball link. Zee bends in a metal rod connected to the carb lever will be a disaster. Don't do that.

Hopefully the carb lever is at least 1" long. you may have to change or modify the throttle lever at the carb. There are bolt on products available to complete that task. It's better if it's 1-1/4" or so because you want use an outer hole (farther from the throttle plate rod center) to obtain maximum throw at the carb end. You want an installation where the servo moves a lot to move the throttle plate a little, with the total rotation of the servo being enough to obtain full range of motion at the carb. The short servo arm with the long carb arm helps you do that. That's resolution of the finest kind since it does not require mixing and expos. Starting to make a little sense now?

If using a decent servo you can check the amount of throw from one end to the other and how that impacts the carb lever without powering up the radio. You should be pretty close and need only to increase or decrease servo travel a few percentage points to go from full closed to full open. If it requires that you adjust travels more than about 15% in either direction move the attachment point at the carb lever in or out on the lever to determine the effects. The linkage may still be a little too long or short. Also work with adjusting the ball link/clevis in or out a little bit. This is where making a new hole on the inside of the servo arm becomes helpful.

Ultimately you want the throttle plate to achieve a fully closed position with the throttle stick full back and the trim tab full down. THIS is the absolutely correct throttle stop/engine shut off position of the carb throttle plate because it provides full control of the throttle for idle trim and engine shut down. It also makes establishing your idle positin extremely easy. Closing the plate will cut the engine every time. The trim tab will be what you will use to set idle throttle position. You can play with transmitter multiple idle positions later for those that like the idea of high and low idles. I don't but some do. if you let the engine warm up before setting the idle it will likely be the same when you land as it did when you took off. That's another subject of its own.

You do not want the servo or the carb level to EVER hit a hard stop at either end. The carb will be providing the engine the ability to make 100% power long befere the throttle plate is fully open. The throttle plate does little for power/RPM after it passes somewhere between 75% and 80% open. That has to do with the plate and rod dimensions/geometry and it's impact on throttle fraction area. Don't worry about this because I'm certainly not going to write all that is required to define it all.

If your servo is moving a little and the carb lever is moving a lot, the linkage geometery and installion is totally wrong. You will always have trouble with throttle sensitivity when things work that way. You want a little servo travel to make a little carb lever motion, and to be able to use 100% of the servo travel to achieve 95%-100% of the carb lever movement without hitting stops. It's ok to use 100% or a little more or less of the servo travel, but it is never ok to introduce so much travel or linkage so long that any bind will be present. That kills servos in a big hurry, and drains flight batteries.

Hopefully the above will get you off to a good start and make throttle linkage on a gasser a bit easier for you to set up. Copy and past this post into a Word or text document on your computer for future reference. I did

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Old 10-26-2010, 09:01 PM
Bob Pastorello
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40. After months of never having to address "oil ratio", it is time to do it here. The OIL you choose is not as important as the mixing ratio you use. You are GUARANTEEDfailure **if** you use crappy oil AND too lean a ratio. Or you will GUARANTEEfailure using the FINESToil you can find or buy ANDtoo lean a ratio. Oil lubricates the innards, keeps parts moving like they are supposed to, and helps dissipate heat. So here is "Bob's Newbie Gas Advice for OIL" 1. Contact the engine manufacturer to find out the ratio they recommend, AND read the manual. 2. Select an oil that is available in your area, not too exotic, and something you would trust your most expensive chain saw or weed eater to. 3. Mix the oil properly, and 4. Do NOTAdjust the engine too lean.EVER.
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Old 12-10-2010, 12:58 AM
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It was requested that I post this troubleshooting guide for Rcexl and many C&H ignitions here in this thread. If you have no spark or think you are having an ignition problem, carefully following this guide will test the ignition module, hall sensor,and spark plug cap components. This guide can be used for single or twin cylinderignitions,it does not test the manual or any optical ignition switches that may be in the system. You will need a good fully charged 4 cell Nicad or Nimh battery, an old servo extension, and your trusty volt meter. So,......

Take an old expendable servo extension and cut off the male plug end, separate the wires, strip a bit of insulation from each of the 3 leads and plug the other end into the sensor lead on the ignition module.

Puta goodsparkplug in the cap, doesn't need to be all the way seated but far enough for the hex of the plug to make good contact with the metal shellof the plug cap, plug a fully charged 4 cell battery directly into the ignition.

Test for battery voltage at the red and black wires of the test extension you made and plugged into the sensor lead of the module, if there is no voltage replace the module, if there is battery voltage->

Short the white and black wires together, every time you break this connection there should be a spark, no or intermittent spark=bad module, has good spark->

Remove the test lead and plug the sensor on the engine into the module and turn the engine over, no spark, replace the sensor, good spark->

Remove the spark plug, look down into the plug cap and turn the engine over, if you see spark arcing through the silicone boot to the metal shell, replace the spark plug cap, no visible spark but you hear a snap->

Put a small screw driver into the bottom of the cap, turn theengine over and you should observe spark jumping from the screw driver to the plug cap shell outside of the silicone boot, an arc of about 1/4"-3/8", if it does this there is nothing wrong with the ignition, if you hear an arc but it's not in the cap with the screw driver, it could be a problem with the
resistor in the cap or the high tension lead where it goes into the cap, replace the plug cap.

All of this can be done on a bench, the plug does not need to be grounded to the engine.

Good luck!

Wire connections for the RCEXL Ignition.

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Old 12-18-2010, 07:38 PM
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Thank you Jodi. [sm=thumbs_up.gif]
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Old 02-10-2011, 06:34 PM
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Default RE: Newbie to Gas General Information

The following was posted in the gas engines thread on 7-1-12


I've been contemplating lately how much help the use of a primer bulb on our planes could be, and how many problems it could solve, especially for newbies. I know, I don't really want one on my plane(s) either, but it does have some logic. When someone says "firing up your (weedeater, leaf blower, chainsaw)??" when you are using one on your plane, just tell them "Hey, at least my plane always runs!"

Here's the "argument". Most people don't have a clue about how a primer bulb system works, but it is pretty ingenious actually. It does not "push" fuel to the carb, and it does not "inject" fuel into the engine. What it does is draw fuel from the tank all the way into the regulator fuel chamber. It creates a suction that moves the regulator diaphragm open, which opens the inlet needle valve, which allows fuel to be drawn from the tank, through any filter you might have in the tank, through the inlet fuel tubing, through the fuel pump, through the inlet screen in the carb, past the regulator needle valve, and finally into the fuel chamber. The excess is then expelled through the other line in the primer bulb system, and dumped back into the tank.

So think of what all this accomplishes:

1. Flushes old fuel out of the carb and replaces it with fresh drawn from the tank.
2. Proves that the filter in your fuel tank is flowing.
3. Proves that there is probably no kink nor obstruction in your fuel feed line to the engine.
4. Proves that fuel can flow through the fuel pump, indicating that the check valves in the fuel pump are wet and probably functioning. (At least the inlet flapper valve is not stuck.)
5. Proves that the inlet screen in the carb itself can flow fuel.
6. Proves that the inlet needle is not stuck shut. (I have had this happen.)
7. Proves that the regulator diaphragm is not stuck in the closed position. (It still could be too stiff to operate correctly but at least it is opening the needle valve.)
8. Proves that there probably not an air leak at the fuel pump nor diaphragm cover gaskets.
9. Prevents the "dry carb won't draw fuel" syndrome.

Interesting heh?? I fix a lot of yard equipment, and the first thing I do after checking compression and spark is to put fresh fuel in and pump that primer bulb. If it doesn't pump fuel and fill up, the very first trouble shooting step is to find out why not.

Originally Posted by Antique
Ignition systems 101...My carb rotator block is made from 3/8" epoxy board material...the carb is now closer to the cylinder...The throttle connection is at the end of the carb closest to the crank...The throttle servo connects directly to the new brass arm on the throttle shaft...It makes no difference which timing method is used, the connection remains the same...The mechanical advance has a 4/40 threaded rod link between the carb shaft and advance mechanism, a 6202 ball bearing on the back side of the prop hub...The hall sensor is mounted in a ring pressed on to the ball bearing...There is a magnet in the hub that triggers the advance when it passes the hall sensor...With mechanical advance the ring is rotated by opening the throttle..The spark timing is set for 28 degrees before top dead center for either method...The difference is that full advance is reached at 4000 rpm with electronic advance, and at Wide open throttle with mechanical advance..Contrary to popular opinion, I can find very little difference either way...I don't think the engine can tell the difference where the spark occurs after 4000 rpm, and very little if any before that..
To further complicate this, the electronic advance can be made to delay full advance until 6000 rpm..Again, no difference noticeable in performance..
The difference between my mechanical advance and the Brison pictured is the material on the Brison is Delrin or nylon with no ball bearing, and mine is aluminum with a 6202 sealed ball beaing..My hall sensor is epoxied into the aluminum, the C&H ignition setup on the Brison uses the exact same Sony DN6952 hall sensor in a removeable round piece held in by a setscrew...Since hall sensors rarely go bad I use epoxy...
The sensor on the DA is a small transformer using only 2 wires...The electronic advance on the DA works just like the electronic advance on all other engines...
The electronic advance chip on mine and C&H ignitions is the same part...
Static timing on mine and C&H electronic ignitions is set at 28 or 30 degrees BTDC...The first flip of the prop retards the ignition to 4 degrees BTDC, then follows the rpm of the crank.
Static timing on most other electronic advance ignitions is set at about 4 degrees BTDC and advances to 28 or 30 from there..
Hall sensor electronic ignitions with fire at 1 rpm, the other systems must be flipped a little faster for the transformer sensor to make enough voltage to fire the circuit....
Mechanical advance ignitions MUST be started with just a few clicks of throttle because the engine will kick back if the throttle is opened too far...Other systems always start retarded regardless of throttle position...
Spark timing can be changed on either system, by moving the sensor on the other systems or changing the length of the link on the mechanical...
Older engines with fixed EI can be changed to electronic advance by pluggin in a syncro spark module between the sensor and circuit board and locking the timing ring at 28 degrees BTDC..
Syncro spark modules are available from C&H...
Most engines with magneto and source coil ignition are set by the factory at 28 degrees BTDC....It can be changed by removing the mag rotor or flywheel and leaving the key out, then rotating the flywheel or rotor to whatever point is wanted..The key does nothin to keep the flywheel or rotor from slipping, it's only function it correctly place the rotor or flywheel on the shaft during assembly...The key on a tapered shaft crank is so soft it will shear if the retaining bolt comes loose....
Did I miss anything ?

Last edited by w8ye; 11-03-2014 at 09:37 AM.
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Old 08-29-2012, 01:04 PM
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Default RE: Newbie to Gas General Information

Engine tuning 101, or maybe a source for some troubleshooting ideas?

Some thoughts prior to starting the first time (or starting over again?):

The idle adjusting screw is the one closest to the engine. The high speed furthest away. Turning them in (clockwise) will lean them, out (counter clockwise) will richen.

If you have the factory suggested starting settings, set them there now. If you don't, lets set them both at 1.5 turns from closed. Be gentle when closing these screws completely as they are pretty small and not terrible difficult to damage. This can/will cause adjustments to be erratic from that point on.

Please don't try the first time with the cowl installed. You need to see the fuel line, and easy access to the adjusting scews make things much simpler.

Idle speed screw should have been removed when you hooked up the servo. That's been done, right? You'll be using the radio to adjust your idle speed.

Prop is set so it's at about 1:30 when it comes up on the compression stroke, right? Much easier to flip from here while keeping your balance and your hand out of the prop.

If you've never run the engine, or it's been a long time - a dry carb has a terrible time pulling fuel. The check valves need to be wet with fuel to function properly. Because of that you may want to be prepared to prime the engine through the carb. Another way is to pull the side of the carb held in place by the single screw, and carefully flood the carb with mixed fuel the best you can.

To help the engine draw fuel more easily when the choke is on, closing the small hole in the choke plate has proven very effective. Solder works well, but use what you want. If not solder, consider what might happen to whatever your using if it were to become dislodged and be sucked into the engine. Sealants that remains soft won't cause any damage. Use no more than absolutely necessary to close the hole. The hole is not required in this application.


So, choke closed, low and high screws set per above, start flipping while watching for the fuel being drawn up through the fuel line. If you haven't seen the fuel and nothing has happened after 15-20 flips, the carb is dry! See above about flooding the carb with fuel to wet the check valves, or get your primer out and use that to shoot a squirt of fuel into the carb's opening.

Once you hear the engine start for a second and quit, flip the choke off and it should start again within just a few flips. If it starts and quits again, and you still haven't seen fuel in the fuel line, prime again! You shouldn't have to do this more than a couple of times, and then, only if the carb is dry.

Engine is running:

Once started, let it warm a bit, gradually increasing rpms as it does. After a minute or 2 take it up to full rpm. and hold it there. Adjust the high speed for maximum rpm, then richen until you hear it slow just a bit (maybe 200 rpm if you're using a tach).

Slow the engine down to something near 1/4 throttle and let it cool for a second, then lower to idle speed. Idle speed is when your plane is right on the edge of trying to move on it's own, not much less. Something in the mid to high teens if you're using a tach. Adjust for max idle rpm, if it starts exceeding idle speed, adjust idle speed as necessary to keep it in line. After getting that set, check your transition. Quickly run it back up to wide open to see what happens. If it quits, richen the low speed a little (a little = a screwdriver blade width), and restart. Let it warm for a second, then lower to idle and take it to wide open again. If it quits, repeat the process until you get snappy response (transition) when opening it to wide open.

Once proper throttle response is achieved, go back to wide open and reset that, using the same process as above, leaving it slightly rich again. Try your idle. If that's ok and your throttle response is still good, it's time to go flying. Do that. Further adjustments will be required no matter how carefull you are here on the ground. More is just a waste of time. That's a given. If you're building confidence just messing with it, that's a different story. Knock yourself out, but it's not necessary.

In the air, finally!

There's so many variables at this point, this is just a collection of notes I use frequently. All assume the tuning process above has been done - recently! The engine also has a reasonably fresh and properly gapped plug installed, and the crap trap in the carb is confirmed clean!

A rich engine won't quit!

First flights with carb settings set slightly rich (without being slobbery rich!) are generally safe ones, big confidence builders. Setting up this way intentionally for the first few flights is cheap insurance.

If your engine is quitting, stopping completely, and you are absolutely sure it's not sucking air through the fuel line, it's lean. It's that simple. If it happens when you pull back on the stick, it's probably your low speed adjustment. At wide open (no matter the attitude) it's the high speed. There's also the potential other stuff can be in play, but assuming it's lean to start generally pays off 99% of the time. When dealing with a lean condition, keep in mind that fuel lines sucking air are common. Really be carefull with this one before getting too carried away. A LOT of problems are traced back to fuel lines sucking air. Guys replace carbs prior to realizing this on occasion....

High idle hang?
Your engine is running great, right on the edge of lean, making max power at wide open throttle. Time to bring it in, you pull back on the stick, but the engine does not come all the way back down to idle for several seconds, maybe up to 30 seconds? Here's what's happening. The combustion chamber is hot from being run. Not hot to the point of being hurt, but on the edge (that's where it needs to be to make max power). By pulling the stick back to idle, you've robbed it of a major cooling source - it's fuel, and the air coming in with it. It's going to need a few seconds to cool down when the only cooling it's getting is the air going through it's fins. That's your delay (the high idle hang)! You can hurry this cool down process by throwing some fuel in there, and that can be done with your idle mixture. Going richer with that can hasten that cooling process, possibly to the point of eliminating it all together. Richening the low speed to that extent will very likely require you to raise the idle speed trim, and the resulting idle will be slightly lumpy. Not totally unexpected on a 2 stroke engine, and nothing that's going to cause it to load up and quit. Adjust a little at a time until the hang problem is lowered to acceptable limits, or eliminated altogether.

There's another option here as well. Remember what's causing this to start with, running on the edge of lean on your high speed? Going rich enough on your high speed so the combustion chamber won't get as hot is another solution. Myself, I'll take the lumpy idle solution...

Mid range burble?

There's nothing wrong running it like this, but if it's making you crazy -
I would start by opening the spark plug gap to .024. Sounds nuts I know, but try it. That's been proven to make a noticeable difference. Next is leaning the high speed mixture, a fraction at a time! If the engine starts quitting on you, obviously you've gone too far. Another indication you've gone to far might be you've suddenly picked up a dose of that idle hang (above). That may not be a bad thing, just something else to deal with.

There's another line of thought on the burble as well. That is the burbling is occurring because the engine is so lightly loaded. 3D planes running low pitch props on planes that don't weigh anything are a good example of burble that can be really hard to get rid of. A sport plane might be able to go to the next size bigger prop and make a difference?

Poor low end response?

Moving the stick up from idle doesn't cause a big bog or the engine to quit, but the engine just takes it's time to accelerate. Top end, from 1/2-3/4 throttle on up seems fine? Might be a little rough sounding on this initial acceleration, but maybe not. It's probably rich on the low speed adjustment. Good first place to look anyway.

Hope this helps!

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Old 08-05-2016, 10:48 AM
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Oil Tips -original author "ClippedWings" - submitted by Al Hicks

A few good tips:
* Good oils burn clean, at 15:1, 30:1 or 50:1 and at different mixture settings.
* Cheap oils leave carbon deposits because they don't burn clean, higher oil % and richer settings will result in more deposits.
* Good oils have better lubrication properties, an excellent synthetic oil at 50:1 may have better lub. than another oil at 25:1. Using an excellent oil at 30:1 will increase the engine protection and margin of safety.
* Carb settings can be rich or lean at any given oil %, but higher % of excellent oils at lean carb settings will protect the engine better.
* There is no direct relationship between the power output of an engine and the % of oil in the mix; i.e. having 3% more oil doesn't rob 3% power, sometimes it is the exact opposite, there are too many variables (engine design, clearances, tolerances, metallurgy, operating temp., etc..., etc...).
* There is a direct relationship between the power output and the richness settings of the mixture (assuming all other variables stay the same).
* There are many excellent oils around so using cheap oils should not be an excuse. I am using synthetics such as Mobil1 Racing, Stihl Ultra HP, Penrite 2C Racing, and semi-synthetics such as Husqvarna XP and LS+. All good oils at ratios of 30:1 or more and never had an engine fail due to lubrication.
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