High Idle speed after fixing accel pump on Holley carb. Looking for ideas while I think this through.

[will e]

I thought I was so smart. My car normally starts with one pump of the gas. When it didn't and I noticed an off idle stumble while in park (I didn't drive it) I knew it was the accel pump. I look down the carb and it was confirmed. Replaced the accel pump and now I have a high idle speed. I checked fuel levels, made sure the throttle wasn't stuck open, like a linkage issue. The choke doesn't work but I verified it isn't binding either. Adjusting the idle speed screw (not the mixture screws) had no impact in either directions. It was hot and I was tired of sweating so I shut it down and went home to think about it.

Plan of action:
Verify I didn't create a vacuum leak. The most likely culprit would be the pcv. I know I hooked it up to the carb but perhaps it came off at the valve cover, mine is hidden in the passenger rear by the engine bay struts. . I will also check that I didn't mess up a vacuum plug. The number of vacuum connections I use on the carb is very limited. Just the pcv and the outboard carbs, which isn't manifold or ported.
Next i will take a peak down the carb throats to confirm the butterflies are all closed.
Then I will spray around the carbs with some water but this isn't a small leak, it's idling as high or higher than a fast idle setting on a working choke. So I doubt this will 'find a leak'
Finally I will test the timing. I use manifold vacuum for the distributor off of a manifold port. I will unplug it just to see. And I did have to remove a spark plug wire at the cap to get the front carb off, I didn't feel the distributor move but anything is possible.

For a moment I thought perhaps it is the power valve but that causes a rich condition, it wouldn't cause fast idle. Same if any of the fuel bowls were overflowing. The only reasons I can think of that will cause a fast idle is 'more air', from a leak or the throttle open or from an advanced ignition. As I mentioned, it didn't get any faster (or slower) speed from turning the idle speed adjustment. Yeah, I am leaning towards a big vacuum leak. Which would be nice.

Any input from the gang?

 

[Sheriff41]

Check that your fast idle cam on the choke side isn't hung up.

 

[Bill Kanode]

I thought I was so smart. My car normally starts with one pump of the gas. When it didn't and I noticed an off idle stumble while in park (I didn't drive it) I knew it was the accel pump. I look down the carb and it was confirmed. Replaced the accel pump and now I have a high idle speed. I checked fuel levels, made sure the throttle wasn't stuck open, like a linkage issue. The choke doesn't work but I verified it isn't binding either. Adjusting the idle speed screw (not the mixture screws) had no impact in either directions. It was hot and I was tired of sweating so I shut it down and went home to think about it.

Plan of action:
Verify I didn't create a vacuum leak. The most likely culprit would be the pcv. I know I hooked it up to the carb but perhaps it came off at the valve cover, mine is hidden in the passenger rear by the engine bay struts. . I will also check that I didn't mess up a vacuum plug. The number of vacuum connections I use on the carb is very limited. Just the pcv and the outboard carbs, which isn't manifold or ported.
Next i will take a peak down the carb throats to confirm the butterflies are all closed.
Then I will spray around the carbs with some water but this isn't a small leak, it's idling as high or higher than a fast idle setting on a working choke. So I doubt this will 'find a leak'
Finally I will test the timing. I use manifold vacuum for the distributor off of a manifold port. I will unplug it just to see. And I did have to remove a spark plug wire at the cap to get the front carb off, I didn't feel the distributor move but anything is possible.

For a moment I thought perhaps it is the power valve but that causes a rich condition, it wouldn't cause fast idle. Same if any of the fuel bowls were overflowing. The only reasons I can think of that will cause a fast idle is 'more air', from a leak or the throttle open or from an advanced ignition. As I mentioned, it didn't get any faster (or slower) speed from turning the idle speed adjustment. Yeah, I am leaning towards a big vacuum leak. Which would be nice.

Any input from the gang?

Put a vacuum gage in place to confirm that you do have a vacuum leak.

 

[Zach]

If the idle screw does little to nothing you more than likely have a leak that is UNDER the throttle blades, air has to be getting to the engine somehow in order to raise rpm. Maybe a bad seal to the manifold, make sure the bolts are only hand tight, and verify you didn't crush AND have the gasket in the orientation, ask me how I know. An easy way to check for a leak is to place your hand over the primaries to cut air flow to the carb normally, if the idle doesn't die out or even change it is a vacuum leak, but like I said if the throttle blades don't do anything the leak is under them.

In terms of readjusting the holley here are some tips in my few rebuilds.

Power valve would be a separate issue. If you have touched the curb idle screw at all I would verify that the transfer slot is squared off. Incase you don't know what that is or what I am talking about it is the long rectangular slot that is in the primary bores and under/being hidden by the throttle blade, unfortunately the carburator has to come off in order to flip it upside down and dial it in but it is worth it. You just want to screw the curb idle screw until the butterflies only show a tiny perfect square of the transfer slot when shut. If you turn the curb idle screw too much it'll open that transfer slot too much or not enough which can cause a bog. Once you have it squared it is best if you never mess with the curb idle screw specifically.

In terms of holleys they are all pretty similar just want to be careful cause they are fragile. To dial in your floats you want to make sure the carb is full of fuel, turn on electric pump or crank the engine a bit, open the sight plugs (if they aren't the glass kind), proper level is when gas spills out if you give the car a shake or two, if you have a 4 barrel there are two sight plugs total. If they aren't at a good level you need a flathead and a wrench and fiddle with the bolt on top of the float bowls. Be gentle cause you will wreck the gasket, ask me how I know. Also if you have an electric fuel pump you need to make sure you are not above around 7 psi of fuel pressure I believe. Also be careful with the fuel inlet they strip out easy, ask me how I know.

Fuel mixture screws can safely be turned all the way in to seat gently then I think its 3 full turns out as a good base line if they are messed up at all, turn in either direction to get highest/most stable rpm.

This was just a quick write up with some tips to find the issue, if you need something more specific I can elaborate more.

 

[rcadd1ct]

Did you remove the carb to fix it?

If so make sure gasket isn’t hanging the blades open or you didn’t warp the base not tightening the bolts in a crisscross pattern

 

[Randyi00]

I had the exact same issue a couple months ago after I removed the carb for the purpose of changing the carb spacer. Long story short, I discovered a VERY SMALL tear in the carb gasket that was creating a vacuum leak. Replaced the gasket and problem solved. It doesn't take much to create a vacuum leak and throw the idle out of wack that's for sure.

 

[mrgmhale]

I have a video on a 2100 2v carburetor where I show how to adjust the high speed idle screw for when the chole is (parially) on. You may need to adjust it, or check to make sure it is able to drop freely when the chick is warmed up and upen. I am not sure what carb you are running, but on a lot of carbs it is pretty challenging to find and adjust the high speed idle screw.

I hope the video helps:

https://www.youtube.com/watch?v=mwLwwUtI1cE

 

[will e]

Still working on it.
More clues:
When I remove the hose PCV from the carb base there is little to no change in the idle speed, even if I use my finger to plug and unplug the port
When I remove the brake booster hose from the manifold port there is a noticeable change.
When I was checking the choke cam I moved the throttle open/closed to see if it was 'hanging', it isn't HOWEVER a small amount of fuel escaped from the throttle shaft. It was getting wet from the accel pump shooting fuel into the carb and appears to have leaked out a bit.
It diesels when i turn it off. This indicates the additional air is getting mixed with fuel so it's probably being drawn in from the carb itself (or the base seal).

It's a 50 year old carb, I don't know all of the history on it, but I am leaning towards the shaft leaking. It's always idled a bit high and on occasion it has dieseled. Perhaps pulling it off and farting around with it made it even worse.

I am going to pull it to verify the butterflies are closed as it sits and to recheck the gasket.

I might swap it to another car just to see how it idles on something different, this will confirm if it is the carb.