I was having a problem with my Ryobi missing a little at WOT.  No adjusting on the needles would change anything.  I thought it was running rich.  Was running an RCexl ignition set at 28 degrees.  For last attempt, I advanced the timing a little bit.  Made it worse. Retarded the timing a little bit pas where it was originally.  Whole different engine.  Ran so sweet I could have sworn it was a differernt engine.  Have had a couple days flying time with it and no change still runs perfect.  I have it spinning a MAS 18x10 classic prop and flying a rather heavy , been repaired several times, Sig 4 star 120.  Thing weighs almost 15 pounds dry but the Ryobi with this set up pulls it great.  Will do an outside loop from level flight at 3/4 throttle. 

I had about given up on this engine until I made that slight little change.  So dont forget about adjusting timing a little also.  It may take a little trial and error until you hit the sweet spot.

Jim</p>

Jim how did you set up your timming when you set it at the inital 28 degree?

I did it while the back was still off the engine.  I had decided that I wanted the sensor to be located on the bottom of the engine.  I then placed the crank at TDC and rotated the crank 28 degrees using a degree wheel.  I then marked my hub for the magnet where it matched up to where I wanted to mount the sensor.  The engine is mounted inverted on my airplane so it is real easy to see the sensor and make adjustments.  To get to the sweet spot, I moved the sensor a couple of degrees counterclockwise as seen from the front of the engine. 


Jim

when you say retarded it it is set at 60 degrees or past 30 degrees I tried to adjust it while it was running and it just quit michael

I am not sure I understand your question.

Jim

Jim from what your describing you used your timming wheel to figure out where you located your sensor and magnet. It sounds to me like no procedure was used to find true tdc and you dont know if your degree wheel was set at true tdc. not really necassary to just located where you want your mag and sensor as a few degrees here or there wont matter, but very necassary to get your spark set correctly at the desired degree of 28 deg btdc. then it sounds like you installed the magnet and the sensor and no procedure was used to verify what the spark timming actually was. the engine was then run and the timming was adjusted by hand and ear to what you consider to be the sweet spot. so in all actuallity you have no idea what you timming is actually set to right?

Im not trying to beat you up on this im just trying to understand your method.

well I used a wooden dowel and rotated the piston to tdc and set my degree wheel to 0 and from what i have read there will be a little play in the crank so i moved the crank untill the piston moved and moved it back to 0 and moved the crank the other way till the piston moved there was about a 2 degree movement in both directions so i devided it by 1 and reset my degree wheel to 0 and went 28 degrees btdc did i do it about right michael

With the back off the engine, I could see the crankshaft.  I mounted my degree wheel on the crank shaft.  I moved the crankshaft by eye to TDC by looking at it through the back of the engine.  I then moved the crankshaft 28 degrees BTC and marked the hub at the spot where I wanted the magnet to be.  I could have put the magnet and sensor anywhere on the case but I wanted it set at the very bottom of the engine.  The hub was marked where it matches up to where I wanted the sensor to go with the crankshaft rotated the 28 dgrees BTC.  Once again, I located tdc by looking at the crankshaft with the back plate off and the crank pin at the top of its travel.  You are right in that it is not the most accurate method and a small amount of movement can be several degrees.  That is why I learned that with this method it is necessary to fine tune afterwards when ready to start running the engine.  There is also a variance of when the spark occurs when the magnet passes by the sensor as well that has to be adjusted for.  I dont think it is possible to get it exact just from measuring because of the variances.

Jim

Dont worry about beating me up.  If you have a better idea I would like to hear it.  I am just a novice at this and am learning as I go along. </p>

Ok Jim. I am not worried about beating you up as much as you taking it that way lol. Learning is why were all here.

Ok so here is the method to get it dead nut right on.

When you rotate the piston to tdc there could be as much as a6 degree dead spot where you can rotate the crank and there will be no piston movement. the idea is to set your degree wheel right in the middle of this to where you have equal amount of dead spot before and after 0 deg on your degree wheel. so you can see by eyballing it you can be as much as 6 deg off right off the bat. there is two methods that can be used to acomplish this. first uses a dial indiacator and the second uses port timming to set the wheel.

first method. you must mount a dial indicator to where you can measure piston travel. i used an old spark plug and made an adapter that goes in the plug hole and then clamps the dial indicator in place. the degree wheel is also installed in this process.






ok so with the dial indicator and the degree wheel installed you rotate the crank till the piston stops moving. set dial indicator to 0 and move deree wheel to zero. rotate the wheel back and then slowly rotate it till the dial indicator just stops. note this number on the degree wheel. keep rotating it till it just starts moving and note this number. the difference is the number of degrees the piston trave is dead. move the degree wheel to where 0 is in the center of this dead spot. ie if you have a 4 degree dead spot there should be 2 deg bfore 0 on the degree wheel and 2 degree after 0 on the wheel. It is absolutly imposible to acuratlysee when the piston stops and starts moving without a dial indicator.

Ok second method. If the piston has a dead spot at tdc then it stands to reason that there is a dead spot at bottom dead center. true tdc can be found by finding true bdc using the port timming. how do we find port timming? install degree wheel and remove muffler. rotate crank through and looking into the exhaust port slowwly rotate and stop when the piston just opens the exhaust port. note this number. keep rotating through and stop when the piston just closes the exhaust port. the difference between the two numbers is the exhaust timming. ie if the exhaust opens at 250 degrees and closes at 110 then the port timming is 140 degrees.

There should be an exact number of degrees from port opening to bottom dead center as there will be BDC to port closing. meaning if port timming is 140 degrees there will be 70 degrees from port opening to bdc and 70 degrees from BDC to port closing.

Ok so we know the port timming and we know how many degrees there should be from port opening to bdc. so rotate the crank till you reach where the port just opens again. set your degree wheel to where it is half the port timming before BDC. rotate through till the port just closes. it should be the exact number of degrees after bdc that you set the degree wheel for when the port opened. if not keep adjusting till you have equal amount of degree before and after BDC from port opening to port closing. now you have true bdc set and it will also be set for true TDC as it is exactly 180 opposite.

Make sense?

ok now we need to set the spark timming. This is the procedure that i was told to use by ralph at ch ignitions and it does work.Dont worry about any of the computerized advancing or retarding of the spark with this procedure as the ignition will know what you aredoing and it will not advance or retard while you are doing this. Ralph saysthe box is smarter than any three areomodelers put together and i think he isso right on this.with degree wheel set at true tdc and all ignition parts installed and battery installed and ignition turned on slowly rotate the crank till the ignition sparks. not this number. this is where the sark timming is set. ie if it sparks a 16 deg before TDC then yo have 16 degrees of advanced timming. do this a few times to make sure you have the right spot. adjust your sensor so that when you rotate the crank through very slowly it will spark at 28 degree before TDC. you will now be set dead nuts at 28 deg BTDC.

This is how i set mine and it runs dead nut perfect. if i move any direction from this setting there is absolutly no power gain and only worsens performance.

I hope now you can see that when you say you set it to 28 degrees as you did in this post

is very misleading information. you actually have no idea that you were actuallyat 28 degree. i really think what happened is that you were way off of 28 degrees and by hand and ear tunning you manged to find a spot on or near 28 degrees to where the engine ran satisfactorily. again you have absolutly no idea what your engine is set at.

Again not trying to beat you up on this but just trying to help you understand what you have.

Using the "positive stop" method.  You screw a tool into the spark plug hole to stop the piston from reaching top dead center.  This is the way we do it on race car engines:  This is a quote from a post I made some time ago:

(QUOTE)   Eyeball the piston at TDC. You can use a rod or something and feel for it, or use a dial indicator. Then set your degree wheel so that the pointer is pointing at Top Dead Center.

Then install your piston stop. Rotate the crankshaft so the piston touches the stop and note the degree reading.

Rotate the crank in the other direction until it touches the stop and note the reading.

If the readings are exactly the same, you lucked out and set the degree wheel properly by chance.

More likely, the readings will be different by a few degrees. Let's say one reading was 44 degrees before top dead center, and the other was 50 degrees after top dead center. Move your pointer or degree wheel to half that distance. (In other words split the difference and move the wheel or pointer 3 degrees.)

Now rotate the crank in both directions and note the readings again. They should be equal, or very close. If they are off a bit, adjust the wheel or pointer again. You want the reading to be the same each time the piston touches the stop.

When you have achieved this, you can remove your piston stop, and now when the pointer/degree wheel indicates zero, or TDC, the engine will be at it's true Top Dead Center.

You can then set your ignition timing, check your port timing, etc.

The site <font color="#00265e">www.ch-ignitions.com</font> has a printable degree wheel you might find helpful.

To prove to yourself that a dial indicator doesn't show true top dead center, try this. With your degree wheel and pointer in place, install the dial indicator to indicate off the top of the piston. Now very slowly turn the engine over until the dial indicator stops rising. Find the exact point where the indicator stops rising, and then stop turning the engine over and note the degree wheel reading. Now once again, slowly turn the engine over in the same direction until the dial indicator starts back down. You will notice that you can turn the crank several degrees before the dial indicator starts back down. This is called piston dwell, or the time the piston spends literally stopped at TDC while the crank "flops over" and starts pulling the piston back down. This amount varies from engine to engine, and is related to the rod/stroke ratio and other factors, but it is why a dial indicator can't ever show you true TDC unless it is used to measure a certain distance down on either side of TDC, just like the simple and preferred "Positive Stop" method.  (END QUOTE)

The other thing to know, as mentioned, is that you need to use the degree wheel with the ignition system all hooked up.  When you actually see a spark at the plug at 28 degrees on the degree wheel, you're set.  You can't just position the magnet/sensor setup, you have to actually see the spark because the spark doesn't actually occur until the magnet is <u>leaving</u> the sensor.

AV8TOR <span class="info"></span>

Man I have never heard of that method but yea that would work great. See it just goes to show no matter how long you been doing anything there is ALWAYS something new to learn.

its nice to knowyou have your engine set up dead nuts. sure takes all the wondering and guess work out of it.

I had never thought of resetting the timing with the ignition on before.  Seems so simple now.  Next chance I get I will recheck it again just to see where I came out.

Jim

thats pretty much how i did mine

Here is a link to a post that shows the "piston stop" tool that I made to use on these little engines.  Its pretty handy...

http://www.rcuniverse.com/forum/m_23...tm.htm#2346520

AV8TOR

I went back and reset the timing using the method you guys described.  I had it set around 15 degrees BTC when I started.  When I set it at 28 degrees BTC, it was right where I had started.  And at WOT it randomly missfire.  I moved it back to about 20 degrees and it smoothed out and ran normally.  Any explanations?

Jim

sounds to me like your using your timming to compensate for what tuning your lacking in your carberation. If you are accurattly set at 28 deg and it misfires or what has been reffered to as four stroking ( cause it sounds like a four stroke motor) then it has to be that your carb is not set right or you have a carb problem.

Also I went to spad fest saturday. man what a cool event. Everyone said I had the best running ryobi they have ever seen. Looking at some of the other planes i really want to do a quad spad with ryobi engines. I think i got next winters project lol.

I could never get it to tune properly with the timing set at 28 degrees.  But with it set where I have it now, it tunes properly and runs great.  Has real good vertical with my almost 15 lb 4 star 120.  It will climb out on take off at around 60 degree angle with a MAS 18x10 prop.  Starts easy and idles well.  I think I like it just where it is.  But I have no explanation for it.   Maybe it is the ignition.  It is an RcExl ignition.  I had an XYZ ignition on it at one time and if I remember right, it ran at the 28 degree mark.

BTW, the carb has a new overhaul kit in it. With new screens, fuel pump and gaskets, regulator, and needle. 


Jim</p>

Well i guess well just have to chaulk it up as a case of pure magic LOL.Words removed by moderator

There is no cut in stone rule the timing has got to be spot on 28 degrees. That is a good starting point for a lot of engines. Do you know that a lot of old time model airplane ignition engines had a lever to set timing which is advancing or retarding the timing. Get your engine huming (top rpm) and set timing where top (peak)rpm is achieved and if needed adjust carb for good low end idle. Also do not be dumb and run wide open very long. Drop the top RPM by setting the carb richer. Say maybe drop it about 100 RPM. If your engine runs good...do not be concerned about the 28 degrees. Capt,n

Don't forget that the  ignition fires when the magnet passes and is leaving the sensor, not center to center

I know that the timming is 28 degrees to start with and adjust from there. when I set my timming at 28 degrees it would miss atwide open so I started toadjust the timming a little at A timetill it quit missing. and I adjustedthe needles so far with anew carb I get 7000 rpm. It will not hand start so I use my starter safer on the hand will see hoe it dose in the air michael

Ralph woudnt you agree that if the ignition is correctly set to 28. and i do mean correctly. then if it is misfiring at wide open and it cant be tuned out with the needle vavle then maybee the diapram settin isnt right. Would you agree that changing the timming at this point is just adjusting around a improperly working carburetor? Am i just way off on this????

its a new carb or that degree wheel was off michael

I do understand that it is a new carb. I dont think that necassarily garuntees that the diapram is set right. also i got no way of knowing that your actually set to 28 deg. al i can do is take your word for it. I dont know if the best timming is variable per engine so i was asking someone that has set up way more of them than I as i have only set up one and it ran spot on at 28 degree. I am very certian i have or should say had before it crapped out, mine set precicely at 28 degrees.

If the timing is to far advanced, like 35 + deg BTDC then it may develop a HS speed miss, almost like it is to rich. BUT you can't tune it out using the carb needles.