I have a G- 38 that I am running on 100 av gas at 40:1 and 18x6-10. and getting 7200 to 8000 rpm depending on the weather. The last few times that I have flown, at about 4 minutes into the flight the engine starts to sag, get it on the ground and check rpm it has lost between 1500 and 2000 rpm . (been flying thes bird for 17 years sacound 38)

First thought was lean so gave the hi needle a full 1/4 turn rich, seemed to help just takes longer. with another 1/8 turn it goes rich and come up to speed, tryed leaning the low speed needle 1/8 no help there.

Have now checked carb and cleaned (did find some gravel in the screen about 10 granes), back in the air and the same thing, at about 5 minutes it still sages off back to the ground it has lost about 1500 rpm at top end.

So has any one got a clue of what might be the problem, outher than the nut trying to run it.

I have a Poulan 46 that kind if acted like your saying. Wouldn't hold tune to save my but. Constantly retuning the carb. I replaced the ring( I noticed a drastic drop in compresion the more it warmed up) with one from Frank Bowman, broke it in for about 3 to 4 hours then reset the carb and all problems were gone.

Hay Eagle Flyer

Like your thinking, but it seams to have fair compresion when worm (after flight), but I have to admit that would be a cheep fix, so will check the lhs and see if they have a ring. Will run tomarrow and try a little eather around the base of the carb and iso block to see if I might have an air leek, that I cant see..

Thanks

Bob T