dkshema
rrProfessor
Location: Cedar Rapids, IA
| Set the top end by starting the engine and adjusting the high speed needle first. After you get the high speed adjusted, go for the idle.
I've never had much luck with air bleed type idle settings.
As you screw the screw in, you're richening the idle mixture, as you screw it out, you'll be leaning out the idle mixture.
You're going to want to try to get the idle needle adjusted so that:
A. the engine will idle at a reliable low rpm (a lot of people try to just idle the engine way too slow).
B. Transition from idle to full bore smoothly.
For the idle, if you let the engine sit at idle and it slowly slows down and dies, the idle is too rich, and you need to open up the idle screw. If, on the other hand, the engine at idle slowly increases in speed, and dies, the idle is too lean, you have to turn the screw in a bit.
If, after the engine sits at idle for a while, and you suddenly open the throttle -- the transition to full power should be smooth, and nearly instantaneous.
If the engine spits, sputters, and then dies, the idle is too rich, and you need to lean it out some. If, on the other hand, the engine just plain stops, without spitting and blubbering all over, the idle is too lean, you need to richen it up.
I've found that the air bleed hole is generally too small to do any good. I have a fairly new OS 46LA that until last spring, I was willing to give it to anyone who asked -- simply because it ran like crap. I finally used a 3/32 inch drill to open up the bleed hole in the carb, and now the engine runs exceptionally well for a cheap bronze bushed, lapped piston engine.
You may have to resort to drilling out the bleed hole in your carb for the idle setting to really have any effect. If the screw is backed out all the way so the bleed hole is open, and you're still too rich on idle, you'll need to drill out the hole a bit. Be careful doing this.
I assume you've got a muffler on this engine, and that its pressure fitting is connected to the vent line of your tank so that you are using muffler pressure to insure a positive fuel flow. Your tank centerline is also going to want to be about the centerline of your needle valve too. If the tank is too high above the needle valve, you'll be rich a lot, if the tank is too low, you'll run lean a lot (and if you're doing rolls or loops, the engine will go from lean to rich or rich to lean as you change tank positions).
Dave |
