Stuck on fast idle?
08-10-2018, 03:32 PM
#1
Pro
Thread Starter
Stuck on fast idle?
My stock '75 L48 stick with Quadrajet seems to be sticking on the fast idle when I start it, racing to around 2500 rpm, after a minute can get it down if I hit the gas. if I try hitting the gas at before that it keeps racing.
Once warm idling and running fine.
I replaced both choke pull offs and the choke thermo, is there a procedure to adjust for the fast idle from the choke pull offs?
Once warm idling and running fine.
I replaced both choke pull offs and the choke thermo, is there a procedure to adjust for the fast idle from the choke pull offs?
08-10-2018, 03:50 PM
#2
I found this procedure to set up your choke and fast idle
2. Integral Choke Systems (1975-1981)
Remove the three screws holding the black choke cover to the choke housing and remove the cover. If rivets are used, drill out the rivets.
Crack the throttle slightly open and push up on the choke coil lever inside the choke housing until the choke is closed.
Notice that there is a small 1/8” hole recess inside the choke housing which will appear right below the lower edge of the choke coil lever when you push the lever up. Insert a 1/8” drill bit in this recess and allow the lever to rest on the drill bit.
In this position, your choke blade should be fully closed. If not, bend the choke intermediate rod that comes up through the body of the carb and attaches to the choke blade lever. Bend the rod so that the choke blade is fully closed.
Now, remove the drill bit, crack the throttle slightly and rotate the fast idle cam (the steel counterweight that rotates on the choke housing shaft between the choke housing and the carb body) so that the fast idle cam follower is positioned on the second step of the cam, right up against the edge of the highest step.
In this position, apply light finger pressure on the choke coil lever inside the choke housing to close the choke (lift up on the lever).
The choke should be cracked open 5/16” as measured between the rear upper edge of the choke blade and the rear airhorn wall. Use a drill bit to check this.
To adjust, notice that there is a small sheet metal tang attached to the lower side of the fast idle cam. This tang determines the travel range of the choke. Bend the tang to adjust.
Now, install the choke housing cover to the choke housing. If you’re using an electric choke, DO NOT use a gasket between the cover and the housing. Be sure that the choke coil tang in the cover correctly mates with and engages to the choke coil lever inside the housing.
With the cover attach screws loose, rotate the cover so that the indicator scribe line points straight up. This should fully close the choke. If there is no scribe line (electric chokes do not have lines), rotate the cover counter clockwise until the choke blade is fully closed. Lightly snug the cover attach screws to keep the cover in this position. You may need to crack the throttle open to get the choke to snap closed.
Remove the short piece of vacuum hose attaching the choke pulloff to the vacuum nipple on the carb. Attach a long (about 2’) vacuum hose to the pulloff.
Suck on the vacuum hose to retract the choke pulloff. If the pulloff does not retract, it must be replaced.
With the pulloff fully retracted, use your other hand to lightly push down on the forward lower edge of the choke blade to simulate to force of the air across the blade. This will open the choke slightly. At this point, measure the distance between the forward lower edge of the choke blade and the forward wall of the airhorn. This distance should be ¼”. You can use a ¼” drill bit as a simple gauge to check it. To adjust, turn the screw on the end of the choke pulloff lever. After each adjustment, you must release the vacuum on the hose and suck on it again to re-seat the pulloff, each time apply the light finger pressure to the forward lower edge of the choke blade.
Once completed, loosen the choke coil cover attach screws and rotate the cover clockwise. On hot air choke systems, the cover scribe mark should be aligned with the second dot clockwise of the center dot on the choke housing marks. On electric chokes, the indentation in the outer edge of the cover should be aligned with the screw & clip location towards the forward side of the choke housing. Snug the screws down or re-install new rivets. (NOTE: On riveted applications, the rivet holes can be tapped for #10 screws.)
Re-attach the vacuum hose to the pulloff and the carb.
This completes choke adjustment for an integral choke carb.
2. Integral Choke Systems (1975-1981)
Remove the three screws holding the black choke cover to the choke housing and remove the cover. If rivets are used, drill out the rivets.
Crack the throttle slightly open and push up on the choke coil lever inside the choke housing until the choke is closed.
Notice that there is a small 1/8” hole recess inside the choke housing which will appear right below the lower edge of the choke coil lever when you push the lever up. Insert a 1/8” drill bit in this recess and allow the lever to rest on the drill bit.
In this position, your choke blade should be fully closed. If not, bend the choke intermediate rod that comes up through the body of the carb and attaches to the choke blade lever. Bend the rod so that the choke blade is fully closed.
Now, remove the drill bit, crack the throttle slightly and rotate the fast idle cam (the steel counterweight that rotates on the choke housing shaft between the choke housing and the carb body) so that the fast idle cam follower is positioned on the second step of the cam, right up against the edge of the highest step.
In this position, apply light finger pressure on the choke coil lever inside the choke housing to close the choke (lift up on the lever).
The choke should be cracked open 5/16” as measured between the rear upper edge of the choke blade and the rear airhorn wall. Use a drill bit to check this.
To adjust, notice that there is a small sheet metal tang attached to the lower side of the fast idle cam. This tang determines the travel range of the choke. Bend the tang to adjust.
Now, install the choke housing cover to the choke housing. If you’re using an electric choke, DO NOT use a gasket between the cover and the housing. Be sure that the choke coil tang in the cover correctly mates with and engages to the choke coil lever inside the housing.
With the cover attach screws loose, rotate the cover so that the indicator scribe line points straight up. This should fully close the choke. If there is no scribe line (electric chokes do not have lines), rotate the cover counter clockwise until the choke blade is fully closed. Lightly snug the cover attach screws to keep the cover in this position. You may need to crack the throttle open to get the choke to snap closed.
Remove the short piece of vacuum hose attaching the choke pulloff to the vacuum nipple on the carb. Attach a long (about 2’) vacuum hose to the pulloff.
Suck on the vacuum hose to retract the choke pulloff. If the pulloff does not retract, it must be replaced.
With the pulloff fully retracted, use your other hand to lightly push down on the forward lower edge of the choke blade to simulate to force of the air across the blade. This will open the choke slightly. At this point, measure the distance between the forward lower edge of the choke blade and the forward wall of the airhorn. This distance should be ¼”. You can use a ¼” drill bit as a simple gauge to check it. To adjust, turn the screw on the end of the choke pulloff lever. After each adjustment, you must release the vacuum on the hose and suck on it again to re-seat the pulloff, each time apply the light finger pressure to the forward lower edge of the choke blade.
Once completed, loosen the choke coil cover attach screws and rotate the cover clockwise. On hot air choke systems, the cover scribe mark should be aligned with the second dot clockwise of the center dot on the choke housing marks. On electric chokes, the indentation in the outer edge of the cover should be aligned with the screw & clip location towards the forward side of the choke housing. Snug the screws down or re-install new rivets. (NOTE: On riveted applications, the rivet holes can be tapped for #10 screws.)
Re-attach the vacuum hose to the pulloff and the carb.
This completes choke adjustment for an integral choke carb.
08-10-2018, 04:32 PM
#3
Pro
Thread Starter
Thanks, great procedure.
Any guidance on the screw on the front choke pulloff ? I think this is the issue, I adjusted choke thermo without issue. I replaced both choke pull offs, but just the front pull off that has the screw and spring alone, left it as it came out of the box.
Any guidance on the screw on the front choke pulloff ? I think this is the issue, I adjusted choke thermo without issue. I replaced both choke pull offs, but just the front pull off that has the screw and spring alone, left it as it came out of the box.