OS 40 MAX FP question

That should have read 'small screw on the front of the carb' !

cheers, Len

Yes. The FPs have an air-bleed idle mix control. Opening the screw leans the mix at idle. Contrary to some opinions, I'd start with the airbleed hole almost all the way open. Even then, it might be too rich at idle. If it is, open the air bleed all the way, or drill out the hole the next size up. Dr.1 Driver "There's a Hun in the sun!"

Many thanks but if this is for the idle then why wouldn't it peak out? Is it a question of getting both the needle valve AND the air-bleed set right like the 'mid-range' adjustment on the SC engines?

cheers, Len

There is no real midrange adjustment with most model engine carbs. What you have with a typical two needle carb is a low throttle adjustment and a high throttle adjustment. The low speed adjustment controls the mixture up to about 1/2-3/4 throttle and the high speed or main needle takes over from there.

With the FP, the main needle controls the mixture from about 1/8 throttle all the way to wide open. The air bleed takes care of the over rich condition that this makes at very small throttle openings. If the engine won't peak out, then it is only in the main needle part of the carb.

When you say it won't peak out, do you mean it runs too rich or too lean?

You do have to check the prop size. These are great running little engines, kind of like a grandmothers 4 cylinder engine car. It's a 40 FP it doesn't have much 'peak' built into it... Andy

We can make a box of wood.....FLY!!