Engine miss

[Dozerman51]

Hi all,

While swapping out my Dodge head for the 58 Plymouth head I plan on checking my valves. I have a miss at Idle. It does not miss at high speed. I have a vacum reading of 20". The needle is not steady, but only wavers 1/2-1" of vacum. The cylinders read 110 all across. It does not smoke, stall out , overheat or use oil other than the leaky god foresaken rear main seal. I rebuilt it 22 years ago using all new parts except the valve springs. I have about 20,000 miles on the motor. Any Ides? I also will have the fender and splash off the truck while working on the valves and head. Is it possilbe to do an Inframe porting job on the block? Thanks for any advice?

[aero3113]

Could it be just a carb adjustment?

[Dozerman51]

Hello aero3313,

I tried the carb adjustment; it didn't help. The mixture adjustment works since I can kill the motor by screwing in the adjustment. I set the carb to the maximum vacum reading. Wonder if it could be a vacum leak somewhere?

[oldodge41]

How about your point gap and ignition timing? They can cause rpm related issues.

[Dozerman51]

Checked that too. The Dwell and timing are within specs.

[aero3113]

Check your plugs and wires in the dark with the engine running for arcing, one may have a crack in it causing a miss.

[greg g]

plug wires, small vacuum leak on one cylinder. Had a volvo once that ran great but had a miss at idle, after replacing all teh tune up parts, a small leak was discovered in the itake gasket for cylider number 4.

[Joe Flanagan]

I had a car once that had a leak at the intake manifold gasket. The symptoms were exactly what you describe. Ran rough at idle but was fine at speed. I discovered it by shooting carb cleaner around the mating surfaces of the manifold and block. Replaced the gasket and that did it.

[randroid]

Dozer,

Seems like you have everybody's attention on the first question so I'd like to address the second: Yes, you can port the block while it's in the car, and just as quickly watch the cast iron shavings you couldn't clean out get into the cylinders and bearings and oil galleys and destroy everything.

You definitely want to have the block out of the vehicle and stripped clean before the porting, and boiled out immediately afterward so there's no chance any of that stuff will find its way anywhere other than proper disposal, and there aren't many shortcuts I'd bet my engine on. Promise.

-Randy

[Dozerman51]

Thanks all,

Randroid, I won't be "Porting" anything except maybe some wine.LOL. Greg g and Aero3113, you may have hit upon something. I'll check the manifold by spraying some carb cleaner around it. I did notice a small dark spot on the side of the head gasket opposite #5 cylinder. Perhaps it's a leak. I am not getting any coolant in my oil though. You all have a nice Sunday.

Joe Giraud

[Dozerman51]

Thanks also to Joe F and Oldodge41 for all the help.