ORIGINAL: Tired Old Man
The method I use of using a high and low RPM to set both needles in their respective control ranges is a fast way to get close to tuned. Do this the first time the engine is run. The high needle will often be very, very close to the desired end result when done this way. However, when you go to the lean side of the low needle (peak RPM in the low RPM range) there will generally be further low needle adjustments needed. What's nice is you have already established where the lean point is because you peaked the low needle. So any further adjustments mean you only go richer, or counter clockwise with the needle closest to the engine. 1/16 turn at a time until you get very close, then even smaller increments. 1/8 and 1/4 turn adjustments are really big adjustments. Half turns are for establishing what the initial positions are before running the first time.
In most cases I do my tuning with a running engine but there are some that just can't be done that way. Those start and stop engines are a real PITA but that's the only way to do them. If you have a carb with needles that angle towards a prop do not EVER try to adjust them with the engine running. You're life depends on not tuning with a running engine under those circumstances. Those that elect to tune an engine with a bottom carb with needles pointing straight out the side must excersize extreme care in remaining clear of the propeller with every part of their bodies, clothing, hair, whatever. Rear carb engines are easy if some planning went into the engine installartion to permit needle access. Side carb engines can be easy or dangerous depending on the way the needles face and prop clearance.
Liability Disclaimer:
With any running engine, you tune at your own risk, and make sure you always have someone else nearby. Like within a few feet.
futura,
I don't post on here too much anymore, I usually just read and try to follow most of the advice. Since I believe you said this was your first gasser, I was wondering if you are using Tygon fuel line, and did you using the correct fuel tank stopper? I'm not an expert like some of these guys, but my thoughts are you have a tuning issue. So these questions are just out of curiosity.
TOM,
I have been following a lot of your advice. I am on my third gasser (DLE 20), and have been successful so far with set-up, tuning, etc. My next engine will be a DLE 55, so whenever something pops up on here, I try and read about it. Anyway, I do have a question for you regarding your statement "Those start and stop engines are a real PITA but that's the only way to do them". That is what I have been doing with my two planes that have cowls, and it is a PITA. Recently, I have had an issue with one of them. So I removed the cowl to make it easier to turn the needles (there a slot cut in the cowl, but I wanted to make it easier), and I wanted to see if everything with the linkage was working properly. I'm not flying with the cowl off, just turning the needles. My engines are running pretty good, and I don't touch the needles once tuned, unless I change a prop size, or some other change.
My question is, will the cowl on or off make a difference in the tuning? And if so, how much difference?
Thanks