I’m usually pretty good adjusting my engines; but I’m having a problem with a new gasoline engine that has me stymied. Now this engine is new and only has about a gallon of fuel through it. It’s a small, 25cc Roto with a Walbro carb.

The engine runs well enough both in the air and on the ground except for the two problems related below. I am currently running the engine on a 32:1 mix, sea level, moderate, to cool temperatures.

I have tried adjusting both the low and high needles substantially. Going substantially rich or lean does not seem to help. I’m just wondering if I have to run this engine more before it will start to settle down. I do let the engine warm up before I set idle or fly it.

Problem #1: The plane lands, at the end of a flight, with a much higher idle than it started with (guess that’s better than a lower idle [] ).

Problem #2: If I move the throttle quickly from idle to open the engine will hesitate or die unless I catch it by reducing the throttle. It does not do this going from wide open to idle quickly.

I'll vote for not broken in yet. If you have the manufacturer's recommended needle adjustments, go back to them and start over.

Dr.1

You are lean on the high end...

Hewre is how I do all my engines as instructed by RCIGN1

Open both 2 turns
Start engine
Lean out high speed needle for max rpm, then back off about 200 rpm
Slowly lean low needle and try transition
Do it until no transition
Open low slightly until transition is good
Re set high, leave slightly rich


If the ‘H’ needle is too lean, it may cause the following three symptoms.
1. Engine stops at full throttle.
2. Engine hesitates when accelerated rapidly.
3. The engine will not come up to full RPM at full throttle.

If the ‘H’ needle is too rich, it may cause insufficient RPM at full throttle. This
causes carbon buildup on the spark plug.

If the ‘L’ needle is too lean, it may cause the following three symptoms:
1. The engine hesitates when accelerated rapidly.
2. The RPM increases at idling.
3. The engine stops when the throttle is moved from high to low.

If the ‘L’ needle is too rich, the idle may be unstable.
The position of the ‘H’ needle will vary according to air temperature and
field elevation.

If your prop load is too high -or engine is too warm -the problem is going to occur
prop for quick easy rev up to 7500-8000 when cool -on the ground
try a 16x8/ 16x10 as smaller prop

I was using a Scimitar 17x8, but after breaking the one I had, I had to switch to an 18x6 Powerpoint or a Graupner 15x8 3-blade. maybe I was overloading it. The scimitars seemed to not really load the engine all that much and wound up nicely. I have a 16x8 and some 17x8's coming. I'll try all the ideas above. While messing with the Graupner I did find it ran better running a little richer than I had it, but then I ran out of time.