New Holley wont idle

[jhuethk20]

Hey everyone, new to the whole forum thing but since Im rebuilding a k20 I thought it would be a good idea,

So my problem today is, that I just got a new Holley 600 Carb for my 350.
It was running fine when I had a Qjet that I rebuilt was installed. Then today after installing the Holley it wont run unless I keep the rpms at 2000, and dies out as soon as you take your foot off the gas. Im sure everything is plugged in right and doesn't appear to have any vacuum leaks. Also have tried adjusting the idle screws in and out and it doesn't seem to make a difference.

Thank you I advance for any insight.

[Fairlane514]

Sounds like a vacuum leak.  You should be able to start out with your curb idle adjusted with .020 transfer slot.  You will have to remove the carb and turn it over to see the transfer slots in the primary butterflies. If you have to adjust it a whole lot form there, you have a problem.

Where are your idle mixture screws set?

[gildardo01]

2x i also think its a vacuum leak....

[454Man]

X2 on the idle screws. Sounds like they are not backed our far enough. If the throttle has to b open that much it means the idle circuits sent functioning properly. Also could B A big vac leak. small ones usually make the engine idle high not shut off at idle.

[jhuethk20]

I started with the screws backed out 1 3/4 and went to 3.
I got it running and idling yesterday for a while but then I noticed secondaries dripping steadily,  so I adjusted their float level and then it won't idle again unless the curb idle  is up to 2000rpms. Another question is, Holley says 7.5 fuel pressure would flood the Carb. As far as I can tell because I have a mechanical fuel pump with cheap gauge that bounces from 5 to 10, so could it be flooding and bogging out?

Thanks for the replies

[Fairlane514]

If it was flooding you would have a lot of black smoke going out of the tailpipes. Its also possible you have a bad power valve, which would also flood with fuel causing black smoke.

You should have to run it at 3 turns out with your mixture screws, normally around 1-2. Make sure all unused ports on the carb are plugged, and check the plugs to make sure they are not cracked. Another source for a vacuum leak can be the brake booster. Just behind the master cylinder is a rubber seal which can crack and of the years and become a source for a leak. You will have to remove the master cylinder to check. You can probably just unbolt the master and pull it away without disconnecting the brake lines.

Use a small propane bottle like for a torch, and attach a length of rubber hose (about 1 1/2 feet) and with the motor running guide the hose around the base of the carburetor and intake manifold where all the gasket surfaces are and see if the motor picks up rpm. Of course DO NOT light the propane, you just a want a small steady flow of propane that with ignite when it is sucked (vacuum leak) into the fuel system. 

[jhuethk20]

Thanks Fairlane, good suggestions, I decided to rebuild the Carb since the Guy I bought it from painted it with cheap paint and the gas was peeling it off, the only thing that seemed to be wrong was rear float was stuck up, but after I put it back together it ran and idled good. So its a mystery why it. Wouldn't run in the first place.

[Fairlane514]

Incorrect float levels can cause all sorts of problems.