Sputtering idle on OS 55AX.
 

Hello all,

I'm having some issues on the idle of my OS 55 AX engine and I was hoping someone could help me troubleshoot it. I'm running 10% nitro and an APC 12x6 prop. I belive I have both needle valves set correctly. The issue is with the idle. When I have it on the ground and go from full throttle down to idle, the engine seems to sputter for about 10 seconds and then transitions to a nice smooth idle. If I throttle up again and then back down to idle the same thing happens again. I tried flying it but deadstick. I don't know if I'm getting air into the line or if something else is the problem. The tank in this model is rather large (14oz), so maybe that has something to do with it. There is also very little room for foam between the tank and the frame so I had to use 1/16" wing sealing tape. Maybe it isn't adequate.

Anyway, I'm considering decreasing the tank size to 10oz, adding more foam, and switching out the filter for a different one. Other than that I'm at a loss. Any thoughts or suggestions would be appreciated. This is actually my first OS engine, so I'm alittle disappointed that it is problematic. I hope the solution is something simple.

Thanks in advance for your help.

RE: Sputtering idle on OS 55AX.
 

your low end is definitely rich, try going in half a turn, you'll know if you went to far if you throttle up and it dies

RE: Sputtering idle on OS 55AX.
 

I agree, sounds like a tuning issue.

I have not used foam on any plane since my trainer and never had a problem.

55AX is a great engine.

RE: Sputtering idle on OS 55AX.
 

Check for a kink or restriction on your muffler pressure line. Try replacing the glow plug with another OS#8.
By the way the 12X6 is large for it. Yeah I know what the instructions say. That prop is good for noise reduction, but it will only let the engine rev so far and not into it's peek power range. Try a APC 11X6 or 11X7.

RE: Sputtering idle on OS 55AX.
 

I'd say the idle mixture is rich. If you are using a check valve in the muffler pressure line, remove it. I agree with freaking fast. A kink in the muffler pressure line could act like a check valve not allowing the tank pressure to drop right away causing the mixture to be rich until it does.

RE: Sputtering idle on OS 55AX.
 

Hi guys,

Thanks for the responses.

I had actually leaned the low out to withing 1/8 turn of it outright stalling, so I think I'm okay with that.

I did swap out with another #8 glow plug, and that didn't seem to make a difference.

I do have a filter between the muffler and the tank. I'm planning on removing that. I'm also planning on using a different filter between the tank and the engine. I tried a different type than I normally use, so maybe it has a leak in it.

Finally, there is no kink between the muffler and the tank.

Is it possible that the tank is just too large and it takes longer to pressurize it when going from high to low end? I'm swinging by the hobby shop today, so I am going to pick up a smaller tank and some new filters to try them out.

Thanks,
ptux

RE: Sputtering idle on OS 55AX.
 

The tank pressure doesn't go up from high to low, instead it drops. But thats ok because the carb suction goes up. If you have a check valve or kink in the line then it would prevent the tank pressure from dropping, causing a rich idle mixture.

RE: Sputtering idle on OS 55AX.
 

Hi ptuxbury, were you able to fix your problem? I am interested since I have a 55AX as well.</p>