I,m getting good rpms at full throttle, somewhat rough idle.......when I bring it back from full throttle it wants to cut out. Any suggestions, thanks

Hard to say from that small bit of info, but it may be lean. Is the result the same whether you quicky go from mid to full and down vs. leaving it at full for a longer period of time? Is the engine new, partially broken-in or well used? What happens going from idle to full throttle? Does it hesitate and then catch up or frequently just stop?

its pretty well broken in. It was stalling when opening full throttle. I went a little more rich, now it runs good wide open, pretty rough idle if it stays running from full. I think transition is ok from idle to full

Also it depends on which carb you have

A high speed nozzle/check valve assembly helps prevent the stalling when you chop the throttle

In theory, the low speed should be as lean as possible and the engine still be able to accelerate to full speed from idle without sagging

thank you

The two needles will inter-react with each other to a certain extent. You adjust one and you have to go back and check the other.

You have to continually check full throttle (in the maneuvers also) and then cut the throttle and listen to the idle.

Some people program in a higher in flight idle and at flare out when landing they flip the switch for the touch down idle.

I,ve also noticed that when at full throttle it sometimes takes several seconds for the engine to idle when I bring it down fast. I checked that the servo pushes the throttle arm all the way closed & it does. Can it be just burning off the extra fuel before it goes to idle?

Your low needle is to rich.

I always thought it was cooling down during those several seconds. Running a little rich on the low speed will help minimize?

In my experience a two stroke engine that is slow to come down to idle speed after being at high throttle is often set too lean.

Man, an engine will tell you what it wants if you know how to interpret the sounds, but that is nearly impossible to describe to someone....

AV8TOR

A slightly rich engine will fall down , and then recover rpm. Slightly lean will be slow to fall down in rpm. Slightly rich is best for stable running and good starting. Too lean will cause flame-outs and unreliable engine rpm while landing.

AV8TOR & Pe Reivers...if you are like me...the sound of a out of tune engine bugs me to ne end! Capt,n

Yep!! Years ago I had a girlfriend with a hot rod car I built for her. Sometimes when someone checked the oil and didn't pay attention, they could accidentally knock one of the spark plug wires off. My girl had an early morning paper route, and I could lay in bed and hear her going from house to house when in the area where I lived. I could hear that car missing and it would drive me nuts!! More than once I flagged her down in a robe when she passed my house so I could put the spark plug wire back on!! I would always say "CAN'T YOU HEAR IT MISSING????" Yeah, an out of tune or missing engine makes me crazy.

AV8TOR

An engine that misses where it should'nt bugs me too.
However, two strokes do tend to miss near idle, especially if underpropped and there is no engine load at low rpm. This is the sound I learned to like, because it assures proper idling forever and a day.

Well yeah, that's like a four stroke engine with a hot cam; a unique sound, not a miss. A two stroke at idle has a unique sound too, and I can spot one a "mile away" that's rich or lean just by the sound. But I have found that recognizing the various sounds of an engine is a hard thing to teach to people, much less explain the sound in a forum.

Anyway, a two stroke that is slow to come down to idle and has kind of a buzzing sound instead of a mellow "pop, pop, pop, poppity pop" sound at idle is usually too lean.

AV8TOR

Talking about engine sounds, I was just about fooled on the sound of a Big SuperTiger 3000. I thought it was a normal gas engine sound with CDI ignition. Afer the guy landed his warbird, when asked he told me the engine was running on E85 with a hot "F" style glow plug. I am not trying to convert anyone to do the same...but I may try it. It sounded very good! Capt,n

Hi,

Typically when you have to back out the needle valve a lot to keep the engiine running, it is due to the "O" rings on the needle valve leaking air. They leak air into the fuel and you have to open the needle valve to compensate for the excessive air. The fix is to replace the "O" rings, but they are usually very hard to find locally.

In a pinch, I've been able slice a cross section of fuel tubing very thin and fit it into the "O" ring grove. Unfortunately, fuel tubing comes in different sizes and with different thicknesses of wall. I keep the old small pieces of old fuel tubing from ARF fuel tanks, fuel lines etc. and usually I can find one with the thickness I need.

However, the best thing to do is get the proper "O" ring. Perhaps someone here knows of a good local source.

Hope this helps.

Fly4Fun,

Wayne

Wayne,

We are talking about gas engines here not glow.

Karol

Some small gas engine carbs do have a sealing ring of sorts at the base of the needle. The spring around needle places a tension on a flat washer and between that washer and carb is a special shaped sealing ring. I know....they are darn easy to loose when you take the needle all the way out. You will never notice it unless you check close for them in the first place. Capt,n

Hi,

Sorry, I failed to notice you were talking about gas.

Fly4Fun,

Wayne

I'm having a similar issue to this here. I'm running a 3W-80xi with a 26x10 prop. We've been having issues with the engine running rough and cutting out at idle lately and have been trying to retune the carb.

We start by tuning the high end 100-200 rpm lean of max achievable rpm - this works fine. When we go to tune the low end the throttle adjustment screw requires a lot of screw in to even hold an idle. We've then been leaning the low needle which causes the engine to rev up allowiing the throttle adjustment screw outwards. When we go about this process the engine revs up without any hesitation however, it doesn't want to come back down the idle rpm, it hovers around 600-700 rpm higher than idle and will only come down when the throttle is "pulled" closed further. We've also seen it sometimes hunt around to find an idle, varying +/-400 rpm around a little above idle.

From the posts above, it sounds like we're leaning the low needle way too much and should even consider running slightly rich to avoid the engine quitting in the air.

Does anyone have any more in-depth methods for carb tuning or any suggestions to on how to proceed? Also, does anyone with experience with this engine have recommended rpm settings for full throttle and idle? We're currently shooting for around 1800 rpm at idle at 5800 at full power.

Thanks in advance.

-Rick

Is there any chance you can apply the choke for just an instant? If you can, and the idle comes down and stays there once you release the choke, you're experiencing the lean problem above. Maybe others will understand what you're saying better, but you're loosing me when talking about "pulling it down". Are you talking about applying an "idle kill" throttle position? Are you experiencing a linkage issue maybe?

I'll give the choke a try and see where it gets me.

When I refered to "pulling" the throttle what I mean was this. I set the throttle adjustment screw so that it would hold an idle when the throttle is fully closed (Ican kill the engine with an electronic kill switch). The engine *seems* to return to the normal idle speed when I "pull" the throttle further closed (it doesn't really move much since it's up against the screw).

It's not a linkage issue, the engine is currently on a test stand and there is no servo or linkage hooked up to the throttle, we're adjusting it by hand.

Thanks for the reply.

-Rick

If you let it, will it continue doing the high idle thing indefinitely, unless pulled down? Or will it eventually come down on it's own?

I believe that eventually it will come back down after ~1 min or so, I know we tested this but can't remember the exact timing. That's what was making it sound like it was slightly lean, as the posters described above.

Thanks,

-Rick