>Does the Compression play a roll?
It's about 10% more efficient to burn the fuel at 10:1 than it is to burn
fuel at 5:1 compression. As long as you have at least 90 psi cranking
compression, the engine should start.
>The manual (xt550 '83) say it should
>be 156psi, I only get about 130psi (wet/dry).
Your valves are burned or not seating well for some other reason, such
as a build up of carbon.
>What is the tolerance on that.
130 psi is about the minimum.
>My tester can't be 100%, because it works with a rubber end
>on the sparkplug hole (at a place where you can't see nothing!)
OK, there is some extra volume inside the compression tester and the tube
connecting the tester to the spark plug hole. That's why you cannot get
a full pressure reading the first time the piston comes up on compression,
have to kick the engine through about 20 to 25 turns so you get 5 compression
There is a tire valve inside the rubber end of the tester to capture a
of the pressure from each compression stroke.
The pressure should rise evenly, the same amount for each compression stroke.
But using one of those testers that doesn't screw in makes compression
Also, the test is supposed to be done with the engine warmed up and the
so the engine can get some air to compress.
>much compression do I loose with the automatic compression release,
I dunno, do you hear the compression leaking out the exhaust when you
kick the engine over?
>will it help to disconnect that?
It would make sense to disconnect the cable.
>How do I know if I have a low voltage coil?
The spark from low voltage coils would only jump about 1/4 of an inch. Higher
voltage coils make long sparks, but you risk having the spark jump from coil
to coil *inside* the coil, ruining it.
>Where do you kick from? TDC, pre-, post?
It doesn't matter what position you start from. You have to kick and kick and
kick continuously while holding the compression
tester in one hand and the throttle open with the other hand. You need to
engine through about 20 to 25 turns.
When the compression stops rising, you've trapped all the pressure inside the
that the engine can produce in 4 or 5 compression strokes.
Message posted via MotorcycleKB.com
http://www.motorcyclekb.com/Uwe/Forums.aspx/yamaha/200708/1 >> Stay informed about: Hot vs Cold Start