Hello all, awhile back my neighbor recruited me to help work on a 48 ton and a half with a late 50s 261. After giving it a tune up, carb swapping and fuel pump it starts and idles fine. Anything above 1/4 throttle and it starts missing whether or not it's under load almost like you flip a switch. We're both scratching our heads on it. Exhaust is unrestricted, can't find any vacuum leaks, and timing is set correctly. The vacuum advance port is capped at the carb because of a bad diaphragm. Any ideas on what to check? Thanks- Jordan
Either way it could be flooding. Stuck float, debris in needle and seat, etc.
1950 Chevrolet 3100 (Ol' Roy)
1939 Packard Standard Eight Coupe (The Phantom) | 1956 Cadillac Coupe de Ville (The Bismarck) | 1964 Ford Galaxie 500 coupe |1966 Ford Mustang (Little Red) | 1969 Pontiac GTO (The Dishpit) I 1979 Ford F-100 | 1976 Ford F-150 (Big Red) | 1995 Ford F-150 (Newt)
There is a difference between 261 Rochester carburetors and 235s, so if it is a carburetor issue, it's probably under powered. For a 1961 chevy 235, the main jet is .055. For a 1961 chevy 261 the main jet is .063. I put a 235 carburetor on mine to get it going, it worked ok, but accelerating off idle it would stumble and have a lean condition, would backfire. When I had it rebuilt the mechanic drilled the main jet out for me. Pic is from 1961 chevy truck shop manual supplement. yours is a bit older but should be the same idea.
Check the points to make sure they have enough spring tension. Some brands of points have a copper conductor strip, and a steel spring that can get misplaced. Without the steel spring, the engine will idle, but the points start bouncing and messing up the ignition timing at higher speeds. A bad condenser can also cause the same kind of problems, and they're notorious for being bad right out of the box. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
I'm with Jerry on this one. I saw it happen 7+ years ago and again recently on this forum. If you have a dwell meter you can watch the dwell get less and less as the RPM increases. It should stay constant.
Last edited by Bill Hanlon; 11/13/20225:48 PM. Reason: spelling
'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12 '52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.
