jbloom

This is my first 4 stroke engine, and it's been 20 years since a 2 stroke. I can't seem to get the engine right.

First, the specs. it's a Saito .91 with a 14X6 prop "K" Series Master Airscrew. It's mounted on a Sig Four Star .60. There is always smoke, such that I'd think I could write my name. Anyway, I have a tach and it seems that I can get a max rpm of about 8300. I typically back that off to about 7900 as I've been told I should.

Anyway, the airplane always seem sluggish to come off the runway. I'm sorry, I don't know what the plane weighs, but I had to add 12oz to the nose to get it to balance. So, I'm likely on the heavy side. At any rate, I've tried a click or two to the lean side but the last time, that resulted in a backfire that spun the prop nut off about 1/2 an inch right as I broke ground. So, back to rich, a ton of smoke and average performance.

Another flyer at the field has an ultimate Bipe with a 4 stroke and there are times I think that if he gives it any more throttle, the covering is going to peal off. So, what's up? I have never touched the low end needle. Not sure if that would do anything, though the engine idles at about 2300 rpm it has a tendency to sputter and die if I let it idle too long, say about 30 - 45 seconds. Which means I tend to land a bit hot, not shutting the throttle down until I'm almost on the ground.

So how about it, can someone give me a no non-sence approach to adjusting the 4 stroke so I can get peak performance. The manual says I should see a max rpm of 11,000. Perhaps a 13X6 or 13X8 prop would get that. But I think the 14 isn't gonna get me there. Thanks!

John

Hobbsy

My Feedback: (102)

Your low speed needle is rich, just peak the top and leave it peaked temporarily, lean the lowspeed needle 1/8 turn at a time checking the highspeed at full throttle with every other change. One of the 1/8 turn changes will make a greater difference than than the previous ones. You'll know that you're getting close. Set idle about 2,000 richen top 200 rpm and see how the transition to full throttle is. If hesitent or it quits its a little lean, you may have to sacrifice a little idle smoothness to get the best transition.

TimC

jbloom, my 4*60 is set up just like yours (Saito .91/14x6MAS). Rather than add weight, I fabbed some extensions out of steel flat bar to move the engine out until it balanced. After break-in, I ended up turning the idle screw in almost 2 turns from flush before the transition was quick and clean. My 4* will take off at 1/2 throttle. At full throttle it will roar and pull the plane airborne in about 50'.
Edited to add: jbloom, I'm running a Cline regulator so the 2 turns in from flush might be way different than what yours will require.

jagnweiner

My Feedback: (1)

JBloom-

Listen to hobbsy, as he knows what he is talking about. My only input is that I have a Saito .91 that I have run with an APC 14X6 and a Zinger wood 14X6 and with both it peaks at around 9600 rpm. I then richen it up to peak at about 9200. You're quite a ways off.

The 14X6 is a fine prop for it. You may not reach 11,000 rpm, but I'm not sure you really want to. There should be no need to switch to a 13 inch prop. That would be too small, in my uneducated opinion.

-Scott

jbloom

thanks Hobbsy, TimC and Scott... I'll give the idle screw a tweak and see what I get. I've heard that once on 4 strokes you'll never go back. I'm hoping for that epiphany!

John

jagnweiner

My Feedback: (1)

You'll get there. This is my first 4 stroke and I love it. I actually still need to fine tune my low end needle. My idle is still up around 2900. I just haven't gotten around to taking the cowl off to do it.

-Scott

islandjack

I have .71 OS four stroke that is turning an 12x8 2 blade peopeller or an 11 x8 three blade for scale looks.. If I can get it started, which is rarely, It will idle low and stall when I take the glow plug off. Then when I try to start it, again, the compressions so high the started motor will hardly turn it or It will fire one time and fuel mist comes out of the carb. It is mounted inverted. I have tried adjusting both the low end screw and the high end needle in and out as far as they will go in all thier permutations with no success. I have an OS.50 two stroke I never have any problems with. I'm thinking of putting a 2 stroke in the plane and say screw the cowl and looks just so I can fly once and a while. Can any one help? PS All of this equipment was given to me by a friend who is out of the hobby so I don't really know much about it. I'm going to put the motor on a test stand right side up and go through all the adjustments again, then I will truly be at my wits' end.

rcdude7

My Feedback: (264)

I'm really puzzled about the GC problem you guys are having? I have built 4 of the fourstar 60 KITS and never had to add ballast with a FS .91 engine in front. Are these ARFs you are flying here?

BTW, don't be afraid to adjust the low needle, it is similar to a two stroke in how it causes the engine to behave. It is the HI speed needle adjustment that deviates from the typical two stroke.

A lean four cycle will always come to a complete stop as it tries to kick off the prop, spinner and nut!

TimC

Yes, the ARF's are tail heavy. Those that have built from kits report no problems.

tamro

I have a .70 4 Stroke OS and just started working on it to put on a profile i got. what should i set the Needle valve to reach the 9600RPM? i started with 2.5 and ran it on the table for about 8 tanks then leaned it out and ended up at 1 full turn and 11 clicks to give me what i can tell a good RPM?

Thanks

w8ye

My Feedback: (16)

That sounds about right from my experience with Magnums.

The needle valve is adjustable so you can tune the engine properly.


If you like the power it makes, then everything is OK?

airmodeler

Can you help me with my engine problem? I have an ASP 91 four stroke engine that quits after I remove the glow starter from the plug after I have the engine started.

jaka

Hi!
Glow plug: OS F plug.
Propeller: 14x6 APC, RAM or Graupner G-Sonic prop.
Fuel: 5-15% nitro and 20% oil (Castor or a mix of Castor and synthetic).
Have you adjusted the needles? You have two! One i the high speed needle and the smaller one is the low speed needle.

airmodeler

Thank-you for your reply. I researched engine tuning and I found a procedure that really helped.

Hobbsy

My Feedback: (102)

Air, one good plan is to set high speed needle at full peak and leave it peaked temporarily, sometimes at full peak the rpm will wander up and down a little, go one click rich and it will be very smooth. Now set the LS needle by leaning it 1/8th turn at a time and you hit a sweet spot. Test the transition after every other needle change.The LS needle controls the mixture for about 85% off the throttle range so it has a huge effect on economy or the lack of it.

Slow-Flyer

Hi all,

I know this is an old thread but people are still reading them.
I remember reading this a while back so I decided to come back and add my 2 cents worth. :-)

Hobbsy has very good advise in my opinion!
However, I would like to add a little to it.
I had one of my 4 stroke engines running really good while the plane was level on the table so I was happy. (This was when I first started learning about glow engines)
The rpms would increase slightly when I raised the nose to vertical which was good but when I cycled the throttle from idle to full speed, the engine wanted to die unless I lowered the throttle back to idle again. This was due to a lean idle mixture setting so I had to richen it about an 1/8th of a turn at a time until the transition was good (while pointing the nose up). I didn't have to readjust the high speed needle more than 1 or 2 clicks after readjusting the idle mixture as it was already pretty close while the nose was raised.
If the engine rpms increase quite a bit when the nose is raised, it's likely that the mixture is already fairly lean, if the rpms lower when the nose is raised, it is for sure quite a bit too lean. If the rpms do not change at all, it's likely that the mixture is just too rich. With a proper setting, the rpms will increase slightly and that is what you want in my opinion.
Having your engine set right for vertical means you will have a slightly richer idle and a slightly richer high speed setting than you want when it's level. The rich idle is usually not as smooth as full throttle but it is a trade-off and it is obviously mandatory to have a good running engine while vertical.
Also, the engine should run about 10°F cooler (average of about 190°F on most of mine, I use a beaded K type thermocouple temp probe rather than a IR temp gun to check the head temps).
Fuel economy is a little less but not much, with my OS 70S II for example, I am getting about 1.5 minutes of run time per ounce of fuel (I usually use 15% nitro on 4 stroke engines, I use 15% because it only fires on every other up stroke so it needs a little extra nitro to keep it running reliably, with 2 strokes, it's fine with even 5% nitro since it fires on every up stroke, this of course is simply my personal preference for peace of mind.
Also, I have found that a tightly cowled engine causes the engine to run hotter than it should and that extra heat has an effect on tuning as well, so I always open the cowl up as much as possible even it doesn't look as good as I'd like.

Another observation that seems to have an effect on tuning is the glow pug and the glow plug driver (glow plug battery).
Most people are fully aware of the importance of having a good glow plug but they may be ignoring the importance of a good glow driver.
I had an engine once that was tuned good and I would sometimes have to tweak the high speed needle slightly but that depends on weather conditions, overall, it ran good everytime I flew.
One day while at the field, I started the engine but it was like the needles were out of sync again. I figured that the glow plug must be worn out but installing a new glow plug didn't help at all!
Even with the battery still on the plug, it would not run good, it was like it was way too rich even at high speed and with the new glow plug.
I decided to attach the glow driver to the glow plug that I just removed and the glow plug was barely red, it was very weak but when I did the same on a new plug it was the same as it was with the old plug.
I just happened to have a fresh glow driver with me so I tried that one on the removed glow plug and the glow plug lit nice and bright.
Then I decided to start the engine with the weak driver, then just touch the fully charged glow driver to the new glow plug and when I did, the engine was back to normal again.
I recall running a horizontally opposed twin cylinder engine where I could start the engine on one cylinder, then just touch the glow driver to the other cylinder and that would get both cylinders firing as they should.
I had always thought that after the engine is running (even with a weak glow battery) that the glow plug would get hotter after it starts, especially with 15% nitro but that doesn't seem to be the case.
If you find yourself not being able to tune your engine, it could be that the glow driver is weak. I recommend to always start your engine with a good glow driver and a good glow plug.
I read somewhere that a glow engine could be started without a driver at all if the engine is turned over fast enough but I'm having trouble believing that claim now (unless maybe they're using 50% nitro, Lol). The fact that a twin cylinder engine still has to have the non energized cylinder touched with a glow driver is further proof that the above statement of not needing a glow driver just isn't true.

I hope this helps someone who may be having trouble tuning their engine.

Again, great advise, Hobbsy! :-)

Jesse Open

the Wasp

My Feedback: (1)

that must have been quite a surprise to you, I will try to remember not to do that !!

Jim

the Wasp

My Feedback: (1)

to me that sounds like those plugs were to cold for the fuel you were burning (in that engine), but maybe the fuel had started to go bad or become contaminated, after all many and most of us flyers at the end of the day do empty our fuel tanks back into the clean fuel in the gallon jug after the exhaust has contaminated the fuel to some degree,, but too it could have been a freak thing, cause in this hobby just about anything can happen

Jim

Slow-Flyer

That was just my personal observation and personal conclusion.
Keep in mind that is wasn't a huge difference in rpms but I could tell that it ran slower than normal as though it was running too rich, it seemed to really struggle at idle.
I always use OS "F" plugs made for 4 stroke engines, I can only assume that they are hot enough since they kept the engine running during break-in at 5 turns open on the high speed needle without a glow driver. I usually break my engines in at full throttle but rich enough to max out at roughly 4000 rpms by using a super rich mixture. Seems that a plug that's too cold wouldn't run an engine that rich without a glow driver attached.

I always fill the tank with fuel after a run to force the exhaust gases out of tank, then I leave the fuel in the tank even during storage, I only use aluminum and stainless steel hardware in the tank so there's no chance for corrosion, brass always has that green crud on the surface in a short time because of the exhaust gases.. I always use a clamp on the pressure line from the muffler as well as a clamp on the line to the carb to prevent leakage and to prevent air from getting to the fuel and plumbing in the tank. I never pump fuel from the tank back into the jug, mainly to prevent contamination.
I also seal the gallon size glow fuel jug to prevent evaporation, Fuel will evaporate pretty quick when the container is left open to air.
I wanted some of the synthetic oil once and the only way to get it without ordering some was to pour a few ounces of fuel into an open plastic cup, then just allow the nitro and methanol evaporate, it only took a few days for that to happen.
The fuel I used is fresh, a gallon rarely lasts me more than 3 weeks, most of the time just a weekend but it depends on weather and my mood. I never use left over fuel from the previous season just to be on the safe side. I usually keep a little leftover fuel for cleaning engine parts during the winter, otherwise, I try to not have any leftover fuel laying around that won't get used.

Maybe it's a 4 stroke thing? I've noticed that my 2 stroke heli engines run 50 to 75°F hotter that my 4 stroke engines so that makes me wonder if the "F" plugs are hotter than an OS #8 plug made for 2 stroke engines. I'm no engineer or any form of any expert so I don't really know, again, these are simply my personal observations.

As you say, anything can happen in this hobby :-)

Thank you for your feedback!! :-)

Have a great day!!

Slow-Flyer

Wow! You held onto a running engine with a prop on it? You are a LOT braver than I am!
I would have tossed the thing immediately, it would have been an automatic reaction to toss it immediately just to preserve my body parts. :-D

How much WD40 did you use? I would think that it wouldn't have turned over more than a few times on just a shot of WD40 but I wasn't there to see it.

Check out this video where a guy runs a 2 stroke glow engine on WD40, he runs it at 50% nitro & 50% WD40 and it seems to runs fairly good. Then he runs it with 25% nitro & 75% WD40 but the performance was not good, then he "Tries" to run it on pure WD40 but it won't start even with a glow driver attached to the glow plug.
Could you post a comment on his video and explain to him how you were able to start a 2 stroke on WD40 without a glow driver? I'm sure he will be very interested in how you did it.
You'll have to copy and paste the title of the video into the the video search bar on YouTube since I'm not allowed to post URLs until I have enough posts (I'm new here).
Here's the title to the YouTube Video:

Nitro Engine Running on WD-40

Here is a video of a twin cylinder glow engine that was started on one cylinder (just one glow driver), then the glow driver has to be attached to the other cylinder to get that cylinder to fire.
I would think that if the heat of the cylinder alone could light the glow plug that a twin running on one cylinder at roughly 1000 rpms it would light but no, as you can see, he has to attach the glow driver to the second plug to get it to light.
Watch the video from 2:50 to 3:05 to see the engine increase rpms dramatically after he touches the glow plug to the second cylinder with his glow driver.
BTW, the guy had a remote glow driver connection for both glow plugs to light at once but the glow driver didn't have enough juice in it to light 2 plugs simultaneously so he had to light them one at a time.

Again, you'll have to copy and paste the title of the video in the YouTube search bar.
Here's the title to the YouTube Video:

1/4 Piper Cub FT-160 Twin Cylinder Ringed Engine

Could you start that Super Tiger on WD40 again with video so we can see it? That would be great cause I really want to see that! :-)

You are a brave soul, for sure!! :-)

Thanks for your feedback!

Have a great day! :-)

Jesse Open

Slow-Flyer

I totally agree that different people react different, as you say, some react while others respond, that's why I stated that you are braver than I am. I would think that if the engine had been tossed toward the floor it would have hit a solid object (the floor) and quit running before it had a chance to buzz around aimlessly like an inflated balloon released without a knot at the opening.
I was running a flap disc on a side grinder when it accidentally picked up a small wire that turned it into an extremely dangerous weed wacker, I immediately threw it to the floor and unplugged it as it was spinning around on the floor aimlessly, I can only imagine what it could have done to my hand if I had held onto it while trying to turn it off.
There was a gyroscopic element to that disk rotating at 10,000 rpms and that could have caused additional issues but that wire was extremely close to my fingers since the disc was at a 90° angle from from the motor and the motor "IS" the handle.
I'm sure there was a gyroscopic element to the running glow engine as well (how much would depend on how fast it was running).

I don't know when this happened but WD40 stopped using propane at some point and replaced that propellant with carbon dioxide (CO2) but even with propane I fail to understand how it ignited without the presence of some type of spark since the autoignition temperature of propane is nearly 900°F (not the flash point and in the form of gas rather than liquid). If the autoignition temperature was that low, it wouldn't be safe to use in home heating systems or combustion engines. I'm having a hard time understanding how the compression could be high enough to produce that kind of heat with a single flip of the prop.
I have a utility cart that runs on propane, there was one instance where I couldn't get it to started because the ignition system quit working, the gas regulator and delivery system was working properly, it just didn't have any spark.

Freak things can happen and those instances rarely have a scientific explanation.
I'm not saying that it did not happen but I would have to conclude that your experience is at the very least extremely rare and should be considered extraordinary (if not a one time thing that could be an historic event).
The statement in my original post was referring to the ordinary rather than the extraordinary.

BTW, I wasn't suggesting to try starting it again while holding it in your hand, I would try it again with the engine on the plane or on a test stand for safety purposes.

Anyway, thanks again and have a great day! :-)

the Wasp

My Feedback: (1)

my son (16) was flying a friends plane, it was his 2nd year of flying, he was up maybe 20ft at the most, upside down at the top of a loop, so yes the engine stalled, as the plane was coming nose/straight down I had a quick thought that I would be shelling out some money, well at that moment of thought he pulls back the stick, the plane levels, the wheel touch the ground without a bump and the plane rolls to a stop, one guy was right behind us watch, he just turns and walks away, what could he say,,,, me ? I was jumping up and down swinging my arms yelling "yes yes that my son, that's my boy, that my son, he did that he did that, what a landing",,, I feel if he pulled back 1 second later the plane would have been damaged in some way, that landing was 1 in 100 Million

Jim

the Wasp

My Feedback: (1)

well in that case of that engine starting on WD40 without power to the Plug it's easy to understand, that engine Dieseled on him, he flipped it over just the right amount of times for the WD40 to heat up and spark

Jim