Carb Question
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Joined: Feb 2001
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From: San Luis Obispo, CA
Carb Question
I have a model 1904 Edelbrock Q-jet. The fast idle cam sticks so that you have to manually push it down atfter the engine is warmed up. Any tips on how to correct this?. Bought the Carb new over a year ago but finally just got it installed and running on the crate motor. Thanks :flag
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Joined: Aug 1999
Posts: 14,366
Likes: 6,348
From: At my Bar drinking and wrenching in Lafayette Colorado
Re: Carb Question (Clay78)
The fast idle cam simply rotates as a slip fit on the shaft between the choke housing and the carb. If it's sticking, either something is bent or there's some crud in it. To fix, you need to pull the entire choke housing off the carb and examine the linkage for the problem. Clean it, straighten it, dry it well and pop it back together. When you pull the housing off, you will loose the choke link hooked up to the choke housing inside the carb - if you haven't done this operation before, let me know, and I can run you some steps to get through it.
Tech Contributor
Joined: Aug 1999
Posts: 14,366
Likes: 6,348
From: At my Bar drinking and wrenching in Lafayette Colorado
Re: Carb Question (Clay78)
Clay -
First, of course, verify that the problem is, in fact, with the fast idle linkage:
With the engine fully warmed up so that the choke is off, shut the engine down. Open the throttle slightly. You can jam a screwdriver into the linkage on the driver's side to hold the throttle a little ways open.
With the throttle jammed open, the choke counter-weight and fast idle cam assembly on the passenger side should rotate completely freely on the shaft between the choke housing and the carb. You should be able to lift the cam weight assembly up, let go, and it should drop freely and smoothly all the way down to the hard-stop. Do it several times to verify that it either is, or is not, operating freely. Observe the interaction of the fast idle screw (located down low under the choke housing) with the fast idle cam as you move the linkage with your finger. Identify, if possible, where the bind-up is occurring.
If you really do have something binding, you will most likely need to pull the choke housing with the choke linkage off the carb to repair it. It is not uncommon for things to get bent and sticky, or for a piece of crud to get into the pivot point of the counter balance and make it stick. If you need to pull the linkage off, it's often easiest to yank the carb off the engine and to do these operations on the comfort of a workbench.
Remove the choke rod from the choke plate lever. Some late carbs have a screw in the lever attaching it to the choke. Remove the screw and lever. Earlier carbs have a simple clip attaching the rod to the choke plate lever. Remove the clip and disengage the rod from the lever.
The rod will stay engaged to the choke coil lever inside the carb, down low on the passenger side. Leave it engaged for now.
If your choke pull-off diaphragm is attached to the side of the carb with two screws, remove the screws, and remove the diaphragm with the secondary airvalve rod. If your choke pulloff diaphragm is pressed into a bracket that is not attached with two screws, leave it in place.
Remove the 3 screws that attach the round black choke cover to the choke housing and remove the cover. Remove the single screw in the middle of the inside of the choke housing and hold onto the choke housing. Notice the installed configuration of the secondary lockout lever located on the secondary throttle shaft on the passenger side. This lever will likely fall off during the next operation, so notice where it goes and how it's installed. With one hand, hold the choke plate rod that is sticking up out of the top of the carb. With the other hand, pull the choke housing assembly with the levers straight off the carb. Once the housing clears the carb, you can pull the choke rod straight up and out of the carb with the little lever arm dangling from it.
With all the parts off the carb, you can correct whatever area is binding up and make it work smoothly.
To re-install the choke housing, dangle the little choke lever arm from the choke rod and carefully drop it down into the carb. Look in the hole in the side of the carb that the choke housing engages with lever arm and lower the arm until the hole in the arm is visible through the carb hole. Hold it right there. Now, engage the choke housing assembly with the carb by slipping the choke housing shaft into contact with the dangling lever arm on the inside. Once contact is made, you can drop the lever arm down. This will rotate the arm, and it will engage with the flat sides of the choke housing shaft. Once it engages, you can finish fully engaging the choke housing to the carb body and re-install the single screw in the center. Before you install the screw, make sure the secondary lockout lever has been correctly installed. If it is not, you can pull the choke housing far enough away from the carb to allow installation of the lockout lever without disengaging from the choke lever inside the carb.
Piece of cake. If you need real-time assistance, I can call you on the phonewhile you're doing it and talk you through it. No problem. You're gonna' be a Q-Jet expert in no time...!
First, of course, verify that the problem is, in fact, with the fast idle linkage:
With the engine fully warmed up so that the choke is off, shut the engine down. Open the throttle slightly. You can jam a screwdriver into the linkage on the driver's side to hold the throttle a little ways open.
With the throttle jammed open, the choke counter-weight and fast idle cam assembly on the passenger side should rotate completely freely on the shaft between the choke housing and the carb. You should be able to lift the cam weight assembly up, let go, and it should drop freely and smoothly all the way down to the hard-stop. Do it several times to verify that it either is, or is not, operating freely. Observe the interaction of the fast idle screw (located down low under the choke housing) with the fast idle cam as you move the linkage with your finger. Identify, if possible, where the bind-up is occurring.
If you really do have something binding, you will most likely need to pull the choke housing with the choke linkage off the carb to repair it. It is not uncommon for things to get bent and sticky, or for a piece of crud to get into the pivot point of the counter balance and make it stick. If you need to pull the linkage off, it's often easiest to yank the carb off the engine and to do these operations on the comfort of a workbench.
Remove the choke rod from the choke plate lever. Some late carbs have a screw in the lever attaching it to the choke. Remove the screw and lever. Earlier carbs have a simple clip attaching the rod to the choke plate lever. Remove the clip and disengage the rod from the lever.
The rod will stay engaged to the choke coil lever inside the carb, down low on the passenger side. Leave it engaged for now.
If your choke pull-off diaphragm is attached to the side of the carb with two screws, remove the screws, and remove the diaphragm with the secondary airvalve rod. If your choke pulloff diaphragm is pressed into a bracket that is not attached with two screws, leave it in place.
Remove the 3 screws that attach the round black choke cover to the choke housing and remove the cover. Remove the single screw in the middle of the inside of the choke housing and hold onto the choke housing. Notice the installed configuration of the secondary lockout lever located on the secondary throttle shaft on the passenger side. This lever will likely fall off during the next operation, so notice where it goes and how it's installed. With one hand, hold the choke plate rod that is sticking up out of the top of the carb. With the other hand, pull the choke housing assembly with the levers straight off the carb. Once the housing clears the carb, you can pull the choke rod straight up and out of the carb with the little lever arm dangling from it.
With all the parts off the carb, you can correct whatever area is binding up and make it work smoothly.
To re-install the choke housing, dangle the little choke lever arm from the choke rod and carefully drop it down into the carb. Look in the hole in the side of the carb that the choke housing engages with lever arm and lower the arm until the hole in the arm is visible through the carb hole. Hold it right there. Now, engage the choke housing assembly with the carb by slipping the choke housing shaft into contact with the dangling lever arm on the inside. Once contact is made, you can drop the lever arm down. This will rotate the arm, and it will engage with the flat sides of the choke housing shaft. Once it engages, you can finish fully engaging the choke housing to the carb body and re-install the single screw in the center. Before you install the screw, make sure the secondary lockout lever has been correctly installed. If it is not, you can pull the choke housing far enough away from the carb to allow installation of the lockout lever without disengaging from the choke lever inside the carb.
Piece of cake. If you need real-time assistance, I can call you on the phonewhile you're doing it and talk you through it. No problem. You're gonna' be a Q-Jet expert in no time...!
