Hi Bill,

a friend of mine has an ST, think it is a 2500 same as mine in his large Spitfire. The engine has always run sweetly till just now. I was on the phone to him and he was saying that it will idle fine but as soon as he advances the throttle it backfires and throws the prop.

He has been flying STs for 25 years and he is baffled.

appreciate any advice you can give.

thanks

cheers
Peter

If the engine idles fine, but tends to backfire and throw the prop when the throttle is advanced, the usual difficulty is that the idle mixture is just too rich. Please see the article at the top of this forum to see how to set up a SuperTigre carburetor. You want the idle mixture as lean as possible yet still giving good acceleration.

Bill,

correction. It is actually an ST3250 with OS carby fitted. Ron said he had run the engine with no problems about 2 months back.

I'll tell him about the idle mixture as that should be a consistent problem regardless of carb fitted.

Once more thanks for your advice.

cheers
Peter