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| | | | Joined: Sep 2010 Posts: 1,712 back yard wrench turner | | back yard wrench turner Joined: Sep 2010 Posts: 1,712 | I just reinstalled my Zenith carb back on my truck after having it off for 3 years. It will not idle down. Runs really fast probable 2500 rpms. I did not try to rebuild it. I did adjust the float to 1 1/2 inches. Where do I start to get it to idle and run correctly? the motor is a '55 GMC 270, the carb is the factory one. carb tag
Last edited by Wayne67vert; 02/17/2026 9:09 PM. Reason: spelling
Wayne1938 1-Ton Farm TruckStovebolt Gallery Forums1989 Silverado 1996 Mustang GT convertible When I die, I hope she doesn't sell everything for what I told her I paid for it! | | | | | Joined: Oct 2021 Posts: 6,844 'Bolter | | 'Bolter Joined: Oct 2021 Posts: 6,844 | I assume that turning the mixture screw in and out has no effect? Ditto the throttle screw?
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)
| | | | | Joined: Jan 2022 Posts: 2,469 'Bolter | | 'Bolter Joined: Jan 2022 Posts: 2,469 | Disconnect choke, manual throttle and gas pedal throttle linkages.
Does it still idle really fast?
If no, fix your linkage problem(s).
If yes, can you manually pull the carb's throttle lever back to idle?
'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.
| | | | | Joined: Jan 2014 Posts: 3,689 'Bolter | | 'Bolter Joined: Jan 2014 Posts: 3,689 |
1951 3100
| | | | | Joined: Nov 2002 Posts: 2,766 Carburetion specialist | | Carburetion specialist Joined: Nov 2002 Posts: 2,766 | Either the answer given by Bill or the one by JW51 should find the issue.
Jon
Good carburetion is fuelish hot airThe most expensive carburetor is the wrong one you attempt to modify. If you truly believe "one size fits all," try walking a mile in your spouse's shoes!The Carburetor Shop | | | | | Joined: Aug 2010 Posts: 605 'Bolter | | 'Bolter Joined: Aug 2010 Posts: 605 | Does it have a PCV valve, and is it attached/working correctly?
1965 C60 school bus | 1967 GMC 6500 school bus
| | | | | Joined: Sep 2010 Posts: 1,712 back yard wrench turner | | back yard wrench turner Joined: Sep 2010 Posts: 1,712 | Thank you gentlemen!
It was a combination of 2 issues.
The gasket under the carb spacer was leaking and the linkage rod connecting to the carb was too long.
A new gasket, adjust the linkage rod and it runs awesome.
Wayne1938 1-Ton Farm TruckStovebolt Gallery Forums1989 Silverado 1996 Mustang GT convertible When I die, I hope she doesn't sell everything for what I told her I paid for it! | | | | | Joined: Jan 2014 Posts: 3,689 'Bolter | | 'Bolter Joined: Jan 2014 Posts: 3,689 | Vac leaks are sneaky. There have been times I’ve thought….”ain’t no way that gasket is leaking enough to matter”
….and been wrong.
1951 3100
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