Holley Carbs Idle Adjustment [Archive] - Chevelle Tech

: Holley Carbs Idle Adjustment


Keith Tedford
Jun 20th, 07, 9:42 AM
Which Holleys have the reverse idle adjustment where turning the screws in richens the mixture up? I'm installing a 650 vac secondary spreadbore and I'm thinking that it might be set up this way.

77 cruiser
Jun 20th, 07, 10:39 AM
What's the list number on the airhorn?

Keith Tedford
Jun 20th, 07, 10:55 AM
List is 8679.

Buzzbomb
Jun 20th, 07, 11:57 AM
Which Holleys have the reverse idle adjustment where turning the screws in richens the mixture up? I'm installing a 650 vac secondary spreadbore and I'm thinking that it might be set up this way.

I am 99% sure your carb has them. Most all spreadbore vac.sec Holleys are reverse idle. Take a look at the mixture screws. Do they have a big top head on them? If they do, and the carb hasn't been messed with, it is a reverse idle carb.

WHen set up right, a 4175 Holley is a pretty darned good carburetor. I know others have had less than stellar experiences, but I bought a used one off of someone for $50, and after a rebuild, it was a great carb. EASY to adjust with nearly all of the regular Holley parts fitting on it.

BTW- don't think that if you can't kill the engine with the mixture screws that the carb isn't working right. The RI Holley's mixture screws are like an airbleed that is controlled by a screw, so no matter where the screws are, the engine will run.

Keith Tedford
Jun 20th, 07, 12:04 PM
The Holley looks to be in good shape but used. I couldn't get to idle right so I cleaned it and installed new gaskets. Might try it out later today and will let you know what happens. Thanks for the info.

rkd
Jun 20th, 07, 12:46 PM
I have a 8007 that has the reverse idle. Got it new in 87 and it has worked fine ever since. It does like to have new secondary plate and bowl gaskets about once a year. I will note that the 80457 I put on has much larger jets in it, and a single stage powervalve, and is noticeably stronger. And thirstier.

Check the Holley website with the list number, or call their techline.

They have one of the best tech lines going.

Keith Tedford
Jun 20th, 07, 6:22 PM
RKD, what jetting do you have in your carb? I would think that it might be somewhat different from a square bore carb.

Buzzbomb
Jun 20th, 07, 7:05 PM
The Holley looks to be in good shape but used. I couldn't get to idle right so I cleaned it and installed new gaskets. Might try it out later today and will let you know what happens. Thanks for the info.

Your carb IS an RI carb..

Remember- that carb will not die when you screw the mixers all the way in. It is VERY sensitive to the slightest movement of the mix screws. It is also sensitive to how much of the transfer slot is exposed. As I stated before, you are controlling bleed air with the mixture screws. I am sure someone will pipe in here and tell you to try a Qjet instead, however, if you take some time to set that carb up right, it will work great. I have a "cam" in my small block, and my 4175 Holley idled fine AND tested cleaner on a state emissions test than the Qjet that was on it. Of course, this was after some fiddling around with it.

Your carb came with the following STOCK setup-

59 jets
8.5 pv
..and a metering plate with jets the equivalent of 78's- ie. 134-27

EVERYTHING on the rear of that carb is interchangeable with a 4160 Holley, and so is everything else except the front bowl/body gaskets, and of course the other main body gaskets. Pump cams, shooters of the same style, jets, pv's, accel. pumps, secondary springs- all of that is interchangeable- which is :cool:

Keith Tedford
Jun 20th, 07, 9:05 PM
Thanks for telling me about the idle mixture screw sensitivity. I put the carb on this evening and everything seemed fine. It idled fine and drove fine. Then as the engine thoroughly warmed up everything seemed to go out of adjustment and it wouldn't idle in gear no matter what I did. I'll have to play with it again tomorrow. Might be that I wasn't careful enough in adjusting the idle mixture screws. If all else fails, I will just re-install the 4010. One pump of the gas and it starts and idles like a fuel injected car. I've never seen a carb like it. The switch was to see if I could improve the gas mileage.
One interesting thing. With the 4010 I get a bad resonance or drone between 1500 and 2000 rpm. With the spreadbore the resonance was almost all gone. I can live with the sound. The switch would be worth that alone.

Buzzbomb
Jun 20th, 07, 9:26 PM
Thanks for telling me about the idle mixture screw sensitivity. I put the carb on this evening and everything seemed fine. It idled fine and drove fine. Then as the engine thoroughly warmed up everything seemed to go out of adjustment and it wouldn't idle in gear no matter what I did. I'll have to play with it again tomorrow. Might be that I wasn't careful enough in adjusting the idle mixture screws. If all else fails, I will just re-install the 4010. One pump of the gas and it starts and idles like a fuel injected car. I've never seen a carb like it. The switch was to see if I could improve the gas mileage.
One interesting thing. With the 4010 I get a bad resonance or drone between 1500 and 2000 rpm. With the spreadbore the resonance was almost all gone. I can live with the sound. The switch would be worth that alone.

If you're putting the carb on a pretty mild engine, it should work with some fiddling around. I started my screws at 2 turns out from seated and went from there, but 1.5 is a good baseline. Logic says that you will then go IN to make the mixture richer from there, but you have to remember that IN is RICH and OUT is lean! For some coming from other carbs, that is hard to remember at first.

As with any Holley, if it continues to not idle right, take it off and check the transfer slot exposure. You shuould also spray the air bleeds with carb cleaner to make sure they aren't plugged. The idle screws HAVE TO BE the ones with the big head, and they really should have the gaskets on the screws. Again, this is because they are controlling air not fuel. A standard Holley mix screw will function as a hole filler, but it won't allow the adjustability of the short blunt end of the original fat head screw. The float level should be dead on also. As you know if you rebuilt it, it needs to be set with the bowl off. The rebuild instructions in the Holley kit are A+ great.

After the good experience I had with my 4175, I wanted to find a 4011 Holley to try. The problem was, I couldn't find one anywhere! The 4011 Holley was the spreadbore version of the "pop top" 4010. For some reason, Holley discontinued both 4010 and 4011 carbs. I hear you about the way a Holley starts. My 4175 could literally sit for 6 months, I could get in, pump the gas twice, and it started right up.

Keith Tedford
Jun 20th, 07, 10:21 PM
I wasn't reading and paying attention well enough to earlier posts. These idle screws have the small heads. I'd better get the right ones before messing around any more. Would anyone know the part number for these screws? Thanks again.
I was searching around and found part # 26-101 large head idle screws. I guess these would be what I need.

Buzzbomb
Jun 21st, 07, 4:23 PM
The RI screws have fat heads, BUT the more important part is that they look differently than the standard idle screw at the NEEDLE end. The standard screws are long and slender, while the RI screws are more blunt tipped and short. Holley might be making a fat head standard screw now, so it might be worth it to confirm they will work before ordering.

One thing you should check is to see if there is a number on the metering block somewhere that matches your carb list number. People sometimes swap them with other Holleys, but they don't interchange. If you're metering block isn't "numbers matching", it will never idle right. Square and spreadbore metering blocks are two different animals (idle system).

If you are using long slender ended mixture screws, the reason why your car is not idling right is that its running too lean. It's getting the set amount of gas, but it's also getting too much air. WHen the blunt ended RI screw is in there, it cuts off more air due to it's fatter end, which makes the mixture richer.

If you're putting this carb on a mild engine, it really should work fine. Like any other carb, it takes a little time to set it up right and correct the mistakes of previous owners.

Keith Tedford
Jun 21st, 07, 5:41 PM
Thanks H.L. I'll keep your advice in mind. You just never know with old parts. I was looking at the 4010 and the idle screws on it have a big head. Might be a reverse idle carb as well. Funny thing was, the car started fine, and ran fine until it warmed up thoroughly and I thought that the new gaskets had done the trick. Then the idle seemed to go for a crap. I put the 4010 back on this morning and the car runs fine. I'll give the carb another look over later when I have some time.

Chrispyterson
Sep 28th, 12, 9:10 AM
BuzzBomb,
I've got an extra 4011.
If you want it, I'll give it to you.
It's been on the shelf for a while so it'll need a new kit. Walker sells a kit that's about 80% complete, but you're better off just ordering the top gasket and using the normal Holley needle/seat, secondary diaphragm, pump, and power valves. The Walker kit had the wrong size secondary diaphragm shaft, black rubber accelerator pump, and inferior needle/seats.