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Difficult to come off of high idle

stevolwevol

Well-known member
Joined
May 28, 2015
Messages
250
Location
Michigan
Corvette
1977 light blue
I've been driving in cooler than normal weather, but It seems like I am having trouble with the carb staying in high idle mode. It is idling high as I approach operating temp, then it finally lets off, but later than it should.

I located the screw that adjusts the cam tension if that's what it's called, and backed it out about 1 turn, but it still seems to stick in high idle too long. Input would be very helpful.
 

douglasamariani

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Joined
May 12, 2008
Messages
189
Location
Anaheim Hills CA.
Corvette
2008 6.2 Coupe,1980 L48 Coupe,1968 427/4spd Coupe
Have you checked the choke linkage? Check if it sticking? Is the choke butterfly opening all the way?
 

stevolwevol

Well-known member
Joined
May 28, 2015
Messages
250
Location
Michigan
Corvette
1977 light blue
Have you checked the choke linkage? Check if it sticking? Is the choke butterfly opening all the way?
Yes the butterfly opens, and closes when choke is engaged. I backed the screw another half turn beneath the choke linkage, and it went off high idle with ease this morning, but it was not as cold out either.
 

LLC5

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Joined
Sep 28, 2004
Messages
2,299
Location
Wa.
Corvette
98 black 6spd convert.
If you backed off the fast idle screw 1.5 turns that is a lot and your fast idle will be much lower. Does the choke housing have a plastic cover on it with 3 screws holding it in place? If so you can adjust the spring tension to open sooner in warmer weather. We used to have to adjust choke pull off’s seasonally also. PITA. Long live FI. 🙂
 

stevolwevol

Well-known member
Joined
May 28, 2015
Messages
250
Location
Michigan
Corvette
1977 light blue
If you backed off the fast idle screw 1.5 turns that is a lot and your fast idle will be much lower. Does the choke housing have a plastic cover on it with 3 screws holding it in place? If so you can adjust the spring tension to open sooner in warmer weather. We used to have to adjust choke pull off’s seasonally also. PITA. Long live FI. 
Ok, I have the three screw adjustment. I think if I turn it clockwise, the choke will be less, meaning the butterfly will be more open than if I turn it clockwise and the chock will close more. Is this also controlling the fast idle tension? What say you?
 

LLC5

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Joined
Sep 28, 2004
Messages
2,299
Location
Wa.
Corvette
98 black 6spd convert.
The choke cover is only a spring that controls how fast the choke plate will open and how hard it will shut when cold. The looser the spring tension the quicker the choke blade will open and the fast idle cam will drop to it's lower settings, and eventually has no idle speed control when fully open. Make sure you mark the original cover setting and loosen it 1/4-1/2" or 1-2 marks if it has them and try that. Don't go too far too fast, just a little at a time and retest. It can take a lot of patience like in the not so good ole days. This adjustment should only be done if the engine and carb are working properly.
 

stevolwevol

Well-known member
Joined
May 28, 2015
Messages
250
Location
Michigan
Corvette
1977 light blue
LLCS, I'll move it a little tonight. It will be cool in the morning, and the engine will be bone cold. The carb is working very well, and all the linkage as far as I can tell is working. Also when the fast idle is engaged, the secondaries won't kick in. I noticed this myself. Backing off the screw was needed because I thought the engine was racing too much for a cold engine. I'll post my results. Thanks...
 

LLC5

Well-known member
Joined
Sep 28, 2004
Messages
2,299
Location
Wa.
Corvette
98 black 6spd convert.
After setting the choke when cold, usually two pumps of the throttle, high fast idle should be about 2000 rpm or so (check spec's for your vehicle) and when the choke pull off is open and you tap the throttle again it should drop to around 1200 rpms on the fast idle cam second step. These speeds are approximations as every vehicle and engine combination can be different.
 

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