Engine Help needed: Idle issue

Mystang66 · Jan 5, 2021

Still having problem with my idle. The car is idling at 2K when warm. I checked the vacuum with a gauge and it is floating between 18 & 19. I’ve sprayed starting fluid around the intake and carb with no effect. If I pull the vacuum advance on the distributor, the engine revs higher. The distributor can’t be adjusted enough to reduce idle enough. Distributor was set at TDC to begin with. Starts right up and runs fine other than the idle issue.

Engine specs: recent rebuild. 1985 302 HO, mild cam, HEI distributor, Holley 4160 carb, headers.

Deleted member 215073 · Jan 5, 2021

I don't think timing is your issue.

Have you adjusted or tuned your carburetor?

7991LXnSHO · Jan 5, 2021

Are you trying to set idle speed with the distributor? That’s not how carbureted engines are supposed to work.

How your idle speed goes up when a vac line is open tells me your mixture screws are probably not set right, or the floats are too high and letting extra gas in.

What model of 4160 is it? The numbers should be on the choke horn. With that info, we should be able to tell you how many turns the mixture screws start out at. Then you can get it fine adjusted at proper idle speed with the vacuum gauge. It also sounds like the idle speed screw or the high idle speed screw are too tight.

Please set the ignition timing with the vac line off of the advance and plugged. By 2000 rpm, the mechanical advance should have started, so you will need to check timing again after the carb is running better.

General karthief · Jan 5, 2021

There are a lot of moving parts when using a carb,
Set timing 10*-12*- 14* wherever it likes, I set it to achieve the highest vacuum reading,
Turn the idle screw till it does not touch the lever, then turn it back till it touches the lever then another quarter turn
Make sure the choke is open and the choke lever with the adjust ment screw is not engaged
This is the starting point I used when starting with a carb of unknown condition.
One thing that can cause a carb to idle high is a misadjusted choke and/or kick up lever.
Most carb manufacturer have a 'tuning guide'.

Mystang66 · Jan 5, 2021

7991LXnSHO said:
Are you trying to set idle speed with the distributor? That’s not how carbureted engines are supposed to work.

How your idle speed goes up when a vac line is open tells me your mixture screws are probably not set right, or the floats are too high and letting extra gas in.

What model of 4160 is it? The numbers should be on the choke horn. With that info, we should be able to tell you how many turns the mixture screws start out at. Then you can get it fine adjusted at proper idle speed with the vacuum gauge. It also sounds like the idle speed screw or the high idle speed screw are too tight.

Please set the ignition timing with the vac line off of the advance and plugged. By 2000 rpm, the mechanical advance should have started, so you will need to check timing again after the carb is running better.

It’s a Holley 80457S

General karthief · Jan 6, 2021

Those are easy and they have tuning info on the webpage.

7991LXnSHO · Jan 6, 2021

Then there are no goofy or sealed smog era idle mix screws.

Tuning Your Holley Carb Made Easy

With the continued development and popularity of the Holley four-barrel carburetor, knowing how to properly tune one is very important.

www.hotrod.com

Mystang66 · Jan 7, 2021

JMGlasgow said:
I don't think timing is your issue.

Have you adjusted or tuned your carburetor?

I’ve reset all the screws per Holleys directions. I’ve ensured the fast idle is adjusted to keep the valves closed. I’m going to try starting it tonight and see what happens.

Mystang66 · Jan 7, 2021

I’ve reset all the screws per Holleys directions. I’ve ensured the fast idle is adjusted to keep the valves closed. I’m going to try starting it tonight and see what happens.

Deleted member 215073 · Jan 7, 2021

Did you adjust the float levels? Out of curiosity what is you timing set at? Do you know what your fuel pressure is?

20 years ago before I learned to hate carburetors I never had any issues setting the idle speed with a Holley.

Mystang66 · Jan 7, 2021

JMGlasgow said:
Did you adjust the float levels? Out of curiosity what is you timing set at? Do you know what your fuel pressure is?

20 years ago before I learned to hate carburetors I never had any issues setting the idle speed with a Holley.

I haven’t adjusted the float levels. I’ve left it as it came. Don’t know the pressure. I’m running the standard mechanical fuel pump. It’s new as well.

7991LXnSHO · Jan 8, 2021

If it is about old enough to not use a car seat, the Holley should have externally adjustable floats and fuel bowl sight level brass plugs. Do not buy clear plastic ones.
If it’s a newer Holley, it should have sight windows and a different, still easy float adjustment method.

Mystang66 · Jan 9, 2021

I’ve been able to get it adjusted to about 15/1600 rpms in P and about 900 RPMs in D or R. Not sure if that is close to normal or not?

Engine Help needed: Idle issue

Mystang66

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7991LXnSHO

wanna catch the space herp

General karthief

wonder how much it would cost to ship you a pair

Mystang66

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General karthief

wonder how much it would cost to ship you a pair

7991LXnSHO

wanna catch the space herp

Tuning Your Holley Carb Made Easy

Mystang66

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Mystang66

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