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Old 11-01-2009, 09:31 PM
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holley secondary bog

I have a holley 4150 dp I put 70 jets in the front and 76s in rear, with stock squirters and 30cc pumps. Loking down the carb while running... with just primaries opening the engine is very responsive, but if u stab the throttle it bogs when secondary kicks in. It doesn't seem to be running rich and definately not lean. Anyone experienced this before?

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Old 11-01-2009, 09:46 PM
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i had one do the same thing my secondaries were opening up to soon
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Old 11-01-2009, 09:56 PM
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How do I adjust it... Is it the screw underneath the carb?
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Old 11-01-2009, 10:26 PM
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What are you running this carb on?
CFM?
Automatic or M/T?
Gears?
Vehicle weight?

Let me start by saying that I'm not a fan of mechanical secondaries, especially if it's a street-driven vehicle.

These carbs are designed to go to WOT right off the line ... sort of either "on or off".

It's the "transition stage" (from the moment you tip the throttle blades from the idle position until the booster venturis start feeding from the main jets) that causes bogging.

The "enrichment circuit", which consists of the accelerator pump and power valve provide extra fuel to prevent the bogging during this transition.

There is no easy way to adjust the opening rate like there is with vacuum secondaries (other than with your foot).

So, other than the power valve ... you can tune the accelerator pump cams and the squirter nozzles, and you can replace the 30 cc pumps with the "Reo" 50 cc ... all in the effort to get a longer transition.
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Old 11-01-2009, 11:01 PM
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As 66 GMC said, a lot depends on what this carb is bolted to. Displacement, cam, exhaust, C/R , timing can all affect carb tune. With that being said, a 4150 DP Holley can be tuned to run very nicely on the street with an automatic trans. My 780 DP replaced a 750 cfm 4160 vac secondary on a 350 sbc and is far more responsive and linear than the vac secondary carb ever was. Clean part throttle running and when the secondaries open there is no hesitation, just instant thrust. Are you sure you have enough jet for the secondaries? I'm running 74 primary, 86 secondary. It sounds like you may be creating creating a lean condition when you open the secondaries. JMHO
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Old 11-01-2009, 11:42 PM
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you need to tell us more for sure if you have a stock 305 whit a 850 double pumper no matter what you do you wont fix the bog because you have the wrong carb to start whit
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Old 11-02-2009, 06:14 AM
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To large of shot from the rear squirter.
Longer shot with the pink cam on the first hole.
The Knowledge Base has a lot of info,troubleshooting/tuning articles.
http://www.hotrodders.com/kb/carburetor
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Old 11-02-2009, 07:18 AM
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It's a 650cfm mounted on a single plane high rise holley intake. Don't know a lot about the motor just that its a 355 sbc and has 10.5:1 compression with 292 duration cam, long tube ceramic headers. Msd 6al box, pro billet distributer, blaster 3 coil, Msd super conducter plug wires, and accel plugs. This all backed by a 3000 stall and 400 turbo. This is in a 78 full size 4x4 half ton pick up. Not possitive about gears but think they are 3.73. I was told the motor dynoed out at 450 hp so must have some head work done too but don't know anything about that.

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Old 11-02-2009, 05:11 PM
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There are three going against you.
1. It's a heavy truck
2. 373 gears are fine. Depend how large the diameter the tires are. That will affect the final Gear ratio. If too large that will make it bog worst.
3. You are using a single plain manifold. You should of use 180 degree high rise dual plain manifold.

Last edited by lg1969; 11-02-2009 at 05:16 PM.
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Old 11-02-2009, 05:24 PM
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Im happy with the top end power I get from the single plane as I don't use it for off-roading. As for tires I have 33's right now plan on lifting the truck putting 4.10's in it with 38's.
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Old 11-02-2009, 07:13 PM
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And you do not need a double pumper carb IMHO.

Vince
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Old 11-02-2009, 09:32 PM
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Quote:
302 Z28 And you do not need a double pumper carb
yeah i would go whit a 600 cfm vacuum list 1850 or at the most a 750 list 3310
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Old 11-03-2009, 09:35 PM
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I'm a big fan of the double pumper... a buddy of mine has basically the same build but a 400sbc in an olds cutlass. He has a vac secondary carb and even with my trucks bog off the line I can out run his car all day long. We have same gears he has posi and mine open. Just never had seen anyone have good luck with vac secondaries. I would much rather just find a fix for my bog problem!
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Old 11-03-2009, 09:47 PM
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Accelerator pump shot is too small, causing a lean hole in the fuel curve. It is worse on single plane intakes used with too low a rear gear ratio along with too large a tire OD. Sound familiar??. you need to increase the size of the shooters(pump nozzles) and possibly change the pump cams too. Buy the pump cam assortment and get the next couple of sizes of shooters and test it out after each change.

I would expect you to need a 31 shooter up front and 33 or 35 on the rear, with a pink cam on the rear. Front cam white, pink, or orange.
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Old 11-04-2009, 09:10 PM
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Quote:
Originally Posted by ericnova72
Accelerator pump shot is too small, causing a lean hole in the fuel curve. It is worse on single plane intakes used with too low a rear gear ratio along with too large a tire OD. Sound familiar??. you need to increase the size of the shooters(pump nozzles) and possibly change the pump cams too. Buy the pump cam assortment and get the next couple of sizes of shooters and test it out after each change.

I would expect you to need a 31 shooter up front and 33 or 35 on the rear, with a pink cam on the rear. Front cam white, pink, or orange.
I still plan on trying all of this but come to find out my rockers were loose... As you probably know this will cause a pretty big bog. Haven't driven it yet but just reving it from stand still it appears to run ALOT better already!!
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