mustangsavage1967

Hi

I just bought this 600cfm holley carb 4160. Its for my ford 302. I had a 670cfm avengero n there before but managed to break the base plate...another story for another day. The old carb was ok and didnt have this problem. The car starts fine and the choke engages. When i disengage the choke the car drops down to 1000rpm and no matter how much i adjust the idle speed screw it doesnt change. I have never had this problem on a holley before so i dont know why now. I have looked and looked and cant find a solution. This is a brand new carb. any ideas? thanks

Please dont post in here and say buy another carb....Ive had holleys and edelbrock carbs..i like holley end of story

67mustang302

2 things to check quickly, 1 test for vacuum leaks. If it had no vac leak with the other carb then suspect the base plate gasket, or an unplugged open vacuum port on the carb. Spray brake cleaner around and see if the idle changes, if it does you found the leak. Second thing to check is the choke side of the carb, to make sure the fast idle speed screw from the choke isn't hanging up the fast idle cam and preventing the carb from idling down. I've had that happen a few times, usually from the high idle speed screw being set too high out of the box.

2+2GT

You must be the only person on the face of the Earth who has not had this problem with a Holley.

The gasket between the throttle body and metering plate is cross-bleeding.

67mustang302

You have absolutely no idea that's the case. And it's highly unlikely to be anything involving the metering system/blocks etc. High idles are usually large vacuum leaks or stuck throttles.

kalli

what exact carb is it? is it a vacuum secondary? or doubloe pumper. does it have four idle mixture screws or two?
i believe as well it could be as simple as a forgotten vacuum port. check this first.
if that doesn't get you anywhere and the carb is a doublepumper check for the idle speed screw on the secondaries. they might be open a bit too far. in some cases just a small allen key, check with manual

jspagna1

I'm with 67mustang302 on this one.

2+2GT

Did we get up on the snotty side of the bed this morning? I may be wrong, but I'm not condescending.

67mustang302

There's an expression that when you hear horse hoof beats, you look for horses and not Zebras.

I get tired of seeing people post "absolute" answers to problems that only have a 1/10,000 chance or less of actually being the problem. He doesn't need to go tearing his carb apart to replace gaskets when there's a 99% chance it's a vacuum leak or a stuck throttle. I've never seen a carb with a high idle problem that wasn't one of those 2...can it happen, sure, but highly unlikely.

And every time a Holley carb thread comes up people always want to talk about leaking gaskets, cross bleeding metering systems and blown power valves. Those basically never happen except in very rare circumstances, and I've never seen any of them. Can they happen, sure, but again it's highly unlikely.

When trying to troubleshoot a problem you always start with the simplest, most likely stuff first, especially over the net where you can't see/hear/feel/smell the problem. Once you know it's not the basic stuff THEN you go to the more uncommon reasons for a problem. But you don't start with stuff that's not likely to be the problem, and may even make things worse and introduce more problems. You just end up chasing your tail.

frdnut

As well as those checks check the secondary side to make sure the butterflies are not hanging up or have a linkage issue that prevents them from closing..They also should have an idle screw controlling how tightly they shut just like the primaries..You need to flip the carb over as I believe it goes in from underneath and can't be adjusted with the carb upright on the engine..

67mustang302

It depends on the setup, on some that use an Allen set screw, if the intake is tall enough you can fit a little Allen "L" wrench under it to set it....just barely. Of course, you have to have it off when you set it initially the first time to make sure you have enough transfer slot.