Holley gurus come in and talk..

[Larry68GMC]

I've got a 750 dual feed on my new motor, its running really rich at idle, I'm talking watering your eyes rich. I've put different jets in it, it seems to run best with 79's in it, but its real rich. Do you guys know where I can get something to help me tune this thing.

[cableguy0]

adjust the idle mixture down some also put smaller jets in the front and go larger in the rear to make up for it. are you sure the power valve isnt blown?

[bigjimzlll]

do you have power valves installed? is this a vacuum secondary? The jets dont have much to do with the idle quality. The main thing is to adjust the throttle blades so the the just show a little bit of the idle transition slot and to get the enrichment screws set right. Your timing can have a lot to do with idle quality to. Get a vacuum gauge..it sure makes it easier

[ureckme]

I ran a 750 DP, 538 lift 308 dir cam and passed the state sniffer test 4 years running without tuning each time. I would need to know whats in your engine, carb, cam, intake, haeders, etc. bigjimlll is right start by getting a vacume gauge. I learned alot of tricks from some big name oldschool racers. Racecar spelled backwards is (Racecar). I'm sure we can help you.

[Larry68GMC]

Yes I've tried different power valves and its the same thing. I'll play with the idle screws and get me a vacuum guage. Here are the specs on the engine: Dart Pro 1's 200/64cc, with 1.6 roller rockers, 10:2 compression, Duration @50: 224/234, Lobe lift: .310 .325, Lobe Sep: 107 117, Gross lift: 496 518, RPM AirGap, long tube headers, and this Vac Secondary 750. Anyone know any good holley books I could read up on? or do you guys think this carb is to big for me? ..Thanks...Larry

[ureckme]

Your carb. is not to big. We will fix it a little at a time. #1 Put your stock jets or 1 size bigger back in. Set your mixture screws so your vacume is the highest it will get. Set your timing with vacume gauge to get best vacume level. Take reading on vacume. ( Do all this in gear if you have an automatic trans. ) Get a power valve 1 to 2 inches under what your vacume is at idle. Make sure there are no vacume leaks anywhere on your engine. This is a good starting point. Let me know when you have made changes.
Matt.

[ureckme]

Most problems people run in to with holleys is work kinda ok sometimes on stock engins. All out of the box carbs have to be set up to the engine there put on unless its a carb for a specifsic application. Once you put a cam etc. They wont run under 1200 RPMs run so rich it burns your eyes and the metering screws no matter how much you turn them it doesn't change anything. This is a fixable problem, and there is a step by step solution. I start with fileing the front, back, and bottom of the main body of the carb. Holleys are cast and the gasket area is not flat once they get hot the problem only gets worse.
Put in a power valve 1 to 2 inches under what your vacume is at idol.
Once you get it running again set your idol speed down. If it wonts to die befor you get to 700 RPMs theres a fix for that to. Your mixture screws when turned all the way in your engine should die. If it doesn't youll need to go thru the next step.
This is alot of writing for me I have to do this in sections and I can only do it late at nite so be patient.

[ureckme]

This next step will bring low end power and adjustability. What you need is to lean the mixture.
When you have a large cam in your engine it wont's to run at about 1200 RPMs it's running on the main circut in the carb. the trick is to get it back on the idol circut.
Look inside your carb at the primary butterflys if there open more than .040 there open to far.

If you have ever looked at the primary butterflys on a holley carb that came factory on a big block you will see a hole drilled in each butterfly, this is to allow more air, to lean the mixture.

For the hole location you'll have to look in one of the holley books unless someone has a piture of it ( come on guys help me out here ) you with a small drill bit 32ND of an inch and inlarge little by little untill you can turn your idol speed down to around 700 to 800 RPMs and your idol mixture screws will make your engine die when turned all the way in and proper mixture at 1 1/4 turns out.
My truck had a 538 lift 308 duration comp cam passed emissions with a 1.28 max allowed 4.00, idoled at 700 RPMs and would pull a trailer up hill at idol and never got to hot. Hope this helps. Matt

[LONGHAIR]

Does this truck have an automatic transmission?
If it does this may effect you as you try to get the idle down (in gear) . A stock torque convertor will put quite a load on the engine and drop your idle speed way down. Then when you put it back into park/neutral...the idle goes way up.

[cableguy0]

i just had a thought after rereading. check and make sure your secondaries arent opening at idle because of the low vaccum the spring might be the wrong one for your application and if the secondaries are opening even a little bit tuning will be a total nightmare. i also agree with longhair that combo should have at least a 2500 stall convertor or its going to kill the truck when you go into gear

[ureckme]

CableguyO has a point, you should make sure the secondarys stay closed at idol by adjusting the secondary rod on the linkage side of the carb ( Vac sec only ) Hear in Arizona if your idol is to high you'll get a ( Failed ) on the sniffer test. And why not have your engine running correctly, more horse power, better ET. better off the line.
And no watery eyes becouse you just lost to someone with a smaller engine that was set up right! Thanks to everyone who have read this. I do hope that I can help someone with there Holley problems. Matt

[bigjimzlll]

OK....make sure your timing is correct...I find that if your vacuum advance is hooked to full manifold vacuum you can tune the carb much easier.

[Larry68GMC]

Thanks for all the advice guys...I'm gonna go out and try to get this thing running right I'll let you guys know what happens. I do have a 2500 stall, that is what was recommended by the cam guy....thanks..

[wannabeburbowner]

yes this should be in faq's, very good information here. I got my 750 DP running ok on my truck, but I never really did it with a vacuum gauge. I have some tuning to do now. Thanks guys this board is great!!!

[VetteVet]

Hi Larry68
I ran across this site. There's a lot of info on Holley carbs. Go check it out and note the casting number info too.
www.mortec.com/ sfampage.htm
vettevet

[Mel Foye]

You need to get your timing set up, at least the initial and vacumn side before playing with A/F to get a good idle.

The size of the primary jets has ZERO to do with idle quality.

Using a vacumn gauge to set your timing is not a good method. Think of how each of the three timing systems work and the purpose of each and you will see why.

Old gas can cause an eye stinging exhaust because so much fuel passes through only partially burned.

Before drilling the primary plates you need to know where they are in relationship to the transition slot. Usually adjusting the seconday plates is a better way than first drilling the primaries.

The mortec site that was mentioned is a great site and has some real good links also. Good luck. Mel

[ureckme]

No one said time it with a vac gauge, it's to get your vacume up so you can put in the right power valve. you time with a light. Matt

[Mel Foye]

Originally Posted by ureckme

Set your timing with vacume gauge to get best vacume level. Matt.

Mel

[gunnersm8]

holleys, must have 3 things- vacuum gage, a book, and patience.

[67chevemall]

Where does one hook up the vaccum gauge?
Where the pvc goes to the carb?

So use the timing light and the gauge?

[ureckme]

And when your done go back and set your timing, do a plug reading, and fine tune. All this info. is from a pdf you can get from Holley
http://www.holley.com/types.asp?type=9