Originally Posted by
Flanno
Richen the top end an hour or two.
The pinch test when cold to warm is a guide only to get you close and is a 2 part test, 1- how high it revs just before it dies tells you where your idle gap is set and 2- how long it takes to rev up and die tells you how rich or lean it is.
When engine is up to temp or close to it, rev the engine a few short times in short bursts to clear the engine then hit the brakes, listen carefully to the idle, if straight away it is idling high and then drops after a second or more then it's an average woman tuned bottom end.
Idealy you should be able to clear the engine and hit the brakes and the engine should sit and idle with no drop in revs for at least 25 sec and even then it will only be a slight drop.
With very small adjustments each time,
!; lean the LSN and clear the engine and apply the brakes and start counting while listening closely to the revs to see what it does, if it drops quickly repeat step one untill it takes atleast 7 sec to drop.
2; then reduce the idle gap a little and clear it again and see what happens,
keep repeating step one and 2 untill it sits idle for more than 25 sec with no drop or raise, if idle is irrataic and raises then you are a little lean on the bottom and have gone too far.
I know what to listen for etc in person and what step to take, but it's hard to put into words on here, but I hope that helps.
Too true mate, small adjustments, and a good ear is worth a thousand fingers.
A little off RC tuning, but same principals apply:
Taught chain saw and whipper snipper tuning for many years as a TAFE Teacher.
Would show classes how to tune same, asked them to take note of the engine sound, make sure they had it "right", then send them of to lunch.
During lunch, I would turn the low speed needle in 1/2 a turn and then would ask students to start their respective engines. After pulling on the cords and getting blisters, with no start, they would admit defeat.
The point here is, if needed, go back to original settings (or factory recommended) , return from there, SLOWLY, and listen to what the engine is trying to tell you.
Yes it doesn't happen overnite, but if you really concentrate on developing a good ear for engine tune, it certainly helps.