Microlighters

I have a problem on one of the 503 SI engine. After take-off she is running fine on full power, but after the second circuit ( +/- 5minutes) when you apply full power, the engine would not rev to maximum, there is no revcounter but i guess the drop is about 500rpm. It is like it is just holding back with a very very slight surge. I have changed jets, to 155 from 150, replaced the needle and needle jets, carb gaskits and o rings, changed plugs and the fuel filter. I have also checked that both carbs open up equally. the mixture is now set to 3/4 turn out from 1 and a half turns.
Is there anything else i can check before sending the engine in?
Thanks

Hi Vincent,

Don't want to make you negative, and please get some other info as well before doing something drastic that will cost lots of money.

Here is my story. While I was doing my solo training, and doing just curcuits, my plane was also on full power on first take off, and there after it lost power. My power loss was much more radical than yours, so your problem is maybe on the beginning.

Anyway, problem was that the piston was cracked, and that upon 2 take off when the engine was nice and hot, the hole just seem to open up. Had to change a piston. Don't understand the theory behind it, but just make sure that everything is tight, and that no extra air is being pumped into chamber to make your aerie run lean. Also becareful of those 150 carburetor jets, they can make your problem worse if you don't have CHT or EGT on plane.

My advise, Get help from someone just to check that every thing is ok. Better safe than sorry.

Regards,