I am having some problems with my OS 46 FX and GMS 47 and I think the problem is me. They both start ok and run and transition pretty good on the ground. But when they are both in the air, they seem to "sputter" between about 20% and 80% throttle. Above or below those ranges and they are both fine. I am using 10% fuel with 18% oil and varying props (which does not help or hurt). I am thinking the problem is adjustment since they are both doing it. Do engines act differently on the ground than they do in the air? Any ideas? Thanks in advance for any assistance.

Sounds like you may be a little rich on the high end. Do you have a smoke trail? If so, is it a heavy smoke trail? Is the engine new? I'm reffering to the FX.

It does sounds like you are running it on a rich side. Did you tried "pitch" test?
Also, you are saying it transitioning nice on the ground... Did you move a throttle stick slow or fast? You should move the stick fast and engine should transition smoothly...

I do not see much of a smoke trail. They are both new and have about a gallon of fuel total run through them. By the pitch test, I am assuming holding it vertical. I did try that and the OS sputters once or twice but is otherwise fine. The GMS was fine. As for transition, I did move the stick pretty fast. The GMS transitions pretty good. The OS sputters a bit (only the first time) and then is fine (I think this may also be to rich at idle).

Try this, when you remove the glow ignitor from either engine, What Happens? Does the rpm decrease or stay the same!!!!! If it stays the same your are about on the money for low speed idle. If it decreases you are too rich, begin turning your low speed idle in about an 1/8 of a turn at a time. using the glow ignitor by attaching and then taking it off, checking your rpm. If it does wierd stuff surges, then you probably have a bad glow plug change it. Then do this procedure again. After you adjust the low end retune the high speed needle and check low speed again to be sure nothing is out of whack. Have fun flying!!!
wra

If his engine is sputtering while transitioning, its the LOW end needle, not the high end needle valve that is too rich.

Key words when in the air, if he leaned it out on the ground. Then it is even leaner in the air. Chino ole man. So, he needs to richen it, it probably predetonating.

I flew the OS today today and leaned the low and top end and it seemed to help. I should also mention that the weather is getting colder here in Ohio, and I think that is part of it. I will try to richen it and see what that does. Thanks for everyone's input.

I've always found that the best way to adjust the fuel mixture on the ground is
to rich it up at full throttle until the engine four-cycles, then lean it out to
the point where the four-cycling just stops. That, in the air, the fuel mixture
is just lean enough to run correctly.

This may sound like a stupid question, but how can I tell when the engine is four-cycling?

Dean:

It's not a stupid question, it's a term you're not familiar with.

As you adjust the needle rich from a full throttle peak, at a certain point you will notice a marked change in the engine's sound. That's the "Four stroke break."

HTH.

Bill.

It's easy to hear - when the engine stops making a clean howl, and instead makes a sloppy sounding buzz,
it indicates that the engine is only firing on alternate cycles. It's possible to find a spot on the needle adjustment
where the engine may switch back and forth between howling and buzzing. That point is still too rich.