I have a used FS 40 mounted in a cub @ 90'. I have Cool Power 4 stroke fuel, new OS F plug and a MAS 11 - 5 prop. It starts great, revs great but wants to bark, spit and die at lower speeds with the glow clip removed.
What else can I try so I will be able to land this with the engine still running. Now the most reliable idle is too high for a good landing.
I forgot to mention that my engine only has the header pipe and therefore I have no muffler pressure to the tank.
Thanks,

ZB

Jimmy,

I don't have one of these, but it sounds like your mixture is too lean at idle? Doesn't it have the air bleed idle carb? Is there a way you can enrichen the mixture at idle?

Most people don't use 4 stroke fuel in a 4 stroke. They use regular Omega or Cool Power Heli types?

War Eagle, Go Tigers etc

w8ye;

I'm not saying that you are wrong, but I think the low end is too rich.

IMHO, spitting fuel and the tendency to quit when the glow clip is removed both indicate that the low end is too rich...?

Sandal,

You are correct. I must have had a brain fade?

Jim

Perhaps check the valve clearance. May be loosing compression?

Hello!
I run one of these OS FS. 40 20 years ago ,it was a fine performer, As a matter of fact I still have one of these new in box, never run.
At sea level were I fly I used 5% nitro and 20% castor oil (of course an OS F plug) and an 11x6 APC prop. If you fly at sea level I would think the 11x5 is way to small for this engine. I used my Os in low winged airplane designed by myself with a span of 160 cm weighting 1,8kg and I could nearly do vertical takeoffs using the above combo.

Regards!
Jan K
Sweden

HELLO ZB50,IM HAVING THE SAME PROBLEM WITH A OS 120FS IF YOU FIND OUT PLEASE LET ME NO. EDDIE