Small Engines (Lawn Mowers, etc.): fx class racing mower 290 clone, lawn mower racing association, rod rest

Question
my racing mower engine stalls out between full throttle and 3 quarter throttle under load I've changed from 3 different carburetors with no difference , has an arc flywheel and arc rod, rest of aging is basically stock.... what solutions could I use different., how about changing ignition coil burhans good blue spark so I didn't. flywheel is adjustable and have adjusted plus and minus before and after top dead center with no difference ..... please help if you can... thank you mark davis etowah,tennessee..... member of east tennessee national lawn mower racing association...bp838 andfx838

Answer
Have you went larger and smaller on the carb.  Sounds like the engine may be starving for fuel.  
You mentioned it stalls under load...what about on the bench?

Is there any way you can introduce extra fuel when under load just to see if the engine is starving for fuel?

Igntion timing may be a factor but not likely; same for the coil.  

What carb are you running?  Can you make the carbs high speed circuit larger by drilling out the high speed circuit?  I suspect this would be very, very difficult.

Eric