So when I first start my '72 Supreme after sitting for a while, it loads up and idles rich at around 400-500 rpms for a couple minutes until it smooths out and settles in at around 750 rpm. I always set the electric choke with the throttle before I hit the key, and have even tried different scenarios (one pump, then feathering until it starts, one pump then just the key...etc). I have the two rear jets leaned out, but could the front two jets need tweaked? It's been about 3 years since I set the carb, and other than minor idle adjustments, I haven't done anything else.

For reference, it's a Holley 770 Street Avenger with an Edelbrock Performer intake, HEI feeding a 455 with a .030 bore and W30 cam with Hooker headers.

 

400 to 500 rpm on startup it way too low. Should be 950 to 1100 rpm

 

Agreed on the cold idle speed, it should be on the fast idle cam at that point (assuming the Avenger has a fast idle setting). The secondaries shouldn’t have anything to do with idle speed. Get the choke and fast idle set correctly.

 

Chokes should be opened a crack when you start the engine, if they are not, that could be causing your problem.

 

I'll double check that tomorrow...also, if I just leave it alone and don't mess with it, any long term effects other than using more fuel at startup?

 

Yes, washed cylinder walls and thinned out gas diluted oil.
It's not Rocket science to get the choke and fast idle set correctly.

 

In addition you get fouled plugs, carboned up valves, and exhaust system.

 

I tried to adjust the choke tonight, but couldn't get the choke cap to turn..any ideas?

 

Loosen screws more.

 

The choke cover is nothing more than that - a metal cover. As suggested loosen the screws completely - you can also remove them. It may be necessary to take a very tiny screwdriver & place it between the edge of the choke cover plate and the choke body and with a little twisting motion lift (free up) the cover plate ever so slightly as sometimes the cover plate will adhere to the choke body from slight gunk, corrosion from metal to metal.

 

Another possibility is either weak needle/seat or too high fuel pressure which when you start floods the engine a little bit. When it burns off and during steady state it runs fine. This could happen even with a warm engine that has sat 30 minutes or so.

 

I don't think it is a choke adjustment issue, rather it is a choke pull off problem. QJ's and most other carburetors have an external vacuum diaphragm to crack open the chock slightly shortly after the engine starts. I looked at the Holley web site and could not find an external choke pull off for your carburetor. I did find a choke fresh air port that is supposed to be left unplugged. Maybe you can check that for a restriction. If you don't find anything there perhaps the Holley tech line can help.

 

Thanks...I'll take a look.

 

Does the choke have 12 volts to ground w/engine idling?
Agree with Eric & Norm and others. Move the cover to its extreme clock & counterclockwise directions. You should see the choke butterfly move open n closed. Might have to actuate the throttle to get it to move.
Check the thermal choke spring behind the black cover for wear and for proper installation/direction The spring fits into the slot connected to the shaft of the choke butterfly.
There's also a tube that fits between the metal housing and carb float bowl. That should be intact with its gasket.

Do some Googling for visuals and get some literature on rebuilding and tuning Rochester carbs

 

 

TX Ralph, I was in QJ mode. But similar procedures should apply to any electric choke.

We are starting to chase our tails here. Let's regroup:

OP your choke is set to rich and RPMs are too low. I recommend 750RPM curb idle, 850 with AC. Also 10-12* base timing at 750/850 with A/F dialed in.
Verify 12 VDC is present at choke, engine running.
Find out what the Holley static spec is for the butterfly gap when cold. 1/8" gap is a good place to start. Does it have a vacuum choke pull-off? If so is it working?
Back choke off a little at a time. 1/32" of an inch increments towards the lean direction.

No carb will come out of the box ready to go. If you are lucky it will start and run good enough to dial it in, (timing and Air/Fuel mixture).
Tools required are a vacuum gauge, timing light, distributor wrench, and screwdrivers.

Holley does have a tech & chat line. You may find installation and setup instructions on the site as well.

Jets/rods/springs have absolutely NOTHING to do with the choke circuit. Please. reinstall the factory rods & jets!
Rods/jets/springs come into play from "off idle" to "WOT"...(wide open throttle). Rod/jets/springs are how you tune the engines road manners. That is another conversation.

You should make no other changes to the carb until you get the initial choke, idle and A/F set correctly. Only then should you start playing with rods/jets/springs. That conversation we can have, but do all of above first. Then we can address drivability concerns.

TX
Steve

 

Driveability is good...no issues there. I just need to adjust the choke...I know this because when I was trying to adjust it last night, I opened the throttle and the flap went fully closed..no gap whatsoever.

 

Dave - I watched this guy (from Holley) the other night. I found it the simplest and most straightforward presentation of any of the videos I watched. He explains it sweet & simple.

 

Yup Norm, that's the same video I watched too...notice how easily he is able to turn the choke cap?...no such luck for me. He barely loosens the screws and away he goes. Me on the other hand loosened them up to the point of almost coming out and the cap wouldn't budge.

 

It's because the cap, carb, and gasket are stuck to each other.

 

x2 Exactly. I suggested to Dave to use a tiny screwdriver. Not sure if he tried it. It “has” to come loose or you can remove the entire nine yards and replace it. Your choice, Dave.

 

Loosen the screws about two turns or so then tap on the cap with a screw driver handle. That should break the cap loose from the gasket and allow you to adjust it.

 

That is a properly functioning choke. Do not attempt to adjust it!
Ok. A lot of people are trying to offer helpful advice but if I understood your original question I think we are going the wrong way.
To clairfy;
The Holly Street Advenger was installed three years ago and the engine was starting and running good. Now your complaint is the engine always start ok but recently after the engine starts "it loads up and idles rich at around 400-500 rpms for a few minutes until it smooths out and settles in at around 750 rpm". This is not a choke adjustment issue. A properly working choke closes completely with a cold engine and opens completely as the engine warms up. The choke is controlled by a thermostatic coil. The coil tension when cold completely closes the choke plate. As the thermostatic coil heats up the tension slowly un-winds and the choke completely opens. You are not describing hard starting when cold. You have stated the choke opens fully as the engine warms up and the engine runs fine. Your choke is functioning exactly as it should. Attempting to adjust the thermostatic choke coil tension will either not close the choke (loosen the tension) or cause it not to fully open (increase the tension). Once again if I understand your complaint of rich running immediately after the engine starts that would be caused by the choke pull off. That overly rich mixture is also causing the incorrect (too low) fast idle speed. The engine can't run at the previously correct fast idle speed because of the overly rich mixture. Fix the choke pull off issue and the fast idle speed will come back to where it was for the last three years.
The choke pull off uses engine vacuum created by the just started/running engine to crack the choke blade open approximately a 1/4 inch or so (specs vary) to lean out the now overly rich mixture caused by the completely closed choke blade.
Please don't attempt to adjust the choke coil or adjust the fast idle speed. Or the timing, or the idle mixture, or the primary jets. None of these items will over come a closed choke plate. Instead I suggest you follow my advice in post #12.
It is very easy to test my theory/diagnosis. With a cold engine (overnight sit) remove the top lid of the air cleaner. Start the engine using the proper procedure; depress the accelerator to the floor. The choke blade should snap shut. Crank the engine until it starts. Go under the hood and manually open the choke blade as needed (usually 1/4" - 1/2") to get a smooth running engine which should be at fast idle. Observe the choke plate open as the thermostatic coil heats up. This procedure assumes all attempted adjustments have been returned to their pervious settings. If this diagnosis proves correct contact Holley for help with the choke pull off for your carburetor.

 

I didn’t think that carb had a pull off but after looking at it you are right that is the problem. Unfortunately it has the crappy brass piston type pull off in the choke housing. Those are notorious for sticking. The mid 80s 460 ford trucks used to come factory with Holley carbs and that was always a problem we faced at the dealer. The only way to keep it from coming back as a recheck was to cut the link from the piston right at the linkage in the choke housing and push the piston down into the bore. Then turn the cold idle rpm up about 150 rpm and back the spring tension off on the choke cap. This allows the air velocity over the choke butterfly to crack open the choke and the engine not to load up when cold. I know some of you will say its half assed. But very few of you have dealt with this issue on a daily basis on customers trucks that just want it to start and run normally. Once you have the cold start rpm and spring tension on the cap dialed in, you can’t tell the difference. The ebrock carbs don’t have pulloffs and use this same concept to crack open the choke on cold start.

 

I didn’t think that carb had a pull off but after looking at it you are right that is the problem.

Thank you for the acknowledgment. Like I stated every automatic choke has to have a choke pull off. Some cracked the choke open about 1/4", later systems fully opened the choke for emissions reasons.
I searched the 'net for Holley Avenger parts. I found a picture of the choke body with the pull off piston as an assembly.
https://www.holley.com/products/fuel...ry_components/
There is a fine mesh screen behind the brass nut for the choke pull off's fresh air intake that should be checked for restriction as I noted in my previous post. If ok I would inspect the pull off piston and linkage. It may be stuck because of carbon on the piston groves or in the bore, a worn out piston/bore, or a backfire. Some pistons may have nylon piston rings that could be worn or melted from a backfire. I did not find a choke repair kit rather an electric choke conversion kit that comes with a new choke housing including the pull off piston for $77. Before changing any parts I would follow the procedure I detailed in the last paragraph of post 23.
My overall advice (if asked) would be to install a Quadra-jet. Tune it, and enjoy the smooth horsepower...

 

I tried calling the Holley tech line, but after 35 min of being on hold, I gave up. I also checked my plugs and they look good.

 

Plugs would not be the problem. Check my posts #23 and #25, I think they will help you

 

I understand that the plugs arent the problem. I checked them because oldscutlass replied in post #7 that one of the effects of mu situation would be fouled plugs. As far as the choke pull off, I dont have a clear understanding of where that is or what it looks like.

 

I attached a picture of your carburetor with a labeled parts layout in Post 12. In Post 25 I included a picture the choke housing with the pull off piston. If you remove the black plastic choke thermostat cover you find the pull off piston.
Before any parts are removed or replaced I suggest that any settings/adjustments that may have been changed be restored back to their original positions and the choke pull off fresh screen be checked for restrictions as I outlined in Post 25. If that looks ok perform the diagnosis that I suggested in the last paragraph of Post 23 to verify that we are going in the right direction of repair or replacement of the choke pull off.
If that is too much you can always roll dice on replacing the entire choke control assembly for $77. I included the link to the Holley parts web site in post 25. Myself I prefer to make a diagnostic check rather throw parts at a vehicle. The rest is up to you.
Please keep us posted with your progress and any questions.
Best,
Richard

 

Here is a picture of the choke housing crudely labeled by me.
I Choke housing assembly with the thermostatic black cover removed.
II START HERE FIRST The screen I suggest you remove and carefully clean with parts clear or full strength Pine Sol (wear gloves!)
III Remove this nut to access the choke fresh air screen.
IIII The choke pull off piston linkage. Check here for binding of the pull off piston. It should move freely.
IIIII The pull off piston bore. The pull off piston is inside.

 

Google "choke pulloff"