Question about a 2 stroke engine...
 

I was recently given a old airplane from my dad. This thing has probably sat for about oh, 10 years. I just got a new radio and receiver for it. I am just having a little problem Fine tuning the engine. I know there is a high and low needle valve. one which controls fuel and the other controls the air.. My question is I have it lean enough to where it almost shuts off if I turn it down to much but I am still getting oil out the muffler. Second when does low needle valve come into play? I can't really rev it full and get good response from it. Any info would be good. Any advice or a thread I missed?

RE: Question about a 2 stroke engine...
 

You want some oil in the exhaust. You don't want to run it too lean; you will ruin the engine. Tell us what fuel you are using (nitro%, oil%) and what engine you are trying to tune. With this info there are many engine experts here to help you.

RE: Question about a 2 stroke engine...
 

The engine says OS-702 Max 25.... And the fuel I am using is called Cool Power the guy at the hobbie shop told me to get it. It don't tell me what the %'s are.

RE: Question about a 2 stroke engine...
 

Adjust the high speed needle valve (big one) until you get maximum RPM with the throttle wide open then richen it (open the needle) slightly so you get a 200-300 RPM drop. You can do this by ear but a tachometer really makes things easy & accurate.

The low speed needle could be either a fuel control type or an air bleed type depending on the engine/carburetor. Regardless, turn it 1/8-1/4 turn at a time one way or the other. Open the throttle to clear it out then bring it back to idle. If it seems worse, you went the wrong way. Adjust this needle until you get a smooth reliable idle and a good throttle response without stumbling.

You can also do a "pinch test" to determine what the engine needs. Pinch off the fuel line going to the carburetor. If the engine speeds up noticeably then quits then the mixture is probably on the rich side. If it just immediately sputters & quits then the engine is likely too lean. If RPM slowly falls off with possibly a slight rise when you first pinch the line then the engine quits, it is likely fine.

This inexpensive tachometer works pretty well: http://www3.towerhobbies.com/cgi-bin...&I=LXPT31&P=ML

RE: Question about a 2 stroke engine...
 

Let me elaborate on what Chuck said...

First, bring the engine to full throttle. Lean the mixture until you hear the engine peak. At this point, make a mental note of where the needle is set. Keep leaning it until you hear it start to sag (This should happen within about a quarter of a turn). Then, richen the mixture again until the RPM drop (Very) slightly on the rich side.

Now, bring the throttle to low. Allow it to idle for about 30 seconds. Does it maintain a good idle or does it die? If it maintains a good idle, rev it back to full throttle. If it does this well, you're ready to go.

If it dies at idle, or if it does not transition from low to high well, then bring it back to idle (Restart if necessary) And before it dies, pinch the fuel line with a pair of pliers. The engine SHOULD run for a few seconds and die. If it dies almost immediately, the low-end mixture is too lean. If it runs for several seconds, the low-end mixture is too rich.

Keep in mind that each time you adjust the low end, you'll need to bring the engine back to full throttle and re-adjust the high end.

Good luck!