os 75ax
07-13-2009 | 09:49 PM
#1
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From: , VA
os 75ax
I purchased a 75 ax for my 60 sized trainer after original engine 65 LA was damaged in a crash. engine has been ran about 10 flights and ran great but now im having some problems at half throttle engine starts to break down and will start to stutter if you go above half throttle engine smooths out and at idle runs fine engine also transitions from idle to full throttle great . when air plane is inthe air it will actually go from half throttle to the point of stalling then come back
and then i get scared and land because i just learned to fly and I like to land under power. Several people that have been in this hobby for a long time have tried to help me and adjust the needle valve and the mixture valve but i t doesnt make any difference I took the engine apart and there is no piston or cylinder damage I packed foam around the fuel tank to make sure that there was no foaming in the tank. I am running a smaller prop than reccomended in the manual 12x8 because of ground clearance issues but i flew it with this prop succesfully the first 10 flights im using a 15% nittro fuel
and then i get scared and land because i just learned to fly and I like to land under power. Several people that have been in this hobby for a long time have tried to help me and adjust the needle valve and the mixture valve but i t doesnt make any difference I took the engine apart and there is no piston or cylinder damage I packed foam around the fuel tank to make sure that there was no foaming in the tank. I am running a smaller prop than reccomended in the manual 12x8 because of ground clearance issues but i flew it with this prop succesfully the first 10 flights im using a 15% nittro fuel
07-14-2009 | 09:48 AM
#2
My Feedback: (11)
RE: os 75ax
You could have a bad plug. Try an O.S. #8. That's a good one for 15% nitro fuel. You could also have a rather rich midrange. Likely, the idle mixture is a bit too rich.
To set a carb, you need to start out with the idle mixture too rich. Open the high-speed needle 2-3 turns out from closed. Start the engine at 1/4-1/3 throttle, and open to full once it starts. Lean the high-speed mixture a bit to get the engine at a higher RPM, and then remove the starter battery. Lean the high-speed mixture to just rich or peak RPM. If the engine will run out a full tank of fuel with little mixture change, you can set up the idle. Retard the throttle to about 1/2 and adjust the idle mixture a bit. Retard and adjust some more, a bit at a time, until you get a good idle. You should be able to idle at 2,500 RPM or below.
If the engine hesitates and then picks up when you gradually open the throttle, the idle is likely too rich. Lean it a bit and then change the idle RPM so that you have a good idle. Remember, when you change the idle mixture, you'll have to change the idle RPM. Many times, you can get a very good idle at a very low RPM, but you'll have a lousy throttle transition. You'll have to trade some RPM to get a better transition.
To set a carb, you need to start out with the idle mixture too rich. Open the high-speed needle 2-3 turns out from closed. Start the engine at 1/4-1/3 throttle, and open to full once it starts. Lean the high-speed mixture a bit to get the engine at a higher RPM, and then remove the starter battery. Lean the high-speed mixture to just rich or peak RPM. If the engine will run out a full tank of fuel with little mixture change, you can set up the idle. Retard the throttle to about 1/2 and adjust the idle mixture a bit. Retard and adjust some more, a bit at a time, until you get a good idle. You should be able to idle at 2,500 RPM or below.
If the engine hesitates and then picks up when you gradually open the throttle, the idle is likely too rich. Lean it a bit and then change the idle RPM so that you have a good idle. Remember, when you change the idle mixture, you'll have to change the idle RPM. Many times, you can get a very good idle at a very low RPM, but you'll have a lousy throttle transition. You'll have to trade some RPM to get a better transition.
