V-Twin Forum banner

1 - 3 of 3 Posts

·
Registered
Joined
·
46 Posts
Discussion Starter #1
what does everyone use for a tach to set there idle for setting the timing. i have a auto digital tach but i can only turn it down to 4 cylinder. i devide that rpm in half but it doesnt sound right. my bike, when cold, idles on the digital tach at 900 rpm, which would be 450 rpm, but when i check my timing it is right on, then when it warms up the tach says 1400 rpm, which would be 700 rpm, the idle then seems just about right or a little fast. at 900 rpm on the digital tach the timing is right on and at 1400 it shows between 35-40 degrees advanced.
 

·
Banned
Joined
·
871 Posts
hotrod351 said:
what does everyone use for a tach to set there idle for setting the timing. i have a auto digital tach but i can only turn it down to 4 cylinder. i devide that rpm in half but it doesnt sound right. my bike, when cold, idles on the digital tach at 900 rpm, which would be 450 rpm, but when i check my timing it is right on, then when it warms up the tach says 1400 rpm, which would be 700 rpm, the idle then seems just about right or a little fast. at 900 rpm on the digital tach the timing is right on and at 1400 it shows between 35-40 degrees advanced.
I wouldn't trust your timing light's tach on a V-twin. They are designed to work with 4 cyl and up. Just dividing the number by half won't work. I'm sure there's a different calculation to use to figure it for a 2 cyl. engine.

If you have a tach on the bike, just use that one. It's accurate enough for setting idle speed. If you don't have a tach on the bike, they take it to a shop that has the correct external tach, or set it by ear. If it sounds like it's lugging, it's too low. It's better to have it a bit too high than low, becausing too low an idle will wear your engine out a lot faster that it should.

Your timing sounds good. I never use a dial-back timing light... no need to. I just set it statically, then check it again at idle. If I rev the engine and the mark moves, then I know the advance is working. No need to get more into it than that. If it's not some high-dollar, high rpm race engine, and it's running right, you are close enough.
 
1 - 3 of 3 Posts
Top