Rich Idle

[Sublime 70]

Hi I was wondering if anyone could help me lean out my engine at idle.
I have a Holley 860 (Pro System) 78 jet front, 88jet rear, power valve is 4.5 512 cu . Timing is 22 at idle and 36 total. I have turned the air mixture screws in , only as far without losing throttle response. Air bleeds are .082 .(more air at idle) Idle is 1000 rpm, still you cant stand behind the car even when you are outside . Other than that the carb is perfect. Any suggestions?


thank you.
Chris

 

[moparleo]

What engine are you working with ?

 

[Sublime 70]

its a 440 stroked to 512 cu.

 

[Chryco Psycho]

Do you know what manifold vacuum the enigne makes at idle in gear ?
What cam grind ?
you need the powervalve rated 1.5 inches lower than you vacuum reading to make sure it stays closed . A long duration cam with lots over overlap will misfire cylinders at idle pumping raw fuel down the exhaust no tuning will change that .

 

[Sublime 70]

Manifold vacuum is 14.5 at idle and the cam is 555 lift 238 duration,
power valve is 4.5 rite now.....may need to go to 6.5. what do you think?

 

[Chryco Psycho]

I would leave the 4.5 in unless there isa stumble going to wide open throttle

 

[Adrian Worman]

Have you got vac to the dist? If so what can you get total? 52deg?

 

[Sublime 70]

no vac to the dist and total timing is 38 deg, comes in @ 2800 rpm total

 

[Adrian Worman]

Mech advance curve sounds ideal, try taking a constant vac source to the can and check your total initial+mech+vac and hopefully achieve 52 deg.
The idea is that the idle, very light throttle and over run burn so much more efficiently due to the extra advance. The vac can is usually adjustable via an Allen (hex) key inserted into the cans hose nipple.
Try it you might like it

 

[Sublime 70]

What vac can are you talking about? , and where would it be located?

 

[Adrian Worman]

On the side of the distributor if you have a regular street unit.

 

[Chryco Psycho]

How is connecting vacuum advance which should be dead at idle going to have any effect on rich idle condition ? You may need to instal a larger air bleed in the idle circuits , there are 8 bleed near the booster in the throat of the carb the inner 4 are for the jet circuit & the outer 4 are the idle circuit , you actually have good vacuum at 14 " the carb is designed as a race carb so it may be tuned for lower vacuum & should have removable bleeds . Often you can buy packs of ten blank bleeds & drill them with a numbered drill set opening them up a little at a time until it runs the best for you

 

[Juan Veldez]

Am I the only one who seen this post and thought "Why did Mrs. Idle name her kid Rich" or "Hey, is that Billy's brother"? Ya all have a great day, and good luck with the fix!

 

[Adrian Worman]

I take you're point Chryco but the original post questioned not a rich idle but eye watering exhaust which is a product of unburnt fuel? I only suggested that more advance would cure it, if that's not good advice please educate me

 

[Sublime 70]

I did drill the air bleeds out to .82 as patrick of Pro systems told me to, still very rich at idle. Next I advanced the timing to the point of pinging..then backed it off........still rich.......sent the carb back to him.....making me a new one. I did borrow one of my friends pro system carbs and all i did was turn the idle screws in a 3 quarters of a turn and the motor was fine........

 

[moparleo]

The vacuum advance unit on the side of the distributor. If you have a mechanical advance only distributor, it will not work properly on the street.