The Stovebolt Site Forums The Shop Area The HiPo Shop Another non-typical engine problem

Here a strange one (I think). Fresh dist., carb rebuilt, new plug wires, clear fuel in glass fuel bowl, plugs have been cleaned. Starts and runs great up to 75 mph, for about 10 miles. Develops a bad miss. Pull plugs and the outer ones at all four corners are black and sooty. The ones in the middle of both banks are a nice brown. Remember it's a 12 cylinder. What do you think guys, gals and Hotrod Lincoln ? Thanks

Uh?

gas tank isn't venting enough at higher speeds?

Is the miss from multi cylinders and random or can you find several cylinders dead continously?
Does the miss go away when the engine is cooled and restarted?
Are the missing cylinders fed from the same intake "runner"?
Does the miss remain at idle and does the spark remain strong and regular?
Sooty plugs can indicate rich mixture or misfiring cylinder.
What does manifold vacuum read when the misfire is occuring?

Thinking more about your "flathead-and-a-half", I wouldn't do anything before making sure I had a clean set of plugs in place to see if the problem lay there.
I never was around the v 12 much but my experience with the same tech v 8 ford made me believe that they were much less able to deal with plug fouling conditions than our chevy 6.The chevy would live long and work well with high oil consumption that would foul plugs regularly on the Ford flathead.
And now we have problems finding the right heat range plugs for the old flatheads (18MM) and our fuel likes to short a coated insulator more than usual--this adds up to my suggestion to look to the plugs first for this trouble.
Good luck and keep us posted please--we're learning too.

18MM plugs were only used on the early OHV V-8 engines- - - -mid-1950's 239, 272, 292,312, etc. Flatheads used 14MM plugs.

Black and sooty is too rich- - - -start looking for a vacuum leak near the center cylinders that is causing the power valve on the carburetor to open up and flood the corner cylinders, while compensating for a lean condition near the center. Use a Propane torch with a piece of rubber tubing on the snorkle instead of the flame nozzle, or an acetyline torch with a little fuel gas flowing (NOT LIT!) and run the gas around the intake-to-block gasket with the engine running at a fast idle. If you find a leak, the RPM will go up and the miss, if any, will smooth out. That long, skinny intake manifold can be warped near the middle. Draw-file it or mill it flat if necessary and be sure to torque the bolts when you install it. It's also possible to get an internal leak on that engine- - -from the crankcase to the intake, so run just a little gas into the oil filler tube. Don't overdo that one- - - -we don't want a crankcase explosion!
Jerry

Jerry, I think you're right that the 38 zephyr is 14MM--that is the year Ford downsized the v8 from 18MM in the old 21 stud flatheads.The 32 v8 was the only year using the 7/8-18 thread plug like the A model.
The first year y-block (1954) was the only year to use 14MM in it.

I seem to remember some engines using a 1/2" pipe thread on the plugs, with no gaskets. Maybe I'm thinking of some of the farm tractors from the 30's and 40's. I had a couple of the old take-apart plugs with the removable porcelain in a late-1940's Scott-Atwater outboard motor once, sort of like the ones used on T-Models.
Jerry

sounds like the chock is still on.