I put a 1977 460 in a 1979 3/4ton and I cannot get this motor to idle down. The facts are I put a early 429 timing chain and gears on this 460 to get away from the retarded timing. I took all of the emission/smog equipment off. There seems to be no vacuum leaks and all ports are capped off. I sprayed wd40 all around this motor checking for leaks and it made no difference in engine run. The only thing leaking is around the bottom of the automatic choke on the intake manifold but this should make no difference because it runs off exhaust. (I now use manual choke) I am using a brand new holley carburetor and have open headers. When you shut the key off the motor diesels itself (keeps turning over). The primary and secondarys in the carburetor close all the way indiacting no vacuum leak. The motor is timed now and the vacuum advance is working although acts weird when you take the vacuum from the distributor the timing will retard itself. Does anybody have any ideas/suggestions I could try?? Thanks

 

I also forgot to mention that the idle screws are all the way in and wont slow anything down to where it should be running. Throttle is all the way backed off also.

 

Float levels and idle mixture set correctly? What's your initial timing?

BTW, vacuum going to the distributor is vacuum advance. Removing vacuum from the distributor should retard the timing.

 

Sounds like you are doing two things wrong. First you time the engine with the vac advance hose removed and plugged off. Second the vac advance hose goes to a ported vacuum source; meaning there is NO vacuum at idle.

The idle mixture screws should start with a basic adjustment of 1 1/2 turns out and the rpm at approx. 650 w the vac adv line off and plugged.

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first thing the reason for the timing change is because you either have the advance line hooked into the manifold itself or the bottom port on that holley(Full Vacuum sources) if want to change that, hook the advance to the upper vacuum port which will only have vacuum when you open the throttle.

you didnt say anything about your idle set screw, is it all the way out???? try turning in the idle mixture screws a 1/4 turn each also. you should be able to turn one side down until the you hear the idle change them come back out a fraction, repeat on the other side

 

Sorry i forgot to indicate that i currently have the idle screws nearly all the way in. Which in reality the motor shouldnt even run like this. But i did time the motor with the vacuum blocked off. But 1 thing you said that the vacuum should not be running at idle. I currently have the hose running to a bottom port on the holley which DOES give vacuum on idle. It originally ran on a ported vacuum switch but the threads were bad and leaking antifreeze so i ran it directly to the carburetor. You also said that i could run it on an upper carb port to only get vacuum with some throttle? Would this cause it to run rough on idle though? thanks guys

 

Disconnect your throttle linkage at the carb and see if that makes a difference. You said you changed the carb. Possibility that the linkage is keeping it front idling down?

 

meant.. from idling down..

 

The throttle is backed all the way off

 

The dizzy should not have vacume at idle, IT HAS TO BE PORTED.

 

Lets start from scratch. Starting with a warm engine. Start the engine and then with the vac advance hose disconnected and plugged.
Disconnect your throttle linkage so that's not an issue; holding the throttle slightly open.
Set your timing to spec. Stop the engine.

Make sure your choke is full open and the fast idle cam IS NOT engaging the adjustment screw.

Turn your idle mixture screws in lightly till they stop then back each one out 1 an 1/2 turns. Start the engine.

If it won't idle turn the idle speed screw in till the arm moves slightly. try starting it again. Repeat till it keeps running.

Adj the idle speed screw till the rpm is near 650. Then you can start adjusting the mixture screws for smooth idle and highest vacuum; lowering the speed accordingly keeping in the 650rpm range. It might take a few back and forth adjustments to get it best.

When you are happy with the carb then reattach the ported vac hose. The engine sound and speed should stay the same. If it changes double check to verify you have NO VAC at idle.

Reconnect the throttle linkage making sure there is free play and it isn't holding the throttle plates open.

The only thing left is to set the choke and fast idle adjustments. You can manually move the choke cam to the higher notch and adj the fast idle speed screw, on the choke side of the carb, to specified rpm, 1200 or so.

Then when cold turn your choke cap to set your cold start position.

Sorry I don't have the specs but we don't know what model Holley you have and I don't have those anyway.

My apologies if I have left anything out; doing this from memory.....

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I have seen those holleys hold the primaries open by the fast idle adjustment screw. Even if the fast idle is totally off if the screw is too far in then it won't let the primaries close. Have you verified that the primaries are actually closed or are you assuming so because the screw is backed off? If your screw is backed off but the throttle stop isn't hitting the screw then you have a condition to address elsewhere. It sounds to me like your fast idle adjustment screw needs backed off. If your throttle is open far at all on a holley you run in the transition circuit and then the idle screws affect nothing and you get a nasty flat spot off idle. Verify that the throttle plates are actually closed, and hitting stop screw before you go anywhere. With the throttle plates open at all your vaccuum advance is getting vaccuum and you aren't isolating your idle circuits so you will never get it right.