fast idle adjustment question
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fast idle adjustment question
I have a 69 427 tri power (holley carb) and have a question about the fast idle adjustment at start up. When I start the car when cold I press the accelerator once to the floor which sets the choke. The car usually turns over pretty easily but it only idles at 600 rpms or so. Isn't there a fast idle setting that should kick in and cause it to idle at around 1500 rpms? Is there somewhere to adjust that.
Thanks
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to test and verify your choke, begin with cold motor off,
trip the throttle lingage and the choke should pull to the closed position,
use a heat gun on the thermo-stactic metal can,
to simulate the motor warming up, you should see the choke arm move to the hot position,
let it cool back down, and verify it goes back to the cold position.
if all that works adjust your cold idle screw, to the rpm you desire.
trip the throttle lingage and the choke should pull to the closed position,
use a heat gun on the thermo-stactic metal can,
to simulate the motor warming up, you should see the choke arm move to the hot position,
let it cool back down, and verify it goes back to the cold position.
if all that works adjust your cold idle screw, to the rpm you desire.
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The curb idle and [cold] fast idle are both set warm, when the car is completely up to normal operating temperature.
When setting fast idle with engine running, open throttle a bit manually and move the fast idle cam to where the second step (next to highest) of the cam is aligned with the fast idle adjustment screw...then release the throttle so that the screw rides on that second step. Now, adjust that screw until the rpms reach the fast idle specification. You can also 'burp' the throttle to drop out the cam and then set the curb idle to its specification (usually around 1200 rpm).
When the engine is cold, the fast idle cam will be engaged and the engine will be running at an elevated rpm setting. It will not be near the specification rpm (since that was set when warm); but it will allow the engine to be running smoothly during a cold start (700-900 rpm).
When setting fast idle with engine running, open throttle a bit manually and move the fast idle cam to where the second step (next to highest) of the cam is aligned with the fast idle adjustment screw...then release the throttle so that the screw rides on that second step. Now, adjust that screw until the rpms reach the fast idle specification. You can also 'burp' the throttle to drop out the cam and then set the curb idle to its specification (usually around 1200 rpm).
When the engine is cold, the fast idle cam will be engaged and the engine will be running at an elevated rpm setting. It will not be near the specification rpm (since that was set when warm); but it will allow the engine to be running smoothly during a cold start (700-900 rpm).
Last edited by 7T1vette; Aug 11, 2016 at 09:43 AM.
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From: At my Bar drinking and wrenching in Lafayette Colorado
The Holley Tripower (and many of the OEM-installed Holley 4-barrels) does not have a fast idle adjustment screw. It uses a slotted tang that rides on the fast idle cam, seen here:
To increase fast idle, simply stick a screwdriver in the slot and twist the tang to bent it slightly towards the cam. It usually takes a few tries to get the speed just right - I usually set the cold idle speed on a cold running engine to about 1300 - 1350.
Lars
(Photo courtesy "Tom454" from C1/C2 Forum)
To increase fast idle, simply stick a screwdriver in the slot and twist the tang to bent it slightly towards the cam. It usually takes a few tries to get the speed just right - I usually set the cold idle speed on a cold running engine to about 1300 - 1350.
Lars
(Photo courtesy "Tom454" from C1/C2 Forum)
Last edited by lars; Aug 13, 2016 at 12:03 PM.
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The Holley Tripower (and many of the OEM-installed Holley 4-barrels) does not have a fast idle adjustment screw. It uses a slotted tang that rides on the fast idle cam, seen here:
To increase fast idle, simply stick a screwdriver in the slot and twist the tang to bent it slightly towards the cam. It usually takes a few tries to get the speed just right - I usually set the cold idle speed on a cold running engine to about 1300 - 1350.
Lars
(Photo courtesy "Tom454" from C1/C2 Forum)
To increase fast idle, simply stick a screwdriver in the slot and twist the tang to bent it slightly towards the cam. It usually takes a few tries to get the speed just right - I usually set the cold idle speed on a cold running engine to about 1300 - 1350.
Lars
(Photo courtesy "Tom454" from C1/C2 Forum)
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From: At my Bar drinking and wrenching in Lafayette Colorado
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From: At my Bar drinking and wrenching in Lafayette Colorado
Yes, it is bolted directly to the throttle shaft. By resting on the fast idle cam, it cracks the throttle open until the fast idle cam drops down out of the way. The tang is the lever (the only lever) bolted to the throttle shaft with a phillips screw - it has the slotted hole in it for a screwdriver blade - I showed it clearly in the photo I posted above, and it's visible in 2 of your photos. Stick a screwdriver in the slot and twist it to bend the lever either towards the fast idle cam or away from the cam to change the fast idle as desired.
Lars
Lars
Last edited by lars; Aug 21, 2016 at 05:14 PM.
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Yes, it is bolted directly to the throttle shaft. By resting on the fast idle cam, it cracks the throttle open until the fast idle cam drops down out of the way. The tang is the lever (the only lever) bolted to the throttle shaft with a phillips screw - it has the slotted hole in it for a screwdriver blade - I showed it clearly in the photo I posted above, and it's visible in 2 of your photos. Stick a screwdriver in the slot and twist it to bend the lever either towards the fast idle cam or away from the cam to change the fast idle as desired.
Lars
Lars
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From: At my Bar drinking and wrenching in Lafayette Colorado
Last edited by lars; Aug 21, 2016 at 07:42 PM.
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Yeah. I just went and looked again. It's all there. Right now the choke is open as I just ran the car and the engine has not cooled yet. I saw the slot to insert a flat blade screw driver. When twisting clockwise it will cause the cam to stop on different steps. I'm not sure the choke is setting when I push the accelerator pedal to the floor. Should the butterfly valve close when setting the choke? How do I make sure the choke is setting properly?
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From: At my Bar drinking and wrenching in Lafayette Colorado
When the engine is dead cold, the choke should snap closed, and the plastic fast idle cam should rotate, when the throttle is cracked open. This is a simple function of the bi-metallic spring on your intake manifold pushing upwards on the rod and lever. If it pushes upwards, it will close the choke and set the fast idle cam into position.
The throttle spring position is certainly interesting... It's obvious that the center carb has had a return-to-idle problem, so someone has re-positioned the spring to pull forward at the top of the lever rather than pulling back from the bottom of the lever. This will often solve a problem with the throttle lever not returning consistently to the same idle speed. It's effective, but not correct. I would put the spring in its correct position and fix whatever is causing a return-to-idle problem.
Lars
The throttle spring position is certainly interesting... It's obvious that the center carb has had a return-to-idle problem, so someone has re-positioned the spring to pull forward at the top of the lever rather than pulling back from the bottom of the lever. This will often solve a problem with the throttle lever not returning consistently to the same idle speed. It's effective, but not correct. I would put the spring in its correct position and fix whatever is causing a return-to-idle problem.
Lars