Engine Idle Issue After carb swap

[ep67bro]

I have a 302 in my 73 that had a stock Motorcraft 2100 carb and cast iron intake on it. I just switched to a edlebrock performer 289 intake and a Holley 600cfm 8025 carb. I did a bunch of work to the cooling/heating system at the same time.
The issue I have is the truck will start but has a very high idle. I backed the curb idle adjustment all the way off and it still idles well over 1000 rpm. It was even worse when I had the vacuum advance hose connected from the carb to the dizzy. I think my timing is off but cant get the truck to idle low enough to check it. Back story on the carb is it is a carb I had on my 289 in my 67 bronco for years always worked good just switched it out for a Truck avenger when I started off roading more. Drained it, put it in a box and stored it until now. could it be a problem in the carb? Dizzy problem? Timming way off? Any ides would help.

On a side note I have the vacuum port for my powerbrakes and auto trans in the plug on the higher runner of the intake, is this ok? I noticed that in one of the other broncos I had it was in the lower runner? any difference?

 

[Justafordguy]

Sure sounds like a vacuum leak to me.

 

[Fairlane514]

Have you checked your high idle screw? Is your choke functioning?

 

[Bferrari]

The vacuum port you are using should be fine for your booster. Are you running a choke? Sounds like the cam for the choke on the right side of the linkage may be holding the butterflys open and not letting it retun to idle. You have any pictures? I would also check the floats if the carb hasn't been run in a while.

 

[blubuckaroo]

Check your throttle linkage to make sure it is letting the throttle close completely. A different carb will put the throttle lever at a different distance from the firewall or bellcrank. Some of the linkages have an adjustable length that make it really easy.

 

[ep67bro]

Idle screw is backed all the way out. The throttle linkage is good it doesn't change if I disconnect it.
I hope to have some time this afternoon to play with it and check the other ideas people had. I will also take a pic. Thanks!

 

[dave67fd]

If your truck ran and performed fine prior to the carb swap then your timing should be fine unless you played with the distributor.

If it's been sitting awhile you should first confirm the idle adjustment (disconnect linkage completely to eliminate that) then readust your idle mixture screws. If you don;t know how read this.
http://www.caribbean-joe.net/vette/instruction/htune.pdf

 

[ep67bro]

I pulled the dizzy to replace the intake and clean things up. So I am sure the timing is off a little. But it will check more this after noon.

 

[phred]

Holleys have another idle screw on the choke cam. Back that screw out and the idle will come down. There is a video on this adjustment in hollers web site

 

[67RT]

I agree with above. Also, Set initial timing with vacuum gauge to get best vacuum with advance plugged, then do the same with idle mix screws, making sure both are out the same number of turns. Start at 1.5 turns out and go from there. I usually take them out a half at a time until vacuum stops rising, then back in a quarter. Then readjust idle speed screw.

 

[Stingray240cs]

This may not relate to your Holly, but for my edelbrock 1406, it was the throttle blades on the bottom of the carb. They needed to be slightly adjusted because they wouldn't close all of the way. Good Luck!

 

[ep67bro]

Thanks for the input. I found three problems
1 the linkage for the choke was bound up and was staying closed
2 the power lead for the electric choke was not getting power
3 the timing was way off
I fixed all the above but still need to tweek the timing as I couldn't really see the timing marks on the balancer. Need to get under the truck and clean it up.
Got it idling at 950 rpm
No hesitation but doesn't seem like the secondaries are opening at full throttle. Hopefully it wont be snowing/ raining tomorrow and I will have a little time to play with it again. Thanks again for the input!!

 

[67RT]

With truck off hold pedal to floor with something and then go make sure throttle is fully opened..

 

[jckkys]

A stock 302 is never going to use the air flow capacity of a 600 CFM carburetor, unless it's a Boss 302. The secondaries will only partially open if the the correct diaphragm spring is used.

 

[broncnaz]

Really if the correct spring is used you should never be able to tell if the secondaries are opening. Its common for people to believe they need to feel them opening but that is really a bog before power kicks back in.
You said the idle goes higher with the vacuum advanc hooked up? Are you running ported or maniolf vacuum? If ported You may still have a vacuum leak or the throttle blades are not closing all the way and your getting enough airflow to create vacuum in the ported advance. Which would be the reason the idle speed goes up.
If your running manifold vacuum then your intial timing is to high.

 

[ep67bro]

Finally had time to mess with this again and every thing is good.
Idles smooth, idle rpm around 600, timing set about 10 deg.
Still has a very slight hesitation off idle but I think the motor could use a new set of points, wires, cap and plugs, might try to do those after I drive it for a while. Truck runs better than it ever has for me. Happy that I did all this work and got good results!

 

[67RT]

Congrats. Feels good. Some things are easier than others. I started my Mopar, which always runs great. The 440 was missing like crazy. I instantly went for a new module, etc. Turns out a spark wire was off. Gotta love it.. Thank god..