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Holley Won’t Idle Down

14K views 67 replies 16 participants last post by  Reelysalty 
#1 ·
750 DP with HP main body very gassy at idle (mild cam)

No secondary slot exposed so I open w/screw to create square as Holly tech suggested.

Now, carb won’t idle below 1500 or so.

What have I done wrong ?
 
#6 ·
View attachment 618220

Salty, Bruce is referring to your primary idle screw that is accessible on the left side of carb. Not underneath like the secondary set screw is. I have the same carb as you. I'm sure you just misunderstood him.
Gotcha,

Before I messed w/secondary transfer slot, neither front or back slots were showing. I could control idle with idle screw and had normal 4 corner idle screw adjustment. All four out 1.5 turns. Gassy smell at idle.

After cranking rear screw a lot (first time moved, factory setting) I have a square secondary transfer slot.

Static idle screw is now ineffective. I can control idle RPM w/mixture screws, but that ain’t right !
 
#7 ·
Re: Holley Won’t Idle Down

I had the same problem with a 4160 Holley with the gassy smell. Stunk my whole garage up. I rebuilt it with the trick kit. It fixed my hesitation problem but not the gas smell. So I replaced it with the 750 dp. Slight adjustments to the AF screws on the corners and it runs perfect.

Not sure how old yours is, but after learning a lot about holley carbs from my first one, I feel pretty confident with my new one. They are fairly easy to work on.

Do what you can to it and if nothing seems to work, put it on the shelf.
 
#51 ·
Re: Holley Won’t Idle Down

I had the same problem with a 4160 Holley with the gassy smell. Stunk my whole garage up. I rebuilt it with the trick kit. It fixed my hesitation problem but not the gas smell. So I replaced it with the 750 dp. Slight adjustments to the AF screws on the corners and it runs perfect.

Not sure how old yours is, but after learning a lot about holley carbs from my first one, I feel pretty confident with my new one. They are fairly easy to work on.

Do what you can to it and if nothing seems to work, put it on the shelf.
did uget rid of the gassy smell after going to 750
 
#9 ·
Re: Holley Won’t Idle Down

Have you knocked a vacuum hose off ? is a carb gasket ripped ? a large vacuum leak on a carbed motor will act like an IAC on an EFI motor if its big enough.

IAC=Idle Air Control
 
#11 ·
Re: Holley Won’t Idle Down

NEVER hold the secs open if the carb is not a "4 corner idle model". The idle screw is to keep the secs throttle plates from binding in their bores, NOT to compensate for idle issues.

The ONLY time the secs are used to set idle is if the carb is a dedicated 4 corner idle design, most are not. The correct way to set regular secs is to back the plate positioning screw out a bit, so the secondary plates can totally close in their bores, then, set the screw to open the plates 1/4 of a turn, NO MORE. All this is made to do os keep the secs plates from binding in their bores at idle.


Also, using the secs to idle the engine on a 4 corner idle carb is tricky, the secs operate a bit differently, the engine would have to have a very long late intake valve closing time, very radical, to actually need secs idle help, so, most 4 corner carbs that aren't applied correctly, do not need the secs to be open to get a good idle, doing so can mess the whole thing up. Close the secs, set them like the regular carb, and try that.


One thing I do when I do with a Holley is to set the primary idle transfer slots to .020 open, with the idle screw, then, run a scribe across the front UPPER edge of the plates in their bores. This line is where the plates need to be for correct idle transfer slot positioning, and, you can see the lines and plate positions from the top of the carb down the bores, not having to pull the carb off the manifold to see the slots.
 
#13 ·
Re: Holley Won’t Idle Down

Put the secondaries back where they were. It'll never idle down with the secondaries open. I tried the slot thing and it won't work. Open the front to where it should be, and close the rear down till the speed is right.
 
#15 ·
Re: Holley Won’t Idle Down

If you are using full manifold vacuum on your distributor, and haven't taken steps to limit total vacuum advance, you may have too much timing advance at idle. Took my a while to figure that out on my car. Look at Dave Ray's posts on the subject over in the Ignition forum.
 
#16 ·
If you are using full manifold vacuum on your distributor, and haven't taken steps to limit total vacuum advance, you may have too much timing advance at idle. Took my a while to figure that out on my car. Look at Dave Ray's posts on the subject over in the Ignition forum.
Idles fine w/40’ full manifold vacuum. My adventure started trying to cut down on gassy idle smell. Car has mild cam yet is an eye burner compared to my much stronger cammed SBC, which also has full vacuum Advance, same carb set up. Plugs in both cars are grey/white.

BTW, heavy idle timing allows more time for gas to burn in combustion chamber rather than being discharged out exhausts. Also makes for a cooler running engine, temp wise.

Chevelle has Rhodes lifters which are supposed to alter cam idle characteristics. I wonder if they are allowing unburnt gas out at idle to smooth idle quality ?

I have great respect for Mr Ray and always appreciate his thoughts. I’ll respectfully disagree on vacuum Advance.
 
#19 ·
Re: Holley Won’t Idle Down

reely, that rear transfer slot should just "peek" out from under the blades. That's what you did wrong, you need to see like .005-.010" of it is all, NOT any more. Dave Ray said .020" on the primary, maybe it's 20 thou too. I never measured it, did the "just peeking out" thing on the secondary transfer slot, and it seems to be perfect. My Holley's kick ass.
 
#21 ·
Secondary transfer slot is closed (barely) and idle is back to normal, gassy.

For those of you who want to fiddle w/ STS adjustment w/o constantly removing carb use a screw like below and a modified distributer weight spring to hold tension. I believe screw is from MSD vacuum Advance delete kit. This works as long as intake flange doesn’t protrude past screw area.

Not my original idea !
 

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#23 ·
You don't want secondary transfer slot exposed at idle, that is dead wrong!! Only primary transfer slot. Set primary idle screw so the slot appears as small square. Then adjust idle speed with the secondary idle screw. I always put the secondary idle screw bracket on my holleys.
 
#24 ·
Re: Holley Won’t Idle Down

Do you know how much overlap your cam has?

I have a big overlap cam (no idea how big, the PO put it in and just know it's big) and no matter how I try, I can't tune the stink out of it. It is just part of having a larger overlap cam.

My solution for my stinky engine will be a new cam. :thumbsup:
 
#25 ·
Do you know how much overlap your cam has?

I have a big overlap cam (no idea how big, the PO put it in and just know it's big) and no matter how I try, I can't tune the stink out of it. It is just part of having a larger overlap cam.

My solution for my stinky engine will be a new cam. <img src="http://www.chevelles.com/forums/images/smilies/thumbsup.gif" border="0" alt="" title="Thumbsup" class="inlineimg" />
Cam is 228/238 LS 114 mild cam idles 750-800 slight body shake

Thing is my 383 has 233/241. 110 same carb, timing and same MSD 8360 and burns much cleaner, smell wise.
Idles 1000 slight body shake. 13” vacuum at idle.

Smelly 396 has 750 DP, HP mid body, progressive linkage delete, idle timing 25 + 15 vacuum Advance. 15” vacuum at idle

Both cars have clean plugs

IMO, 396 just isn’t hot enough to be so smelly. OTOH, 383 w/cutouts dumps most under car, a little out back while smelly dumps out cowbells, right in my face if I bend over.

Maybe all perception !
 
#28 ·
Re: Holley Won’t Idle Down

Kerry, just to be perfectly clear, I was taught to set the sec blades so the transfer slot *just* peeks out from behind the throttle blade. Not 20 thou, just a freckle.

IS this incorrect, none of the slot visible? Was told the slot just barely visible helps tip in. There's a pic here somewhere I am certain of it.

My idle was always less stinky with retarded timing.
 
#32 ·
Re: Holley Won’t Idle Down

Kerry, just to be perfectly clear, I was taught to set the sec blades so the transfer slot *just* peeks out from behind the throttle blade. Not 20 thou, just a freckle.

IS this incorrect, none of the slot visible? Was told the slot just barely visible helps tip in. There's a pic here somewhere I am certain of it.

My idle was always less stinky with retarded timing.
It does depend on the particular engine and camshaft. But there is a reason that the secondary transfer slots are higher in the bore than the primary.

Most of the time, start with the secondary open 1/4 turn from fully closed, so that the blades are not "sticky", and the primary open so the transfer slots are square. If this gives you too low an idle speed, then increase the secondary opening. If the idle is to fast, close the secondary 1/8 turn. If still too high, close the primary, but you need to keep the primary transfer slots exposed at least a small amount. Not closed off completely.

If you need to open the secondaries to increase idle speed to the point that the secondary transfer slot is exposed, instead open the primary more. Keep the secondary slots not exposed. This is a "back and forth" adjustment, between the secondary and primary, and you may open the primary a fair amount, as long as the mixture screws stay responsive. The primary transfer slots are ideally where the fuel should come from as you transition from idle to off idle, as that is the side of the carb that opens first.

If you end up with the primary at the maximum exposure of transfer slot which still keeps the mixture screws responsive, and your idle is still low, you then need to open the secondary more. If you end up to the point that the secondary transfer slot is exposed, then at that point you could set the primary and secondary for the same amount of transfer slot showing. This is most common with race engines, and/or when using dominator carbs.
 
#29 ·
I wonder if there's a right/wrong way or if it depends on the carb.

I learned to set the primary at 0.020 and the secondary to just barely closed, start & warm up the car, and then adjust the idle speed with the secondary if it is too low or close the primary if idle is too high.

On the Prosystems carb I have now, I was told to keep the slots even. I started with 0.020 on both slots and had to turn both in just a little to bring the idle down.
 
#30 ·
At suggestion of several, and since I have an accessible secondary stop screw, and it’s a rainy, boring day, I opened it up a little on cold start.

Opening secondary did not raise idle speed, cold or warm. Opening DID improve idle quality cold and might have improved cold off idle driveability which has always been a problem.

If adding a little air/fuel thru secondary improves above, does this mean engine was slightly starved previously ? Even tho rich exhaust clearly indicates un-burnt mixture ???

No choke on carb.

Thanks!

(Same gassy smell I’ll accept as penalty for a great rumpty-rump
idle sound)
 
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