Holley Carb Problems

[landy]

I bought a '71 GMC 1500 with 350 engine and manual trans. Came with a Holley street performer 4 bbl w/vacuum secondaries and electric choke.

I can't get the idle speed down to below 1000 rpm or so and could use some suggestions. Here are the details:

Carb looks pretty new. Truck runs great. Starts easily when cold.

Adjusted the timing to factory specs. It was way off so that helped bring the idle down. Checked for vacuum leaks. Backed out the idle speed screw, disconnected the return spring, and made sure the throttle linkage was all the way forward. Backed out the fast idle speed screw all the way. Adjusted the idle mixture screws in and out, which made little difference on the idle speed and vacuum readings. Vacuum gauge is reading around 14 in at current idle speed.

Ah, the choke. When engine is completely warmed up, choke blade is not completely vertical as it should be. The choke linkage is set up such that it can't open completely. If a blade that's open all the way is 90 degrees from horizontal, this one opens a max of 65 to 75 degrees - maybe that's the way Holleys are set up? The bottom of the choke blade rod sits on top of the fast idle cam, so it can't open any further. I'm wondering if I need to bend the rod so that the choke can open all the way as I see no other means of adjustment. Exhaust does smell rich and maybe that's because the choke blade isn't open all the way.

Any thoughts?

[cableguy0]

Make sure the linkage isn't stuck on the fast idle cam. If the lowest idle you can get is 1k rpm the throttle linkage is stuck open or you have a serious vacuum leak somewhere. Manually disengage the fast idle cam. Open the throttle linkage slightly and push the fast idle linkage off of the primary linkage.

[landy]

Not sure how to manually disengage the fast idle cam. I opened the electric choke housing and there's a bolt that attaches the fast idle cam to the choke thermostat, so maybe I need to remove that complete assembly to do that?

[bob8619]

I'm new to carbs and have been learning a lot by watching their youtube videos. Have you checked them out?

[bob8619]

Oh and just push the fast idle cam to disengage it. At least on mine thats all you gotta do

[landy]

Yeah, I've looked through Youtube, and there's a lot of good info.

I don't think this fix is that simple. The fast cam is disengaged, but thanks for the suggestion!

[bob8619]

I wasn't saying it was the solution to your problem. You said you didn't know how to manually disengage the cam.

[cableguy0]

Ok next get yourself a can of carburetor cleaner. Spray around the intake and carb gaskets. If your idle changes you have a vacuum leak. Pinpoint the leak and replace the gaskets. Also disconnect everything that is hooked to the carb pulling vacuum. The brake booster,vac advance,pcv and everything else hooked up. Plug the ports at the carb if your idle suddenly drops when you plug the vac port at the carb you found a leak.

[landy]

I've done the carb cleaner spray around the base and vacuum fittings, but didn't pull the various vacuum lines. I'll try that.

Thanks.

[Captainfab]

If the choke flap is not fully open once the engine is warmed up, the choke is out of adjustment. Loosen the 3 screws that secure the choke housing and turn it counterclockwise until the choke flap is straight up.

[landy]

It's an electric choke. Rotating the choke cap has no effect on the position of the choke blade (i.e., it won't make the choke blade open any more), but controls how quickly the choke blade opens.

I should probably take a pic and post it, but I'll attempt to explain. When fully warmed up, the choke blade is open a max of 65-75 degrees. It physically can't open any further because the bottom of the rod that's attached to the choke blade rests on the top of the fast idle cam. The cam is forward as far as it can go, so the choke rod can't move any further. I'm thinking perhaps this is how the choke blade on this Holley carb is designed?

I've noted that the vacuum operated secondaries aren't opening when the throttle is opened all the way. I can manually open them and it kind of feels like there's binding at first opening. Perhaps as others have suggested, they aren't completely closed, which is causing an increased idle speed?

[GASoline71]

Unless there is a load on the engine... as in driving ... you will never see the secondaries open by opening the throttle while the vehicle is parked.

There is an off chance that someone messed with the secondary speed screw. Which opens the secondaries to let more air in at idle. Usually reserved for engine with a long duration camshaft.

How To Adjust The Secondary Speed Screw On Holley...

Gary

[landy]

Ah, of course, different vacuum conditions under load vs in park.

Thanks!

[storm9c1]

14" of vacuum at idle seems low for a stock or mild setup. Does this have a lopey cam or does it idle smooth?

Also factory timing specs are terrible (designed for emissions and 60s/70s fuel). A SBC likes 8-12 degrees initial at idle. Yes, this will bump up your idle speed. So once you solve the idle speed problem, I'd put the timing back in that range.

I agree that the next step is to disconnect all vacuum lines and plug them at the carb. Any difference?

I'm wondering about the choke setup too. Something doesn't sound right there either.

[landy]

AFAIk, the motor is original and stock. I think the idle vacuum reading will be lower as elevation increases. I'm a mile high above sea level, so 14 in. is probably ok.

[familyfast64]

Are you holding the throttle linkage open when turning the electric choke housing? That's how you have to do it in order to watch the choke blade move to 90

[familyfast64]

What carb do you have? I know you said street performer but I've only heard of the street avenger. I'm not trying to be a smart ass and correct you just making sure you don't have some old carb I've never heard of. Which is possible. If you do have the street avenger I can personally tell you mine doesn't work that way and someone prolly rebuilt it and didn't put it together right.

[familyfast64]

A stock motor should also have close to 20in hg. I don't think elevation has anything to do with vacuum bud. Just your air fuel ratio is all.

[familyfast64]

I would pull her off and rebuild it yourself so you know it's right. There's a few good videos and articles that will dumb everything down. You'll be thanking yourself later because tunning is a regular must do with carbs. Especially as weather changes. Once you learn all 4 circuits and how to diagnose issues with each you'll be balling. Lol

[landy]

FamilyFast64, you're wrong on the vacuum. A vacuum gauge reads the difference between a reference pressure (atmospheric) and a negative pressure (vacuum) inside your engine. Pressure varies with elevation, so the higher the elevation, the lower the reference pressure.

Here's a link that describes basic vacuum gauge theory. Refer to the note section under performing a vacuum gauge test.

http://www.gregsengine.com/using-a-vacuum-gauge.html

Anyway, back to the choke issue. I've looked at some Holley Carb youtube clips and they show the choke blade when fully opened as in the same position as mine, i.e., less than 90 degrees from horizontal. So I guess that must be the way Holley designed it.

Well, back to figuring out the idle issue.

[familyfast64]

Yup that makes sense. But still your only a thousand feet above sea level right? Would it effect it that much? And how do you know your spring in the choke isn't wound once two many times? Just adjust it to where it'll work. Then set your carb to the base starting point and tune.

[Captainfab]

The OP said he is a mile above sea level....that is 5280 feet which will affect his engine's vacuum considerably

Originally Posted by familyfast64

Yup that makes sense. But still your only a thousand feet above sea level right? Would it effect it that much? And how do you know your spring in the choke isn't wound once two many times? Just adjust it to where it'll work. Then set your carb to the base starting point and tune.

[landy]

FamilyFast 64, the electric choke works great, just as it should. Truck starts easily and runs good when cold, and good when fully warmed up. What I'm confused about, besides the idle issue, is that the choke linkage appears to be designed in such a way as to not allow the choke blade to open 90 degrees from the horizontal, i.e., more like 65 to 75 degrees. I guess if it runs good that way, I shouldn't sweat it and just focus on the high idle issue...

[familyfast64]

Ok but could you shave the blade? Sry for being wrong about the vacuums and ft above sea level. Thanks for clearing that up. I remember filing off the edges of the choke blade. would you be able to do something like this? Even if this doesn't effect your idle speed it should open to ninety correct? I was just trying to give a guy some help. Il opt out of this one.

[homemade87]

Landy, I have something like this happen before. Just put a little pressure on the choke blade to move it open and open the throttle a little and see if it opens all the way while holding pressuse on the blade. If it does realease the throttle while still holding pressuse on the choke blade and see if it stays open. If it does then the choke needs adjusting some how to correct. You could start it at this point but dont touch the gas peddle or it will go back.You could also do this while running. And check idle and see if it helps. The blade should always be at a 90* when fully warmed. This was from my experience. Hope this helps.