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Dead Parrot · 12-06-2018, 01:09 PM

Quick check for choke. Should be closed on first cold start. Should start to open within a few minutes. Needs to wind up fully open when engine hot.

A lot of times, they wind up being set rich, meaning they don't open all the way or open later then the engine needs as it warms up.

If all the choke linkages are working, when the choke is open enough, the secondary throttle plates will work. Until then, they are locked shut. Don't confuse the throttle plates with the top plates(forget the proper name). The top plates open by air pressure as the lower throttle plates open. The top plates via a small hanger, pull up the secondary rods and allow more fuel to flow to the secondary holes.

Early Q-jets had a metal stove mounted on the passenger side of intake. PITA to adjust. Later versions had a heat tube that ran from the intake to the control unit on the passenger side of the carb. Even later versions replaced the heat tube with an electric heater. Both of the later versions can be adjusted by rotating the black cover. (May have to drill out rivets and replace with screws, several threads on topic).

Check your timing. A lot of idle problems are really timing related.

If yours has electric choke, make sure the wire(IIRC some version of green) is connected and has power with the engine running. IIRC - a lot of these also run to the oil sender so the choke heater doesn't pull juice when the motor is off.

2nd the call for some good picts.

12-06-2018, 01:09 PM	#10
Dead Parrot Registered User Join Date: Aug 2012 Location: Oklahoma City, OK Posts: 2,479	Re: 81 GMC K35 454 Carbwork/New Selection? Quick check for choke. Should be closed on first cold start. Should start to open within a few minutes. Needs to wind up fully open when engine hot. A lot of times, they wind up being set rich, meaning they don't open all the way or open later then the engine needs as it warms up. If all the choke linkages are working, when the choke is open enough, the secondary throttle plates will work. Until then, they are locked shut. Don't confuse the throttle plates with the top plates(forget the proper name). The top plates open by air pressure as the lower throttle plates open. The top plates via a small hanger, pull up the secondary rods and allow more fuel to flow to the secondary holes. Early Q-jets had a metal stove mounted on the passenger side of intake. PITA to adjust. Later versions had a heat tube that ran from the intake to the control unit on the passenger side of the carb. Even later versions replaced the heat tube with an electric heater. Both of the later versions can be adjusted by rotating the black cover. (May have to drill out rivets and replace with screws, several threads on topic). Check your timing. A lot of idle problems are really timing related. If yours has electric choke, make sure the wire(IIRC some version of green) is connected and has power with the engine running. IIRC - a lot of these also run to the oil sender so the choke heater doesn't pull juice when the motor is off. 2nd the call for some good picts.