ENGINE MISS

[BRUCESTUDE]

I HAVE IN MY SHOP A '51 COMMANDER THAT I REBUILT LAST YEAR, THEN AFTER THE OWNER GOT IT BACK, IT SAT!( I PUT ABOUT 50 MILES ON IT, CHANGED THE OIL, RETORQUED THE HEADS, ETC.) THE OWNER RECENTLY FIRED IT UP, IT RAN CRAPPY, SO HE DRAINED THE GAS PUT IN NEW GAS, AN IT STILL RAN LOUSY, SO HE BROUGHT IT OVER HERE. I CLEANED OUT THE FUEL FILTER, TORE DOWN AND CLEANED THE CARB, AND CHECKED THE TIMING, AND IGNITION SYSTEM. IT MISSES AT IDLE SOMEWHAT, NOT REGULAR THO. WHEN I REV IT UP AND HOLD IT AT MODERATE RPMS, IT WILL OCCASIONALLY POP THRU THE CARB, WANTS TO DIE OFF, THEN WHEN IT SLOWS DOWN IT REALLY MISSES AND DIES.
I'VE CLEANED THE PLUGS, CHANGED PLUG WIRES (NEWER SUPPRESSION TYPES REPL. W/USED COPPER SET)ETC. ETC. COMPRESSION IS 125-130 PER CYL.
I'M THINKING MY VALVE TAPPET SETTING HAVE CHANGED, POSS. ON A COUPLE CYLS.WHEN IT GETS WARM, OF COURSE THIS WOULD GET WORSE. BEFORE I PULL THE VALVE COVERS, DO YOU GUYS HAVE ANY OTHER IDEAS?[B)]

[Roscomacaw]

How about a failing coil or condensor? Even the cap, for that matter.

Miscreant at large.

1957 Transtar 1/2ton
1960 Larkvertible V8
1958 Provincial wagon
1953 Commander coupe
1957 President 2-dr
1955 President State
1951 Champion Biz cpe
1963 Daytona project FS

[hank63]

Came across a GM product with a similar challenge not long ago. EVENTUALLY diagnosed the cause - the coil bracket was loose thus earthing intermittently.
/H

[BRUCESTUDE]

I'LL DOUBLE CHECK THOSE ITEMS AGAIN. I DID A SIMPLE COIL TEST; I HELD THE COIL WIRE NEXT TO THE BLOCK, OPENED AND CLOSED THE PTS., GOT A GOOD SNAP. I ALSO REPLACED THE CONDENSER W/A KNOWN GOOD ONE. I'LL TEST THE COIL MORE THOROUGHLY, CHECK THE CAP, TOO.
THIS IS A WEIRD ONE, AS IT IT NOT A "REGULAR" MISS. I'LL KEEP AT IT...[B)]

[curt]

I do think a bad coil will can have seizures of being a good coil and then seize into the bad mode again, round and round.

[gordr]

Bruce,

I think you are on the right track when you speak of tappet clearance. Possibly one of the intake valves is set too tight, or maybe a valve guide is sticky, which could be a real possibility on a fresh rebuild which "just sat".

I doubt the coil is to blame. A weak coil would be more likely to cause ignition failure when the engine is pulling under load, IMHO.

Another possibility cold be a vacuum leak. Pop-back through the carb can be a symptom of a lean misfire.

I'd reset the tappets, and maybe add a can of top-end lubricant to the fuel.


Gord Richmond, within Weasel range of the Alberta Badlands