Searching for a crisp idle
 

pn 0-80513-1 race mechanical secondary 1,000 cfm holley

engine running great, happy with the performance at full throttle.

I don't have a wideband, but I can certainly tell its rich at idle, it idles ok but not crisp. I have to idle at a higher rpm to keep it from feeling like its "loading up".

the idle screws are all 1 full turn out. I tried going much less but gets worse and the engine will die.

i'm no super tuner, probably a boring subject for experts but my question is where and what do I change to lean out or crispin the idle?

the 91 octane premium is all I can get around here, I get some dieseling after shutting the engine off to. hate that.

Im sure others will reply, im not familiar with that holley carb but when adjusting the idle screws you want to use a vac gauge & adjust the screws to get the highest vac reading, or by ear if they make enough of a change. As you do that the idle rpm should increase which will let you turn down the idle screw some which will help with run on. Also check the timing if the idle drops and might be able to increase it a degree or 2 which will also raise the rpm and allow more drop of the idle screw, just be sure no detonation if increasing timing.

Thats not really "supertuned", just a basic explanation of how I adjust the idle screws for highest vac on my cars, q-jets usually want 2.5-3 turns out as a starting point. My 12.7:1 E-head stroker motor would run on a bit on hot summer days and heat soaked, doing the above process all but stopped that and improved the idle... if it still diesels on shut down, just shut it off in gear for an auto or with slight clutch pressure for a manual trans.

First off 1 turn out of the idle mixture screws may not be enough on a Holley.

Question that you need to provide answers for to recive maximum help.

What Cam are you running.
What's your idle vacuum.
What is your initial timing.
What's the motors compression

What Intake is the Carb sitting on.

If your carburetor is a "Race" only carburetor, it probably does not have power valves installed. When these vacuum controlled valves are eliminated, the jetting has to be increased causing a very rich idle. These carburetors are set up to run at full throttle conditions with no regard to idle. Check to see if these valves have been removed and plugged, and the jet numbers installed especially the primaries.

Comp cams hyd roller
GRIND # P8 3317S /3318S HR110.0
DURATION @ .050 INTAKE 242 ROCKER ARM RATIO
DURATION @ .050 EXHAUST 248 1.65
VALVE LIFT INTAKE .540
VALVE LIFT EXHAUST .562 LOBE SEPARATION 110.0
INTAKE C/L 106.0

Vacuum warm/idle/in drive 6.5

Intake is a performer rpm

intial timing is 12 degrees, 36 total degrees total all in at 3,000rpm DUI HEI dist no vacuum advance. (was 16 degrees intial no pinging moved to 12 to see if it helped idle, no diff noted)

472 ci, round port 87cc butler ported edelbrock heads, as I recall flow around 310. so I would say compression 10 to 1

rare oversized exhaust manifolds. 2 1/2" exhaust all the way back with dynomax ultra flow mufflers. h crossover.

(has power valves, blocked the rear. 3.5 in front)

What idle speed ?

Just an observation/question, but does that engine combo need a race 1000cfm carb? especially if its more of a street car? Probably some better carb options for street use.

Is 6.5vac normal for that type of combo? seems rather low for similar builds I've read about over the years.

go back to the 16 initial, or try even more if your starter can take it.

I would open up the Primary Idle Air Bleeds by .004, put in a 5" Primary Power Valve, and
that should allow you to set the idle speed to 850/900 idle rpm.

Tom V.

In my limited experience with the tight 110 LSA cam I was not fan. It seemed fine with headers but with my long branch exhaust manifolds I hated it. I was using a Q-jet and couldn't really dial it in. The exhaust smelled terrible, I had bad nozzle drip that no amount of adjustment would fix. I ended up changing to a roller setup with the stump puller cam. I also modified the LSA on it from 112 to 114. I really like it now.

Granted you have a different cam and setup. Just my $.02

900 rpm in drive right now and don't like it. sounds to fast but lower it sounds like loading up.

I will go back to 16-18 intial timing. only tried 12 thinking it may help the after run at shut off.

air bleeds open up to .004, not sure whats in it right now with those. never changed that.

note that holley calls this a "race" carb not me. must be because no choke provisions and from what I have read here the 1,000 cfm flow is not reality? however holley determines that, 800 cfm probably real world?

this engine has always had the 6.5 vacuum from fresh build. I thought it may have more changing from the victor I had on it to the rpm but didnt make a diff. engine runs great just trying to figure out the idle tuning.

really appreciate the help.

As far as the run-on after shut off, the distributor timing has nothing to do that since no spark from the plug occurs with key off.
My engine used to run-on after shut down also, until I went with full 35 degree initial timing (basically locked out). This timing change obviously resulted in higher idle, and after lowering the idle by turning-in the curb idle screw, (closing the throttle blades more), the run-on stopped completely. With this timing the car is much more responsive in normal driving. I realize that locking out a distributor is not for everyone, and results in harder cranking, but that’s not an issue with the Progression Ignition distributor that I have, which always cranks at 10 degrees btdc no matter what your initial timing is set to.

singleton

yes I should have clarified my thinking regarding engine run off and timing. just meant maybe 12 degrees timing may allow a cooler running engine/combustion chamber to help that. definetly no spark with key off. thank you for the help, this engine likes more timing, i'll go back to that and readjust. going to check those airbleeds as well, new territory for me there. restoration took long enough I even forgot where my timing light was! getting back to funner stuff like tuning and driving and the quarter mile......

curious, are you running a stock torque convertor or a higher stall?

air bleeds
 

9" neil chance street stall converter. 3,000 brake stall.

in changing the primary air bleeds, (have not ever done this) change the idle air bleeds only? leave the high speeds as is?

my carb has #75 idle and #25 high speed.

Give the engine the idle speed it wants...mine loves 950..smooth in and out of gear..crisp idle means nothing in the garage or laneway..what you really want is crisp idle at a stoplight..car responsive ready to go..usually takes a bit more idle mixture richness to achieve that...As others have noted...timing can play a huge part...are you running vacuum advance is it manifold or ported..is your timing steady at idle

What spark plugs you running old Kansas buddy?
I assume your Race carb has huge bypass air holes in the throttle plates?
Most likely too big for your cam and combo

well hello Jeff! If you were closer I would send this carb to you in a heartbeat but I just finished the restoration and want to drive it.

biggest mistake I made was selling the qf carb you built (fixed) for me. man that combo was perfection! in fact, my idle issue i'm dealing with is because I know the way it previously idled with your carb. crisp/clean perfect idle. I sold the victor and carb to go another direction.

my combo now is the exact same one/same engine you coached me "live" at the track and I went from 12.60 to 11.80's all day in 2 weekends with carb jetting and going to pump gas instead of race fuel. nvr forget that. all my friends were there at the track with me that night and were really impressed. including me. it was so cool you were willing to help like that.

ok, so its the same engine, I just swapped to a performer rpm, and went ra exhaust manifolds instead of headers. all else the same. you recommended the carb I have right now. using NGK BKR5ES-11 spark plugs. same ones I raced with that night. in fact still have the old ones.

so NH buddy, recommendations? good to hear from ya! Eric

Haha! Eric! Where's your Kingpin avatar??
You don't forget a thing!...lol
Start by either posting pic looking into carb so I can see what you got or text them to me.
Have you tried Autolite 3924's ?
Maybe pick up 4- cans of Seafoam
I don't recall advising that carb rather you picked one up?

Changed avatar due to a lengthy restoration now new era ha.

not a carb expert nvr thought of looking at those, they do look huge to me from what I recall on my other carbs. I think you had sent me 2 choices on carbs one was an 800 or 850 so yes its on me choosing this one.

have only used the same plugs as always dont mind trying the autolites. seafoam probably a good idea. the engine has only been started for last 8 years so could use it.

will the suggested increase in idle air bleeds and pwr valve change to 5.0 help or do I need more changes? or move to another carb?