I was setting the timing on my son's 90 YJ (4.2) today and noticed something peculiar. I set the timing to 9 degrees BTDC with the vacuum advance plugged. It idled really smooth...sounded better than it has in a while.
When I hooked up the vacuum advance, it started to pop and idle rough. I checked the timing with the dialback timing light and it appears that I've got about 42 degrees of timing with the vacuum advance connected. It's almost like the vacuum advance is pulling full open at idle. When you increase the rpms above idle speed, the timing advances slowly - I'm guessing that it's the mechanical advance operating.
I've got the vacuum advance connected to what I believe is manifold vacuum off of the fitting going to the power brakes. Does this sound right to anyone? Or possibly could I have a bad vacuum advance can?
Thanks,
Jim
When I hooked up the vacuum advance, it started to pop and idle rough. I checked the timing with the dialback timing light and it appears that I've got about 42 degrees of timing with the vacuum advance connected. It's almost like the vacuum advance is pulling full open at idle. When you increase the rpms above idle speed, the timing advances slowly - I'm guessing that it's the mechanical advance operating.
I've got the vacuum advance connected to what I believe is manifold vacuum off of the fitting going to the power brakes. Does this sound right to anyone? Or possibly could I have a bad vacuum advance can?
Thanks,
Jim