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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: Chevhughes on March 04, 2016, 09:27:43 am
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Hey there, I don't know my carb info off by hand as of right now, but I have a high idle question. The truck is from California and has every piece of smog equipment on it and in working order. The truck runs perfectly, starts perfectly.. my only complaint is on the cold start. On a cold start, reguardless of the outside air temperature the truck will idle for 4-5 minutes before kickdown. I have never owned a chevy like this, any I've had will kickdown rather soon.. Is there a easy way to adjust this without playing with choke etc, because like I said the truck starts, runs perfectly. Thank you in advance for your help.
Cliff Hughes
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Four to five minutes is a long time - should be closer to three minutes depending on ambient temperature. Make sure that 14 volts (engine running) is actually reaching the choke thermostat terminal and that the choke housing is properly grounded. Inspect and verify that the choke vacuum breaks are working. Make sure that the choke fast idle cam on the passenger side of the carburetor rotates freely with the throttle open and not hanging up - wash the choke cam and linkage with B12 or similar carb spray and check whether the green Teflon coating on the shaft that protrudes from the back of the choke housing is beginning to peel. If the Teflon peels loose it can cause binding of the choke fast idle cam and delay the cam's rotation and return to curb idle. All of the above can be performed without altering any adjustments. What is the cold idle RPM?
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use some spray lube on the choke linkages probably just dry and accumulating rust , if that doesnt work slightly loosen the three screws on the choke adjustment ( keep your thumb on the center disk its spring loaded ) and give it a turn 1 or 2 notches towards lean should be arrows on the disc . try in that order also the fast idle screw if over adjusted will cause it to bond a bit you can loosen it off half a turn.
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If it's a Cali truck then the carb is an electronic q-jet with Computer Command Control?
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Four to five minutes is a long time - should be closer to three minutes depending on ambient temperature. Make sure that 14 volts (engine running) is actually reaching the choke thermostat terminal and that the choke housing is properly grounded. Inspect and verify that the choke vacuum breaks are working. Make sure that the choke fast idle cam on the passenger side of the carburetor rotates freely with the throttle open and not hanging up - wash the choke cam and linkage with B12 or similar carb spray and check whether the green Teflon coating on the shaft that protrudes from the back of the choke housing is beginning to peel. If the Teflon peels loose it can cause binding of the choke fast idle cam and delay the cam's rotation and return to curb idle. All of the above can be performed without altering any adjustments. What is the cold idle RPM?
How do you check voltage to the choke coil when the engine is running? Just red to the metal tang connector on the choke and black to ground using voltmeter?
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How do you check voltage to the choke coil when the engine is running? Just red to the metal tang connector on the choke and black to ground using voltmeter?
Correct
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How do you check voltage to the choke coil when the engine is running? Just red to the metal tang connector on the choke and black to ground using voltmeter?
Correct
Ok, so the service manual says (i have a different choke issue which is why i had to look in the manual) says that if the volts are between 12-15 and it takes longer than 5 mins for the choke to open then you need a new choke. If you're getting 0 volts then something is wrong with the wiring---or could be the oil pressure switch. But Cliff, the OP says that it runs ok when warm which makes me think he just needs a new choke?
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Stewart, is there a question? If a poor electrical connection resulted in 8 volts across the choke t-stat, or 5 volts, or 10 volts - in other words, less than system voltage, what do you suppose would happen? For the sake of simplicity, the service manual merely posits the extremes of a range of possibilities.
IMHO, if the voltage drop across the choke t-stat equals system voltage, there is no problem with the choke stat in the OP's particular circumstances. Choke thermostats fail for various reasons, however few, but it is rare.
If you wish to pursue this further, you should start a new thread.
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Chevhughes, I take this is a new truck to you?
It's not a problem that just started?
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I have had the truck for 2 years and it has been like this since I have owned it .. At first I thought maybe for the smog in Cali this was normal, but the more I think about it other gm vechiles i have owned basically kickdown when you are ready to pull out.. I will check, lube linkage in the next day or so. The truck is completely rustfree and I do not drive it in the winter. It lives in PA now and spring is right around the corner
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Linkage could be hanging up, dirty.
Runs fine otherwise so choke pull-off is ok.
Should kick down from high step to the next step on fast idle cam right after start by touching pedal slightly.
If not the linkage is misadjusted or dirty.
2-3 minutes for the electric choke to completely open. you can start cold and time the choke flap till its completely open. Any longer than that the choke coil is bad or not getting 12 volts. Should not have a gasket under the choke coil.
85 model could have two pull-offs, front or rear or both depending on carb.
Spray your linkages with carb cleaner for the choke.
Don't move the throttle too much with engine off or you will flood the engine with the accelerator pump.
Search for choke quadrajet, lots of info out there with pics.
If you can book store it and get cliff ruggles Quadrajet book. Has a web sit also.