Holley 4160 Question: Stumble off Idle...?
 

Well friends, I'm having a bit of trouble getting my new motor dialed in. I'm running a:
355cid SBC
-9:1 Compression
-#882 Heads
-Stock Cam
-Edelbrock Performer Intake/Hedman 1 5/8 Long Tube Headers

Now, the only vacuum ports I'm using is: Manifold Vacuum (for distributor advance) and then the charcoal canister and PCV port. I had my friends dad look at my carb, and he got it all dialed in, but he said that it's leaking raw fuel into the intake, because when he turned my idle mixture screws all the way closed (lean), he said it was SUPPOSED to die..but it didn't (but the idle was REALLY rough). At first, he thought it was a vacuum leak, but we checked and I have a solid 20" at idle. What happens is, when I press the gas off idle, it basically stalls, THEN goes. Right now, the timing is at 14º advance @ 750rpm, and it still is running like crap. He said for me to get my carb rebuilt, but the carb is BRAND new. Any ideas? ANY help is appreciated! Thanks guys!

Re: Holley 4160 Question: Stumble off Idle...? (TIMSPEED)
 

honestly... throw the holley out. i had nothing but problems with it. I bought a demon and it works perfect. just adjust the mixture screws and it runs like a champ.

Re: Holley 4160 Question: Stumble off Idle...? (TIMSPEED)
 

with a stock cam you need a holley 4165, which is a street replacement for the qjet. There are other choices, but not a stock 4160.
the 4160 is a race carb. it can be made to work; i'm sure everyone here will chime in on details if you are stubborn or can't afford a better carb. i've never used the 4160 'cause i've never owned a race only car.
.
EDIT Kudos to Wayne for picking up my mistake! i was thinking 4150 just like wayne said.
As a result, there will be no charge for my advice! LOL


[Modified by Matt Gruber, 9:19 AM 4/28/2003]

Re: Holley 4160 Question: Stumble off Idle...? (TIMSPEED)
 

What are your jet sizes, accelerator pump part number, and float level settings.
Also, check the power valves for blow out. They may be leaking.
Check the accelerator pump for proper adjustment (zero lash), in fact baseline everything and start from the beginning. Or get an edelbrock carb. :D

I don't agree about the demon carbs. My experience with them has been very negative. Out of the box, everything was adjusted wrong. Way wrong, not a little. Not that I doubt the other poster's experience. Just giving my 2 cents.

Your engine doesn't seem to warrant a 4160 (troubles/tuning). I'd swap it for another carb.

Re: Holley 4160 Question: Stumble off Idle...? (TIMSPEED)
 

The other responders may be mixing up 4160 with 4150. 4150 is a double pumper, tough tuning and really a race part. 4160 is a vacuum secondary Holley, generally a very easy tune and a carb that came stock on my '67 and many other Chevys.

Sounds like your power valve is malfunctioning and dumping fuel at all times. Replace the power valve. If it is not a new carb, it probably wouldn't hurt to put a rebuild kit in it either just so you know everything else is good.

Re: Holley 4160 Question: Stumble off Idle...? (L79vette)
 

It's a brand new Part #80460, now Holley says that they have a special thing to keep the Power Valve safe in the event of a backfire...and mine backfired through the carb as I was first starting up this new motor...so, should I put in a new power valve?? Or Power Valve Diaphragm?

Re: Holley 4160 Question: Stumble off Idle...? (TIMSPEED)
 

Make sure that you aren't uncovering too much of the transfer slots. Doing so causes the engine to idle on the main circuit instead of the idle circuit. The fact that the idle mixture screws don't have any affect suggests this possibility. Try turning the idle mixture screws out 1 1/2 turns on both sides and then turn down the idle speed screw. If the problem is exposed transfer slots that should fix it.

Re: Holley 4160 Question: Stumble off Idle...? (Vetterodder)
 

1 1/2 turns out from all the way LEAN?? How low should I turn my idle? 750rpm in drive "feels" smooth. Hopefully that trick'll work. I CAN'T believe this carb is needing a rebuild, it's seriously BRAND NEW (except for that backfire, but Holley says backfire's won't harm them)

Re: Holley 4160 Question: Stumble off Idle...? (TIMSPEED)
 

Read Lars' Holley tuning paper. I put a brand-new-outta-the-box Holley 850 double-pumper on my 468 a coupla months back. It ran like crap. I emailed Lars, read his paper and followed his advice. Now that 850 runs perfectly. Shoot him an email, you'll be glad you did.

Brett

Re: Holley 4160 Question: Stumble off Idle...? (Brettmc)
 

ok, how do I get ahold of this Lars guy?

Re: Holley 4160 Question: Stumble off Idle...? (TIMSPEED)
 

Email him at lars.grimsrud@lmco.com or send him an instant message or page him thru the C3 forum.

Here's a link to the Holley tuning paper:
https://www.corvetteforum.com/techti...=108&TopicID=3

Brett :thumbs:

Re: Holley 4160 Question: Stumble off Idle...? (Brettmc)
 

Thanks man! :cheers:

Re: Holley 4160 Question: Stumble off Idle...? (TIMSPEED)
 

You may have to adjust your floats. i had the same problem with a holly 650 dp and i found that my primary fuel bowl was getting a little too full, and when i would smash the gas a little too much gas would dribble into the intake along with the correct amount which made it pause a little then it would come out of it.

If its not your powervalve....Check you floats.

Re: Holley 4160 Question: Stumble off Idle...? (L79vette)
 

Right, had my part numbers mixed up.
The lars paper is the way to go. Learning how to fix one thing is okay, but the key to keeping a holley happy is to Understand how the Entire carb works as a system for metering fuel.
Good Luck.

Re: Holley 4160 Question: Stumble off Idle...? (TIMSPEED)
 

Yes, from fully closed turn them counterclockwise. 1 1/2 turns is just a starting point and you may get a better vacuum reading with more or less. Try to keep the idle as low as you can and still be smooth in drive. Older Holley carbs (those produced more than about 10 years ago) could have their power valves damaged by backfires but that shouldn't be an issue with yours.

Re: Holley 4160 Question: Stumble off Idle...? (Vetterodder)
 

Well gang, I think this video sums basically everything up
www.timspeed.com/TruckRun1.wmv
All I did was swap my primary jets from #62 (stock) to #64, as per Holley's instructions. But the funny thing is, I did that last night...then this morning when I started my truck, on the way to work, I had a TINY stumble...isn't that weird? I made NO changes to the carb in any way....hmmm...

Re: Holley 4160 Question: Stumble off Idle...? (TIMSPEED)
 

Small changes can yield large effects in carbs. Glad it's runnin better!

Brett :thumbs: