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Holley carb.

tileman61

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Bought new 4150 hp 850 double pumper replaced old one same carb just older. Installed it dialed it inane set floats. getting bog when slamming gas Holley told me go higher squirter nozzles did that. didn't do it then they told me it has 6.5 power valve in it. It has a 4.5 in it. so I bought a 2.5 an 3.5 because manifold pressure is between 5 and 7 . Now getting lean pop . Any ideas
 
Smaller acc. nozzles? Maybe ur going too rich. Rear end,engine,cam etc?
 
If vacuum is true, the 3.5 power valve should be close. No vacuum leaks?
If rest of tune is proper (timing,ignition ok, jet size), try a 50 cc accelerator pump if not already. Then accelerator pump cam profile.
Hope it helps
 
Since you pulled the carb off, maybe you have a vacuum leak at the carb base? Also, if the carbs are EXACTLY THE SAME, then the old setup (jets, accel pump, accel pump cam, squirters, power valve, etc.) should transfer over to the newer, identical carburetor.

If you have a "bog" (falls on it's face off idle when you floor it) then it "sounds" like you're not getting enough fuel (or too much air). Since it's a double pumper, we can rule out secondary springs.....which leaves the "squirt" (front or back) too small or a vacuum leak in my opinion.

One more thought... did you modify the metering bodies on the old carburetor & the new carb doesn't have these modifications?
 
I am anxious to know what solves your hesitation problem. I have been edging up on solving the same issue. You most likely know it, but just don't change to much at the same time. If you change something, go back and check the timing, the vac, gap on the second stage at wot. I changed squirters from .40 to .37 on secondary and it seemed to help, changed spring size on distributor and went back to silvers ( strongest). Changed power valve from 6.5 to 4.5 and settled on 5.5 (with plug up front). Changed distributor cam to smaller dia and back again. Everything I have done effected the timing a little. I have not found the "happy" setting. Oh, this was all on a dbl pumper 850cfs.
I have read many articles and posts on setting the Holley up.Haven't given up, but can't seem to tune it in. My carb sits on a 440 with upwards of 600 HP. It may be time to give up on my pride and take it to a race shop. Good luck and I hope we can both find a remedy.
 
Am I wrong guys but with a 3:54 rear couldn't an 850 dblpump be too rich? From not enuf rpm. Not real versed with 4-sped.
 
On my 850 dbl pumper carb (list # 4781-2) on a 451, it ended up running best with 88 jets all around, which is odd because I'm at 5400 feet, and stock jets are 80s. It should have run fine with 80s or smaller for this altitude. It was a high compression motor, with a 509 cam, ported 915s. If it's popping out of the carb, then it's prob too lean. Try going up 2 to 4 steps larger main jets.
 
Holley says bump up air
Bleeder screws on 4 corners 3 sizes reajust idle mixer screws then put in power valve after highest vacuum reading leave #32 squirted nozzles on should cure it
 
There's no way you need a 5.5 PV. Not on a combo like that. But changing that won't help with your issue.
Always start with checking your timing 1st and go from there.
 
Oldbee, I am running 3.73 so I go through the ranges pretty quick, like as fast as I can for another oldbee. 4 spd.
Gary1969rr...Sounds so close my set up. 915, ported, headers, 3" exhaust, Holley 850 with dominator intake, rocker rollers,MSD ignition, cold air intake, larger dia valves, .040 over.......did a valve train rebuild with a Comp Cam Kit and chose a slightly high cam than Comp Cam recommended, but agreed it would give me what I wanted. It is a 491 cam. Looking at the plugs with recent setup showed a little more soot on the ring and darkened ceramic post. I had it at a vac of 13 which calls for a 6.5 PV, but I went with a 5.5 on advise from mechanic. So, I believe I am a little rich. When I adjust the mixture, my timing goes off so I have to find that happy medium. I have switched to ngk 4IX iridium plugs with a .035 gap. Has any one run these? Good, bad, indifferent? I have read nearly every post relative to the type of plug to use. No one particular plug recommended, but Gary, your set up is close to mine, what do you use and gap. It is a lot more sensitive than I thought it should be. Tileman61...are you saying that Holley told you to set the mixture with no power valve and then open the secondary and put in the PV? Gary1969rr....What size squirters are you using? Same in both primary and secondary? Tileman61, I am getting a feeling I am stealing your post. If I am I am sorry. I am only trying to find out what might work for me and apply it to your request.
 
Hi, I sold that RR about a year ago. It used stock squirters, and a 2.5 or 3.5 P Valve. A lower number P Valve will lean it out in the sense that it will take more throttle opening before the PV opens. So it takes a little longer to open, when the vacuum drops off to that level. Adjusting the fuel mixture should have no effect on the ignition timing, unless you are adjusting it with the vacuum advance hooked up. Best to unhook it before adjusting the mixture screws. I was using an NGK plug, seems like it was a 6 or 7 heat range. Also, my motor had dome pistons with the 915 heads, getting it up to around 13 to 1 C/Ratio. That 451 regularly pulled my 3600 lb RR to low 12s at a mile high above sea level!
 
So Gary, do you agree that the fuel mixture should be adjusted via vac and then assemble the pv? I'm going to try the 3.5 pv. I would still like to know about the sizes of the squirters to use on a 440 with Holly 850. I think I'll go back to the 80s on both. One other thing we did not discuss was where do your cars like to run with the level of fuel in the sight glass? Mine likes 1/2 up the glass. To lean when just at the glass and too rich when above the centerline.
 
Have you checked your transition slot. It should look square on the primary side.

Try turning out the idle fuel mixture screws a half turn to see if you're going in the right direction.

You may need more initial timing.

Make sure there's no delay at the nozzles when applying the throttle. Have you tried different cams?

As for your PV, I have 4.5 inches of vacuum at idle and use a 9.5 PV - Street set up.
 
I adjust idle mixture screws for best idle RPM and smoothness. A vac gauge would help, going to highest vacuum.
 
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