I have a 1983 F-150 with a 300 i6 carbed. The previous owner did a hack job on the egr plate and the air pump so no emissions stuff was working. The truck ran OK but had a very small "misfire" every few seconds. Also had a loud exhaust leak.

Today i tore it apart and put a new intake/exhaust gasket. Since the EGR stuff was blocked off anyways i removed the spacer under the carb and just mounted the carb directly to the manifold.

She started right up and I readjusted timing and idle.

It idles faster than it should and It has a constant misfire that i cant get rid of. Also there is exhaust gas coming out near the bottom of the carb. It gets worse when i open the throttle. It also has white smoke out of the exaust now and some of it is coming out of the bottom of the carb. Any idea how exhaust could be getting up to the carb? Could one of the valves be stuck open?

 

If you think it's a valve, you can do a compression check on each cylinder and that will show up.

 

EGR = Exhaust Gas Recirculation... a small quantity of exhaust gases are recirculated back into the combustion chamber via a passageway that the EGR valve controls.

 

I suspect you have a vacuum leak, probably at the point where the carburetor is resting directly on the intake manifold. That would explain the higher than normal idle speed... either that or the accelerator cable is now angled downward and is binding.

When the engine has just started [not yet too hot], with it idling in neutral or park, if automatic, [be careful; use parking brake and wheel chocks], spray the base of the carburetor and along the surface of the replaced intake/exhaust manifold gasket with brake cleaner and see if the speed changes.

If there is a vacuum leak at the bottom of the carburetor, there will be a space where you might get wisps of smoke.