Engine tuning
#26
Senior Member
My Feedback: (3)
ORIGINAL: bkdavy
To check your idle mixture, start the engine, then at full throttle, adjust the high speed valve to peak RPM less 300-500 rpm to the rich side. Now reduce throttle to your lowest reliable idle. Let the engine idle for about 30 seconds, then punch the throttle to full. If the engine hesitates, then goes to full throttle, the low speed mixture is rich. If it goes to full throttle without hesitation, your done. If it just dies, your low end is lean. An alternative check is to pinch the fuel line. If there is a slight rise in RPM when you pinch it, your rich. If it dies immediately your lean. If it continues to run for a few seconds without RPM rising, your close. Use both tests.
Now based on your results, you can make a small adjustment in your low end needle. Remember with an airbleed carb, turning the screw out will LEAN the mixture, and vice versa. Make your adjustments in 1/8 turn increments. Then you MUST reset the high speed needle as before and repeat.
Take your time. It might take a few tries to get it dialed in, but once you get it, you'll never have to mess with it again.
Good Luck.
Brad
To check your idle mixture, start the engine, then at full throttle, adjust the high speed valve to peak RPM less 300-500 rpm to the rich side. Now reduce throttle to your lowest reliable idle. Let the engine idle for about 30 seconds, then punch the throttle to full. If the engine hesitates, then goes to full throttle, the low speed mixture is rich. If it goes to full throttle without hesitation, your done. If it just dies, your low end is lean. An alternative check is to pinch the fuel line. If there is a slight rise in RPM when you pinch it, your rich. If it dies immediately your lean. If it continues to run for a few seconds without RPM rising, your close. Use both tests.
Now based on your results, you can make a small adjustment in your low end needle. Remember with an airbleed carb, turning the screw out will LEAN the mixture, and vice versa. Make your adjustments in 1/8 turn increments. Then you MUST reset the high speed needle as before and repeat.
Take your time. It might take a few tries to get it dialed in, but once you get it, you'll never have to mess with it again.
Good Luck.
Brad
Even by doing this your idle mixture can still be way way off which is what I see all the time.
#28

My Feedback: (1)
ORIGINAL: Geistware
I would recommend that all glow engines be set rich initially. That way as fuel is consumed, the engine will run leaner and you must have enough fuel flowing to keep it rich. No engine has been damaged from a rich run.
I would recommend that all glow engines be set rich initially. That way as fuel is consumed, the engine will run leaner and you must have enough fuel flowing to keep it rich. No engine has been damaged from a rich run.
An ABC or ABN engine has a brass cylinder which is fitted tighter at TDC than a ringed or lapped iron motor. If you run it too rich the cylinder won't heat up to get the running fit it needs. You'll prematurely wear the engine out.
Note - it is far more beneficial to run an engine in short 1-2 minute runs then let it cool completely between runs vs. hooking up a 20 oz tank and letting it run an hour.
Best bet is to follow the manufacturer's recommendations - especially in fuel and prop selection. Don't overload an new engine with a too large prop.
I broke in my TT 46 Pro by mounting it on a test stand, put a 10x5 prop on which had been balanced and ran a 2 oz tank of 10% nitro with 20% castor/synthetic oil content fuel (such as Sig Champion). I ran it with the muffler on and muffler pressure (it didn't want to needle without muffler pressure). I started it, peaked it out to get it to heat up then backed off about 1/4 turn of the needle. It was running in a fast 4 cycle and barely breaking into a 2 cycle setting.
My TT 46 Pro is one sweet running engine. I don't even use an electric starter anymore - just choke it twice, hook up the battery leads and spin the spinner clockwise with my fingers. Rotate the prop counter clockwise until it is resting against the compression stroke then smartly twist the spinner clockwise. The prop will act as a flywheel and the engine should fire when it hits the compression stroke but bounce back and start running forward.
#29
ORIGINAL: PipeMajor
It was running in a fast 4 cycle and barely breaking into a 2 cycle setting.
It was running in a fast 4 cycle and barely breaking into a 2 cycle setting.



