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?

[cool68]

go to holley.com and find tech info on your model carb. depending on what you have, adjust electric choke, turn down choke idle speed - small screw only seen at linkage set at full throttle (motor not running) below choke housing, don't just screw idle mixture screws in & out - need to follow procedure, seems that a return spring that runs from a bracket at front of motor to carb works best, reset primary idle screw, etc.

[kelbystanley]

Look on youtube for holley carb tech, They have some pretty good videos for tuning the carb. Mine is a 670 street avenger with the vacuum secondary. Truck idles @ 700 rpm in gear with brake and 900 in park.

[kelbystanley]

http://www.youtube.com/watch?v=5rpwL...ature=youtu.be

Here is a short video.

[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.

[geezer#99]

Have you closed the secondaries down a bit. If open too far they will keep your idle up.
Here's a link.

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

[landy]

cool68, I've done that, but wasn't ablt to get the idle speed down enough. I've looked on Youtube, but will look more.

Good tip on the secondaries, geezer. I'll check that.

Thanks for all the suggestions.

[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?

[geezer#99]

FWIW it's frowned upon to start 2 threads on the same subject in different sections.
You can have them merged. Pm a mod to merge them.

Also choke plates aren't always at 90 degrees. Some are intentionally askew to create flow or turbulance for the incoming air.

[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]

Thanks for the tip. I guess some websites are different. I'm a member of several other websites, which have various subboards, and all members don't read all subboards. So one may be able to get more help by posting on more than one subboards.

Regarding the choke blade, I was wondering if it being less than 90 degrees was the "factory" position. However, on other carbs that I'm familiar with, the choke blade is vertical in the fully open position. I thought I'd seen pics of this model carb with the choke blade completely vertical, but I'll keep looking.

Thanks.

[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.

[geezer#99]

Usually one way to tell if your choke is completely off is check to see if the secondaries will open. There's usually a lock out that's on if the choke is on.
Exactly what carb do you have?

[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]

As I noted in my original post, it's a Holley Street Avenger, although I mistakenly called it a performer. I don't recall the model no., but it's either a 570 cfm or 670 cfm model.

I'll check the secondary suggestion.

Thanks.

[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.

[geezer#99]

A quick way to make sure your choke is opening completely is loosen the 3 screws on the choke cap and rotate the cap all the way to the lean side. Then see where the choke blade sits.

[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 you suggested, they aren't completely closed, which is causing an increased idle speed?

[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?

[Aussie Ol' Blue]

I had a similar problem, turns out that there was a rubber grommet or plug on the carby that was cracked and letting in air. Once replaced it revved at it's proper range.

[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!