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73-87 Chevy _ GMC Trucks => 73-87 Chevy & GMC Trucks => Topic started by: Steve341 on July 16, 2013, 05:09:02 pm
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1975 Chevy c20 454 automatic. Trying to set the fast idle on my truck as it runs like complete junk until the truck warms up and choke starts to let off. I can turn the fast idle adjustment screw all the way in or almost all the way out and there is no change in the idle. There is a rather large spring loaded screw that operates the fast idle right above the adjustment screw if I turn that it kicks up. This is on the passenger side of the carburetor. Am I doing something wrong on the fast idle adjustment? Is there another screw ? It's a real pain to have to sit in the cab with my foot on the gas waiting for the choke coil to unwind and open up the choke. I might add the coil is mounted on the intake manifold and not on the carb itself. I'm guessing divorced choke?
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Yes I was doing this with a cold engine.
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4MV divorced choke Quadrajet:
Flip to page 6M-19 (page 461), Figure 2C of the 1974 Service Manual (http://www.73-87chevytrucks.com/techinfo/7387CKMans//Service/ST_330_74_1974_Chevrolet_Light_Truck_Service_Manual.pdf) for the choke fast idle adjustment procedure.
1975 ushered in the M4MC Quadrajet carburetor that used a "married choke" thermostat, so your vehicle was built just prior to the production change (or the carburetor & manifold were swapped following manufacture).
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Do you have an electric coil? If so adjust it to the weather it should only have enough tension to close
Sent from my SGH-T769 using Tapatalk 2
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no electric choke, hot air
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Still the same adjustment :-)
Sent from my SGH-T769 using Tapatalk 2
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I repaired the throttle lever so I am not going to worry about fast idle. When I pull it out it will idle up. Push it in, it will idle normal. It gently pushes on the gas pedal when its pulled out.