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| | | | Joined: Jul 2004 Posts: 19 Apprentice | | Apprentice Joined: Jul 2004 Posts: 19 | I have a 72 K20 with a 350, q jet carb. The truck cold starts fine but the choke will open all the way as soon as it starts, making warmup a little difficult. Is the tension on the bi-metallic spring on the intake supposed to override the vaccume cylendar to give me half choke and high idle during warmup? The spirng is not broken but seems week.
1971 GMC 5500(gone but will never forget), 1972 K20 with plow
| | | | | Joined: Nov 2005 Posts: 6,100 'Bolter | | 'Bolter Joined: Nov 2005 Posts: 6,100 | Hy 71bigbolt, Yes the choke should come off slowly, the choke pulloff should not fully open the choke immediately after starting a cold engine. Check how much the choke is set when the engine is cold, just open the throttle once when the engine is cold, and the choke should set itself, it should not be closed really tightly, but it should cover most of the airhorn, it can be adjusted by straightening/bending the rod that connects the thermostatic spring to the carb, hope that helps. | | | | | Joined: Nov 2006 Posts: 2,544 Shop Shark | | Shop Shark Joined: Nov 2006 Posts: 2,544 | When the truck is cold before starting, open the throttle so the choke sets. It should close against the airhorn and when you tap on it you should hear a slight snap as it closes back against the airhorn. Then take the vacuum pull-off hose off and push the choke pull-off in (back towards the chamber). This will show you how much the pull-off is opening the choke. The amount it opens the choke plate should be just enough to get a 5/16" drill bit into. The other adjustment to check is the fast idle speed. This screw is on the passenger side of the carb and down underneath the choke arm. Once the truck warms up you should be able to tap the throttle and then the idle screw on the drivers side can be adjusted for the idle speed. Good Luck Don | | | | | Joined: Jul 2004 Posts: 19 Apprentice | | Apprentice Joined: Jul 2004 Posts: 19 | ok thanks,Ill tinker with it today.I will post later.
1971 GMC 5500(gone but will never forget), 1972 K20 with plow
| | | | | Joined: Jul 2004 Posts: 19 Apprentice | | Apprentice Joined: Jul 2004 Posts: 19 | checked it this morning,the vaccume pull off is keeping the choke wide open as soon as vaccume comes up. even with holding the choke partially closed its fighting to keep it open.(this is after startup without touching throttle after start).
1971 GMC 5500(gone but will never forget), 1972 K20 with plow
| | | | | Joined: Nov 2006 Posts: 2,544 Shop Shark | | Shop Shark Joined: Nov 2006 Posts: 2,544 | If you look at the link that the choke pull off pulls against to open the choke you will see a big U in it. If you spread the U apart it will shorten the amount it opens the choke plate. If you take the vacuum hose off the pull off and move it by hand you will be able to tell how much its opening the plate. This should get you close without having to start the truck. Once you get the pull off adjusted then you can move on to other adjustments. Good Luck Don | | |
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