need help on engine miss

Everything tight. While looking for a vac. leak I replaced the intake mani. gaskets, but the old ones looked good.
No egr valve.

Hey, Tom. Been rolling this one around for a solution and only have two (remote) possibilities.

Old school taught me that no engine runs without fuel, fire and pressure. Since your pressure and fire seem to have checked out, that only leaves fuel. The cyclic nature of the misfire (always the same cylinders) has me looking for a cyclic fuel problem. The only cyclic component of the fuel system is the fuel pump. If it were cavitating, wouldn't it decrease your fuel pressure at the same point in the firing order? Hence, your two dead cylinders.

The other guess is either a stuck needle valve in the carb or a bent/leaking bowl float. Problem is (although it would account for the fuel shortage) why would it always starve the same two cylinders? I don't think it could, unless there was a supply issue before the carb.

Throw a fresh fuel pump on that baby and see what happens. Wish I could help more.

John

|UPDATED|4/20/2004 1:48:04 PM (AZT)|/UPDATED|

This could be a fuel problem, hence the propane or carb cleaner test. But the fuel pump won't do that. I just supplies enough fuel to the carb. After that fuel just dumps into the float bowl. This elimitates any cavitation problems from the pump. The only way the pump will affect it is if it delivers too much pressure, causing the car to flood, or too little causing a starvation problem, but that would affect all cylinders.

I suspect a vacuum leak or air flow problem in the intake. Back to the propane/carb cleaner test.

Ken, that is what I came up with also. I pulled the intake and inspected it closly, then replaced the gaskets and very carefully put it all back together. No change. I'm going to give it another leak test tomorrow.
Tom

make sure the rockers arn't run down too far and leaving the valves open a bit