I have an OS Max 40 FP engine that I purchased back in 1989. I used the engine 5 or 6 times and parked it until this year when I decided to get back into flying. The engine cranks right up and idles. I rev the engine up and it wants to run on the lean side 1 1/4 turns. When I return to idle and rev the engine back up it shuts off. I have tried running it rich and have adjusted the air bleed screw from one extreme to another in 1/4 turn increments with no luck. The engine runs with no problems at all if I leave the glow plug igniter on. Any ideas?
Fuel Tower Power Premium 10%
#8 Glow Plug (New)

Change to a #3 OS plug

If the engine sat for 6 yrs or so I'de check all the seals and gaskets first carb and backplate. Then i might have to get serious and try more extreme measures like a hobby guy or friend that knows engines. I say check all seals and gaskets first as this seems to happen after it has time to warm up and everything expands when it's warmed up a bit. Could be an air leak somewhere.

Thanks,
I haven't noticed any leaking from the back plate/ head or carb . However, I did see fuel at the crank shaft/Crank case and the drive washer. Would this be normal if it was getting too much fuel? What sign do i need to look for for bad gaskets?.

OS doesn't make a #3 glow plug. They make an A3 and a P3. Now Enya makes a #3 and this is an excellent plug. I use them in all my glow engines.

If an engine runs well with the glow driver attached but slows down or quits when the driver is removed it indicates one of two things. Either the plug is too cold or the nitro content is to low. An OS#8 glow plug is not too cold so his plug is fine unless it's worn out. He didn't say how long his fuel had been sitting around or what nitro content it had. Old fuel could be contaminated or some of the volitiles might have evaporated. This would make the engine perform like he describes. I would use at least 10% nitro but they will run well on 5%. Start with a new can of fuel and a new OS#8, A3 or Enya #3 plug to eliminate all the obvious potential problems and work from there.

First disassemble the entire carb body and needles looking for cracks in the silicon seals, the black 1's . check them closely. I don't have the manual but there might be a small 1 on the high speed needle or both.

Try some fresh fuel, it sounds like your fuel is stale. You have of course
tried a new plug ?

FBD.

Hi!
The OS line of FP and LA engines are very user friendly and need hardly any any adjustments on the air-bleed needle to function extremly well.
They throttle and run perfect from the start if you just follow some simple rules.
And here they are:

Use fresh fuel containing 5-10%nitro...15% is over kill!
Use an OS 8 or Enya 3 glowplug (There are many other god plugs too).
Use a 10x6, 11x5 or 11x6 prop. Preferable APC, RAM , Bolly or Graupner.
Use a 240cc (8oz) fuel tank with it's center line inline with the carb when plane sits horizontal (very important).
Do not use a cheap plastic spinner without a backplate. Instead use an aluminum spinner nut.

If you do the above and just set the engine a little rich your engine will run and throttle just fine.
But if not you must check the backplate screws, head screws, carb, fuel and glowplug.

Regards!
Jan K
Sweden