I just bought a new Holley carb (P/N 0-80457s) it is a 600 vacuum secondary with electric choke. I am putting it on a 65 mustang with a 289. The old Autolite 4100 worked fine except for back barrels. This new Holley will not idle at all and runs very rough at low RPM. At high RPM it smooths out but jumps around about 500rpms. If you touch the gas at all it jumps up 3000rpms stays there for awhile and then comes back down and dies. I can adjust out the touchiness but can not make it run right below 3000 or idle AT ALL. Please Help.

Sounds like a vacuum leak or a misadjusted idle mixture, have a look at the idle mixture needles to make sure they aren't grooved from being seated to hard. Many other factors can cause your problem, look for obvious ones before you blame the carb. This carb is a universal type so expect to have to change the jetting etc., to suit your engine.

Whats the timing set at? Is the problem hot or cold? Does it get better when hot?

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The problem never gets any better whether it is hot or cold. Nothing else was touched doing the carb install and the old carb ran PERFECT. It seems to me like a vacuum leak somewhere but the only vacuum lines are the one to the ignition advance, pcv, and the choke tubes. however someone put a carb spacer with a pcv port that I closed off but maybe not good enough. As far as the misture goes it seems to run better almost completly closed off (LEAN). New timing chain and distribuotr cap, coil, rotor, wires, and plugs. timing should still be 10. I even disconected the advance no difference at all. Also not sure if the fuel bowl level is right seems low to me but I would think it should idle just not run right on the top end.

Spray around the base of the carb and where you blocked off the PCV with carb cleaner. If it smooths out, you've found your leak.

I agree with the vacuum leak scenario and always use the spray technique.It's possible that the leak sould have caused the 4100 secondaries not to work depending where it's at. Those 4100's are virtually trouble free so that raises some questions to begin with.

If you are using the stock factory 289 intake I know of one version that had a base pad that allowed a full manifold vacuum leak at the rear of the carb where it overhangs the base pad. A solid spacer solved the problem, although the Autolite carb and the Holley share bore spacing there can be a leak because of the shape of the base plate.

Check it out.

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Outlawed tunes from outlawed pipes

The intake (65 factory 4V) already has a 1 inch spacer on it already. The old gasket on the bottom was missing a corner but I installed a new one. It will not run long enough for to check for a vacuum leak. Even with a vacuum leak would the car not at least idle and run rough. It will not stay running at all with out half throttle. The base plate bolts were tq correctly. My understanding is that these should be bolt on and ready to go. The front bowl adjustment was sent to me so tight it had split the gasket and leaking fuel. Thinking about taking it back and going with an edelbrock. I have rebuilt one of these and run it on my truck with out any problems. I will see what happens when I get home but so far not to impressed with Holley they will not even answer my email.

[ April 25, 2003: Message edited by: tonylsg ]</p>

last time I had a problem like that it was a vacuum line I forgot to cap. Can you say 'major vacuum leak'?
I would also try and peek down the carb throat while someone helps you keep her running and see if she's dumping gas.

I could not figure out and neither could any one else locally. I could never see that it was dumping gas at idle but nick the throttle and it went full bore. No vacuum leaks. After no responses from Holley I took it back in favor of an edelbrock. It took all of 15 minutes to hook up, set mixture, and idle. Runs absolutely perfect. It will be edelbrock from here on out for me. Thanks for the help HOTRODDERS.

Tony

Don't get excited about an Edelbrock carb. I've got the same problem. The idle screws do even work.

I have one on sb chevy and have no problems out of it. Let it sit for a month and she still fires right up. I did rebuild about 6 months ago and it only took about an hour. Put it back on and it fired right up again. Everyone has a preferance, and I may have just gotten the bad one of the bunch. However poor tech support on Holley's part was the deciding factor. I personally have no complaints with edelbrock and until then I will stay excited

The sec. is hanging open....

A real simple test to do if you run into a situation like this is when the engine is running is to press on the accelerator pump arms without moving the throttle linkage. This adds more fuel without changing the amount of air the engine sees. If the engine smooths out it's too lean, and wants more fuel. If it runs worse it's already too rich, and wants less fuel.