mdtoren

Hi!

Just did a Carb swap on my 86 tpi, I put a Holley street avenger 570cfm on an edelbrock mani with an inch spacer. I can't get the car to idle down much past 1500 rpm. The curb idle screw is all the way out, fuel pressure at 5 psi, and it revs fine. On start up it runs around 2k until I assume the choke kicks down and itll drop to about 1500 after that if I tap the gas.

I emailed Holley and they said it was a vac leak and to get the carb cleaner and start hunting..did that and sprayed it all over the carb mounting surfaces, manifold, and spacer surfaces with no change in rpms at all. If I pull the brake boostervac hose idle shoots way up making me question if it's vacuum..

A final note in the event it helps..the engine sometimes diesels when I shut it down but I believe that's caused by not shutting the fuel pump down long enough before turning the engine off.

sofakingdom

iTrader: (1)

You have a vacuum leak. Pure & simple.

Check every fitting on the carb and everywhere else. Verify that you used the right base gasket.

mdtoren

By base Gasket I assume you mean to the carb? I used all of the gaskets that came with the carb/spacer. When bolting the manifold down I noticed there was play in the gasket until I completed the torque sequence then it was gone, I sprayed a lot of Carb cleaner there and nothing changed. I practically soaked the carb and nothing. I hate vacuum!!!

sofakingdom

iTrader: (1)

Yeah, vacuum SUCKS... so does gravity

Gotta find the leeeeeek though.

DonW

Are you sure he doesn't just need to adjust the fast idle screw that is located behind the electric choke housing...the one where you have to press the throttle lever all the way forward to access it? That will make it idle really fast too. My new carb was idling fast like that till I found that screw and whipped it into shape with a 1/4 open ended wrench!

DonW

Your carb should have came with instructions on that fast idle adjustment. Its a pain in the neck to see and to get to, but trust me IT IS THERE and can be turned down to lower your idle. Of all people, I learned this from Sofa while doing a google search before I even joined this forum lol.
Basically, while leaning into your engine bay from the passenger side, you will see the secondary diaphragm and the electric choke housing side by side. Reach over the carb and SLOWLY push your throttle lever to WOT while looking between the secondary diaphragm housing and the electric choke housing. That 1/4 screw will reveal itself. Screw it in to speed up idle, or turn it out to slow it down. From what I have read they almost always come with the idle set too fast. Mine did. That fixed it.

LG4TA

If that does not work. Pull the carb off and flip it over. Make sure the throttle blades are shutting all the way. If the secondaries are open there should be a tiny screw under the base plate that can be adjusted to open or close them slightly. Close them if they are open.

mdtoren

So I adjusted to fast idle screw and got the idle tondrop to about 1500 in park, 1000 in gear. I read that I might need a Carb sealing plate to seal the Holley carb to the edelbrock manifold and that might be cause for a vac leak. I sprayed Carb cleaner again and noticed a slight drop (100 rpm or so) around the base of Carb now that it is idle down enough to hear it. Anyone experienced with these sealing plates?

WickedBowtie

skinny z

At one time I was using a gasket assembly that consisted of two carb base gaskets and a steel spacer which wasn't much more than 1/16th thick. (I needed that bit of room for clearance). Problem was, the sealing surface between the separate components was very narrow and it would leak. I eliminated the clearance issue, got rid of the plate and the problem.
Why do you have a 1" spacer?

mdtoren

I got the 1" spacer because I'm a moron and didn't read that the 4150 style Carb would get the throttle plates stuck on the 2101 intake manifold openings...I couldn't get the carb to wot so the 1" spacer gives me the room I need to drop the throttle plates down all the way and get to wot

DonW

If it were me, I would HATE to pull the carb back off because I HATE spilling fuel all over the intake as we all do, but I definately would go ahead and pull it in your case just to double check that you have the right gasket on there and to check it for tears from over-tightening etc... Also, while you have it off, LG4TA mentioned above to check your secondary transition slots. Thats a good idea too, and just part of tuning a Holley. With the carb off, flip it over. The transition slot should only be exposed very little. There is a small screwon the bottom-side of the base-plate to adjust the secondary throttle blades. You want them closed to the point that the transition slot looks "square" and not rectangular. That should put you around .030 to .050 of transition slot exposure which is what you want. Once you get that adjusted and have the right gasket with a good seal go back to your fast-idle screw located behind the electric choke housing and keep turning it down until you get the idle you want. Pain in the culo i know, but..

EDIT: If it hasn't already been advised, I like the Holley tuning sticky at the top of the carb forum. Follow it step by step and you should come out with a great running carb!

mdtoren

A resolution to this - After all this, I contacted Holley, went round and round through their trouble shooting and finally, exchanged it for a new carb under warranty. I got it, looked it over, got pissed because it looked the same, sent another mad email to Holley about it asking for more help and thats when I got an out of office reply....so...I thought screw it, Ill try it, and installed it, primed it, and it fired up with full idle control and idles perfectly ever since. Guess it was something with that carb? Rare but it happens, sometimes its just faulty and who knows where the fault was.

skinny z

Well, it's good to hear you got to the bottom of it. Also nice that Holley did step up with their warranty. Sometimes it doesn't work out that way.
Thanks for the follow up. Sometimes guys reach out for advice but there's no feedback. Even if the suggestions didn't necessarily contribute to the cure.