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OT - Holley 750 DP tuning

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SHIP4BRAINS

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Discussion starter · #1 ·
HELP!

A few months ago I picked up a 750 holley DP for my F250 to replace the carter POS.

Yesterday I did the swap and finished it today. Started up and idled, after I got the floats adjusted so there wasn't fuel dumping all over everywhere.

I took it out for a test run today...all the way down the block it ran flawless. Crisp off idle, smooth transisition from primary to secondary...etc...headed out of town to open it up...ran great up to 60mph then started leaning out and sputtering. I backed off the gas and it idled ok...then got into it and once again, what I assume to be a very lean condition as it fell on its face. I pulled into a driveway and it died. I popped the hood and adjusted the front float valve up a spin or so and it popped right off...ran down the road then loaded up bigger that $hit...black smoke.... I stopped...gas everywhere. So I went back home and adjusted the floats again. I adjusted both so there is just a trickle or no fuel coming out of the site screw at idle. Took her back out for another run. Once again, a good mile of clean crisp throttle response from idle to WOT....then it fell flat on its face. The SOB has got to be running out of fuel. When it acts up, if I let it sit and idle for a minute, it runs great for a half mile or so then acts up again. It will sit and idle perfecty....no smoke.

The carter didn't have this problem, just others...MANY OTHERS. This carb did sit a few months dry...are the float needles sticking shut? I can't imagine they are as when improperlly adjusted they dump fuel everywhere. Not enough fuel pressure? WTF?!

I know there are some carb tuners out there...

THANKS!
 
#5 ·
You say you "picked up" this carb. Was it on a boat, tractor, dune buggy, drag car, monster truck or Volkswagon?
It may be set up for a race car, therefore needs mucho tuning to run correctly on your F250.
Start with the basics....yes you need to pull it apart.
 
Discussion starter · #8 ·
It is a 3310
Main jets are 68

I pulled both bowls off...both floats seem good.

When pulling the rear bowl off, I see something compltely different than the front...no jets..just a plate bolted in place with special head screws...apparently they don't want you to remove this?
 
Discussion starter · #9 ·
The carb was on a 454 in a Monte Carlo....they previous owner put in a different cam/lifters and the vac secondary wouldn't function properly so we went with a mech secondary carb

Definately not on a VW...

Location is Fort Dodge!
 
Discussion starter · #10 ·
It appears the stock primary jetting should be a 70 - secondary metering plate should be a 21 ( this i need to check ) pump discharge nozzle should be .031 ( need to check ) and the primary power valve should be 65 ( also need to verify.
 
#11 ·
I'll help too but I have a question and then a statement.

Question: What size engine ?

Statement - get that friggin double pumper off of your truck !!!! DP's should only be used on lighter vehicles with more gear, more cam, and a loose torque converter. The use of a second accelerator pump is no good on a haevy vehicle that's being driven around everday. Each time you touch the gas pedal you will squirt to much gas thru the carb and wash down the tops of the cylinder bores, dilute the oil, and cause dismal gas mileage.

With that being said, your symptoms are classic of having a pice of 'smegma' either in a needle and seat or jet. When you stop the engine, the fuel flow stops, and this pise of junk may float away from the needle and seat or jet passages. When running for a few, this piece will travel back into either of these and cause this.

Take off the float bowls and needle and seats.

Better yet, get rid of the carb and get a vacuum secondary one.
 
Discussion starter · #12 ·
Hold your horses there buddy!

Maybe it isn't a double pumper..It is a dual feed. My mistake. There is only one accelerator pump on the primary...none on the secondary...and the secondary is vacuum

Engine - basically stock rebuilt 460...original intake and exhaust...( hack hack, choke, puke...)
 
#13 ·
SHIP4BRAINS said:
HELP!

The carter didn't have this problem, just others...MANY OTHERS. This carb did sit a few months dry...are the float needles sticking shut? I can't imagine they are as when improperlly adjusted they dump fuel everywhere. Not enough fuel pressure? WTF?!


THANKS!
Click to expand...
So, you are saying that you tried other carbs and they did the same thing?

Are you running rubber line anywhere in line from the pump to the carb?
 
#15 ·
SHIP4BRAINS said:
It appears the stock primary jetting should be a 70 - secondary metering plate should be a 21 ( this i need to check ) pump discharge nozzle should be .031 ( need to check ) and the primary power valve should be 65 ( also need to verify.
Click to expand...
A #21 plate equates to #75 jets.

Therefore, your jetting seems to be close. I have found 70P and 76S thru #74P-80S (huge percentage 72P, 78S) to be right on for most very mild - mild big block engines with the 3310 series.
 
#16 ·
SHIP4BRAINS said:

Yes..rubber line from the fuel pump to the carb...
Click to expand...
Get a fuel psi adapter (only few dollars for rubber line install) and guage and check fuel psi.

80% chance you are running out of fuel or there is a piece of something that is intermittently blocking a passage.
 
#17 ·
cfm said:
A #21 plate equates to #75 jets.

Therefore, your jetting seems to be close. I have found 70P and 76S thru #74P-80S (huge percentage 72P, 78S) to be right on for most very mild - mild big block engines with the 3310 series.
Click to expand...
Yup, depending on the series of 3310, the 72P, 76S is the stock setup, with a primary and secondary PV. If you have a secondary plate instead of a metering body you might want to change that. If you want a completely setup 3310, I have many I would let go resonable.

But, It still sounds like your running out of fuel and not going lean.
 
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born2burn
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