Greetings from a first time user of this forum. I have a freshly rebuilt engine for my 1930 Model A coupe that I bought as a barn find for $800 three years ago. I am rebuilding to pure stock except for the Mitchel overdrive that I treated myself to. I can't get it to consistently run smoothly and have tried everything I can think of to solve my problem to no avail.
What I've done: changed head gasket twice; changed manifold gaskets at least twice; flow tested existing Zenith-2 carb jets then purchased a new set of flow tested jets from Dave Renner; checked compression and found no compression in cylinder #2; checked all valve clearances and re-checked compression; with no gain in #2 cylinder I adjusted intake valve in cylinder #2 to approx .016" or more from .013" just to see the results; the compression in #2 came up to 60 psi, (this didn't make sense to me since I adjusted the intake valve and not the exhaust valve); all 4 cylinders are reading 60 psi plus or minus 4 psi.
What it's doing: starts easy; when cold it runs pretty smooth initially, then as it warms up it starts back-firing regardless of my spark adjustment position. Adjusting the GAV has some affect, but doesn't smooth things out.
Other interesting notes: I checked the vacuum through the intake manifold port used for the windshield wiper motor. The gauge was all over the place and truly unreadable. I pulled the vacuum gage from the manifold hole and the engine increased rpm's noticeably and ran much smoother. This didn't make any sense to me either. If I plugged that hole with my finger the engine wanted to run rough and die. Eventually the engine backfired through that hole to the point where I shut it down. My brain says there shouldn't be any positive pressure escaping the manifold hole for the wiper motor, it should be sucking, not blowing. I've scratched my head until I have bald spots in my hair, and tried everything I can think of except taking up cigarettes. Is smoking still considered harmful to ones health??
Any ideas from you experienced guys or gals in the crowd? I'm all ears.
Steve Morris
Roseville, Ca.
What I've done: changed head gasket twice; changed manifold gaskets at least twice; flow tested existing Zenith-2 carb jets then purchased a new set of flow tested jets from Dave Renner; checked compression and found no compression in cylinder #2; checked all valve clearances and re-checked compression; with no gain in #2 cylinder I adjusted intake valve in cylinder #2 to approx .016" or more from .013" just to see the results; the compression in #2 came up to 60 psi, (this didn't make sense to me since I adjusted the intake valve and not the exhaust valve); all 4 cylinders are reading 60 psi plus or minus 4 psi.
What it's doing: starts easy; when cold it runs pretty smooth initially, then as it warms up it starts back-firing regardless of my spark adjustment position. Adjusting the GAV has some affect, but doesn't smooth things out.
Other interesting notes: I checked the vacuum through the intake manifold port used for the windshield wiper motor. The gauge was all over the place and truly unreadable. I pulled the vacuum gage from the manifold hole and the engine increased rpm's noticeably and ran much smoother. This didn't make any sense to me either. If I plugged that hole with my finger the engine wanted to run rough and die. Eventually the engine backfired through that hole to the point where I shut it down. My brain says there shouldn't be any positive pressure escaping the manifold hole for the wiper motor, it should be sucking, not blowing. I've scratched my head until I have bald spots in my hair, and tried everything I can think of except taking up cigarettes. Is smoking still considered harmful to ones health??
Any ideas from you experienced guys or gals in the crowd? I'm all ears.
Steve Morris
Roseville, Ca.
