How do you know your engine is running just right using a techometer? Lets make beleive we are checking a OS.46 engine. How do you know? We also wanna make sure were running a little on the rich side so we dont hurt the engine by running too lean.

Use the tach to measure the rpm. then lean (clockwise) the HS needle valve by a few clicks - about 1/8 turn. check the rpm again. keep doing this until you find the maximum rpm. Then open the needle valve until it slows down a few hundred rpm. Now you have used the tach to properly set the veedle valse. Most of us can also do this "by ear", but the tach makes it more scientific and more fun. Other uses are to compare things. For example, you want to compare your fuel to your buddies fuel. You tach the engine running your fuel (suppose it has 10% nitromethane). Then you tach it with everything the same (same prop, etc.) but using your buddies fuel (suppose it has 15% nitro). Now you can determine if the extra nitro makes any difference. (usually this will increase the rpm by a few hundred, by the way).

Start your motor and lean it out with the high speed needle valve until you get the highest RPM's you can get then richen it up until the RPMs drop 200 to 300 RPMs then your set.

One quick method that my instructor taught me was to run the engine at full throttle (airplane obviously restrained), then turn the high speed needle counter clockwise slowly until the engine goes from two stroke to four stroke (engine will slow RPM and make a distinctive change in the way it sounds). Turn the needle valve clockwise a bit and then quickly pinch the fuel line with your fingers. If the engine RPM goes up then quickly goes down once you remove your fingers, it is probably ready. Try this against the tachometer to see where that engine "note" changes then, eventually you will use your ear rather than the tach. It takes practice to get that right, but it works just fine. Not that the tach method does, not, just that it is an alternative to using the Tach.

With my 46FX engine with an APC 11-5 prop I adjust for max rpm and then richen by 3 clicks. This consistantly gets me 14,200 rpm. If I get less, then somethings wrong. Funny thing is with my 40FX with an APC 105 prop I also get 14,200 rpm on that engine. I don't know if its different at other elevations or not but thats what I get at my location. When I read about how other flyers like their engines because "it screams" doesn't mean anything to me. Tell me how many rpm you are getting and what prop you are using then I might be impressed![8D]

I like using my buddies fuel! [8D]

Yeah, right!

After you use a tach for a while you soon realize that all engines are not created equal. You also learn what rpms you need with different size props. The TT 42GP engine will give you 12000 rpm with a APC 10-5 prop which will give you a decent takeoff speed. There was a new guy with a bad engine on his trainer. With a 10" prop on his plane we could only get 10,500 out of the engine. It was barely enough to get the plane off the ground on our grass field.[8D]

I'm a sport flier, I don't race, at least not formally. My goal for setting the needle is good performance, no dead sticks, and slightly rich to promote long engine life. I don't use a tach for setting the needle on 2 strokes. I do use it for 4 strokes, and I also use it to compare props. I find the peak rpms by leaning the needle until I find the peak and then I richen it until I can hear the engine slow down a bit. Once I've done this I hold the plane with the nose in the air 5 to 10 seconds. I do this to confirm 2 things. The first is that it's not too lean. The second is to be sure the muffler pressure helps the engine get enough fuel while it's vertical. I expect the engine to speed up a bit when I first hold it vertical and then hold that speed. If it slows down, I know it's too lean.

Something to remember is that engines will get a bit leaner in the air and will continue to lean out as the tank empties. I feel that taking off close to peak performance is an invitation for a deadstick and short lived engings.

Piper.. that's exactly what my instructor taught me, but we use the pinch the fuel line way to see where the needle valve is set. I get the same either way so I feel that both methods work and work well. I also like keeping that mixture a tad bit rich, again, for both reasons you said, prolong engine life and because the engine will run leaner in the air as the tank empties and as the aircraft goes vertical.

I've seen deadsticks, not long after takeoff, from people who used just the pinch method. A couple concerns about it are that the length of the pinch can be inconsistant, and it doesn't confirm that the engine can draw fuel while climbing. I've used it occasionally, but follow it up by holding the plane vertical. Just my opinion, your experience may be different.