The Stovebolt Site Forums The Shop Area Engine Shop 4 Barrel Holley Carb Question

I bought a 4 barrel 600cfm carb off of Ebay awhile back. I gave it a rebuild kit (I've rebuilt a few without any problems) but this one is acting funny. The truck fires up right away, but instead of going down to idle, it keeps reving up! After revving really high the motor dies. I have a few theories.

1. The floats need to be adjusted
2. The secondaries are stuck open on the carb gasket
3. I really screwed up the idle adjustment screw

Anyone have any experience with this?

That carb has vac secondarys. Adjusting the float is not hard, a little low to start would be better than high, once it's idleling fine you can readjust the float.
I'd start with idle screws turned out 1 1/2 turns, that should let it run at least.
Why it wants to race kinda says it's getting gas from somewhere until it uses it up and shuts down.
I think I'd pull it off and re check what I did to make sure things are the way they are supposed to be. At least a holley is simple to tear down.
Dan

Gas cannot make the idle speed up, only air.

When the choke is partially closed, the engine gets more fuel/less air and the engine idle speed goes up.

Builder;

It's kinda both. When the choke is closed it opens the throttle plates via linkage to give a fast/high idle. Regardless I can't figure out why the engine would start, rev high and then die. It's almost like it has both an air and fuel problem. Hope to see the solution on this thread.

SimS

Vac leak I would check to see if You have any vac leaks it's common that if theres a vac leak the engine will use the gas thats in the manifold than will not get gas from the carb because of a lack of soction from the engine thru the carb so You get the high RPMs than nothing


Pete

Ok, well, I guess I'll try the floats and the Idle screw first. I really do not want to go through and rebuild the carb again if I can help it. I'll check for vacuum leaks too, but that will be hard if I only have a few seconds to check it while its running. Wow, it could be a lot of things. Getting down to the bottom of this may prove difficult.

I'm not sure I understand this quote:
"Vac leak I would check to see if You have any vac leaks it's common that if theres a vac leak the engine will use the gas thats in the manifold than will not get gas from the carb because of a lack of soction from the engine thru the carb so You get the high RPMs than nothing"

You say there is gas in the manifold, why would there be gas in the manifold upon start-up, besides maybe one pull from the carb? My truck will run for about 10-15 seconds, even if there was gas in there to start it wouldn't last 10-15 seconds.---

When You pump the carb to set the choke the acc. pump dumps some gas into the manifold but here isn't suction because of a vac leak she will not keep running.I had this happen on a SB the engine backfired and took out a small section of the intake gaskit.

Pete

Problem solved. Turns out it was just the carb gasket was covering up a few ports on the bottom of the carb. I took a razor blad and cut the gasket on the inside and problem solved.