jrsaoe

I have inherited an asp two stroke .91 that has great compression but will not run past half throtle. I've messed with the needles all day and think that it is simply gunked up on the inside. What would be a good way to clean it out? Also it is an earlier generation of the asp motors i believe it has a red head on it.

Flyboy Dave

My Feedback: (21)

You can remove the high speed needle, and give the inlet a blast with some
carburetor/choke cleaner, available at the auto parts store.

FBD.

Sport_Pilot

Some people will assume the engine is running lean when it detonates as it has poor power and does not run right. If thats the problem then you are using the wrong fuel. It will detonate badly on any fuel with 10% or more nitro. Use 5% or less. As hot as it is now you may want to use 0% nitro.

delman

I have an OS 91 FX that did that - a new glow plug fixed it. If you still have the problem try a tank of somebody elses fuel to make sure yours is ok.

jrsaoe

Is it common to run below 5% nitro in a 91 two stroke. Does the higher nitro make the combustion happen prior to the piston reaching the top of its stroke thus making it crap out? Does anyone know muhc about this particular engine/ have you ever had one?

w8ye

My Feedback: (16)

The Red Head came with extra head gaskets to lower compression

Flyboy Dave

My Feedback: (21)

I have the new series ASP .91. I run it on 5% nitro. I initially ran it on 15%
nitro, and it detonated so bad, I thought it was going to blow apart. It
blew two new plugs as well. It likes a cold plug due to the high compression.

Mine didn't come with any extra head gaskets. It uses a small prop.
Mine is the OS/Magnum/ASP clone style engine.

FBD.

jrsaoe

So with the 5% nitro i would prop down to something like a 13-6? it has a 14 8 on it, that is what it came with.

Flyboy Dave

My Feedback: (21)

I don't know what to prop the early engines with....

....the new ones won't pull any props worth a hoot.

Sport_Pilot

I have that same engine. I have to use a pump with it as the carb is oversized and will not draw fuel well, and the plane is meant for a .60 so the .91 tank is way too low. I understand they run well with a normal tank location, IF THE STOCK MUFFLER IS USED! With a pitts muffler their is not enough muffler pressure, I understand some are successfull if they plug one of the two exhaust stacks. The carb is the same as the 1.08 carb and is oversized for the 1.08! I can get away with 10% nitro in the winter but in the summer it will detonate on anything but 5%, and on one record breaking hot day it detonated on the 5% without richening the mixture some. It turns about 11,500 with a 13-6 and just under 11,000 with a 14-6. With a slow flying Bipe I would consider a 15-4.

wcmorrison

My Feedback: (2)

If it is an old engine, have you checked the valve clearances? If the valves are very far off it will not run well either. The clearances are .04 to .1 mm. To tight if a .04 will not pass through the gap and to loose if a .1mm
passes through the gap. Set to the .04 side. Do it at room temperature.

I would start with a 14 X 6 or a 13 X 8 prop. And yes a new glow plug and fresh fuel. Low nitro like the man said.

Cheers,

Chip

Sport_Pilot

Ahh? This is a two stroke engine.

jrsaoe

I talked to the engine guru at my field and he said that the motor is not even fully broken in, i guess there is some binding at the top of the stroke so the piston is still rubbing against the top. He said use 0% or 5% and a smaller prop. It could be that with the 15% the motor just got too hot and died because of that. I will try a cooler plug too. I put the cowl on the plane today and it looks badass. The plane is older than i am, haha.

jrsaoe

hey sport pilot is that a foker d triplane (i think that is what it is called) A buddy at the field just maiden on of those. Looked great in the air.

Sport_Pilot

Yes a Fokker DR 1 triplane. Its powered by a TT .91 four stroke to keep this somewhat on topic.

jrsaoe

I got the 5% nitro (is 29% castor oil too high?) and an a5 plug and ran the motor. I was able to get it to optimum rpm with a 14-5 wood prop and to transition from idle to top end without any bog down. I will keep you guys updayted on how it runs and if it pulls that bipe around.