Holley Tuning Question
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Holley Tuning Question

  1. #1
    AIR POWER TAPPED OUT's Avatar
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    Question Holley Tuning Question

    I have a 850dp on my 455 olds (rebuilt carb, rebuilt motor). The motor runs good and the spark plugs read right on after running it but when I get into the throttle wide open it has a bog to it, but if I let off and hammer it again it picks up with no bog. I have changed out the secondary jets to larger ones to try to solve teh problem but no luck. I dont know if I need larger discharge nozels or what? Any Advice would be appricated.

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    Senior Member GT Jets's Avatar
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    Sounds to me like undersized accellerator pumps, did it ever run right under hard accel?, there are pump cams, nozzles, bigger pump bellows, someone on here has a proven recipe...

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    AIR POWER TAPPED OUT's Avatar
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    No it never did run right on hard eceleration and wot. If anyone has a good setup that I can try for my carb let me know.

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    Senior Member Widetrack's Avatar
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    850 DP set with 80 pri. with 6.5 PV, 87 sec. 40 CS front and rear no air horn! How does this compare with what you have already?


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    What size accel pumps are in it?

    My Holley runs the small on the primary and the large pump on the seccondary. Has always worked perfectly this way.
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    There is supposed to be a small needle under the squirter screw, if its not there, or its stuck, or it doesnt seat correctly it can cause your problem. Remove the squirter, and see if there is fuel right up to the top of the boss, if not then SLOWLY move the pump arm and see if fuel comes to the top. If it does, see how long it takes for the fuel to go back down, it shouldn't go down at all. These needles wear and get corroded and don't seal. The first pump squirt must refill the passage from the fuel bowl level to the squirter, the second quick shot gets all of the normal squirt before the passage can empty. TIMINATOR
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    AIR POWER TAPPED OUT's Avatar
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    Well apparently my Holley isn't a 850 I checked the list numer and it's a 4780-2 which makes it a 800. I checked the little needles under the squirters and the rear one was stuck and I had to tap it out. I cleaned the needle up a little and it doesn't stick no more but that doesn't mean it's no good. I have 76 primary jets/6.5 PV, 88 secondary jets, and both front and rear squirters are 31.Any thing else I need to check out or replace??

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    Tapped Out I assume that your timing is correct. If the changes you made to your carb did not solve the problem , I'd also check the manifold vacumn numbers on your new motor. You may need to finish the tune with a power valve change. The transition circuit may coming on be a bit late. For example, if your motor is making 14 " of vacumn at idle you may want to try an 8.5 PV. If you still have a problem I'd look at the fuel pressure during the W.O.T stumble. Good luck. Jim

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    Sit N' Spin Jetaholic's Avatar
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    Quote Originally Posted by Performance Jet View Post
    Tapped Out I assume that your timing is correct. If the changes you made to your carb did not solve the problem , I'd also check the manifold vacumn numbers on your new motor. You may need to finish the tune with a power valve change. The transition circuit may coming on be a bit late. For example, if your motor is making 14 " of vacumn at idle you may want to try an 8.5 PV. If you still have a problem I'd look at the fuel pressure during the W.O.T stumble. Good luck. Jim
    Good to see ya posting here Jim.



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    AIR POWER TAPPED OUT's Avatar
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    This carb has the 30cc prim. and 50cc sec. accelerator pumps. I think I have narrowed the problem down to the stuck needle under the squirters. Does anyone know if the numbers for my squirters sound correct?

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    Sit N' Spin Jetaholic's Avatar
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    Yes, your carb came stock with 0.031" squirters in both the primary and the secondary.



    Quote Originally Posted by HammerDown
    Kendall L-427 Super Blu...extreme-pressure (ep) lithium complex keeps my thrusting balls happy
    Quote Originally Posted by back2k5 View Post
    Well I am putting in a nice stereo system in the Carrera...maybe Ill put on some rap and turn the scoop sideways

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    Cas
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    Quote Originally Posted by TAPPED OUT View Post
    This carb has the 30cc prim. and 50cc sec. accelerator pumps. I think I have narrowed the problem down to the stuck needle under the squirters. Does anyone know if the numbers for my squirters sound correct?
    here's a link to the Holley Carb Numerical Listing to give you all the factory specs on Holley carbs.
    http://www.holley.com/data/TechServi...%20Listing.pdf

    it can be a little confusing when you first look at it. The way it works is the odd number pages as they come up have the list numbers of the carbs and some info. The even numbered pages are a continuation of the info of each carb along the corresponding line.
    For example, your carb is on page 5 line 5. The rest of the info is on page 6 line 5. Hope it helps

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    Cas
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    here's one that's a little easier to read-
    http://www.usmotors.cz/old/tech_tips/HolleyCarbList.pdf

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    I had an 850dp on a 454 in my jet. It took 42 squirters to take out the bog.

    Tim

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