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Old 04-22-2013, 06:34 PM
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Tuning Holley 750 Double Pumper

Hey everybody I have a sbc 355 10.5-1 Compression, .535 .550 Roller Cam, gets pulled to about 6200. The car is a drag car only gets trailered to the track. I went with a Holley 750 Double Pumper I know many of you say its too much carb but a heard a lot of people saying and showing me a 750DP tuned right is great on any engine tuned right especially I tuned up 350 like mine on the track only.

I am going to be rebuilding it this week and was hoping someone could give me some general jet sizes to start out with and accelerator pump cam color to change too. I have the pink ones on both pumps which I heard are very aggressive and which is why my engine was bogging so much with it in.

So what would guys recommend I start with. Also do both accelerator pump cams have to match?

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Old 04-22-2013, 06:53 PM
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70-72 primary 80-84sec jets 4.5" pri power valve.. .031" shooters.
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Old 04-22-2013, 07:09 PM
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Both cams do not have to match. The best way to dial in the carb is pull the spark plugs and read them. If they are black and sooty, your way too rich. I'd start by dropping the jets by .02. In otherwords, if you have .072 jets, drop down to .070 and see how that runs. When you get close to a gray color on the plugs, then you can mess with the accelator cams, nozzle sizes, etc. to dial it in even more.
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Old 04-22-2013, 07:39 PM
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Quote:
Originally Posted by F-BIRD'88 View Post
70-72 primary 80-84sec jets 4.5" pri power valve.. .031" shooters.

Thank youuu! I just needed a a good base numbers to start with. Should I swap out the pink cam before I run it Friday? It was bogging pretty good off the line? I think pink is the 2nd most aggressive cam being a sbc 350 I figure I gotta tune it down a bit
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Old 04-22-2013, 08:34 PM
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explain how you get a bog? and the engine can use an 850 for racing,but 750 is also a great start.
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Old 04-22-2013, 09:18 PM
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explain how you get a bog? and the engine can use an 850 for racing,but 750 is also a great start.
well I have 4.10s and a 3500 stall converter. If it helps at all. But 0-3000 id say it ran great but when I give it throttle in neutral or in gear it just fell on its face id back off get into it again it would pick up and fall again. This was with me putiing to the floor on the 1/4 mile.

Id have to say running it to the staging lanes down the 1/4 and back to my spot I burned 2 gallons of fuel it was all over the air cleaner and stuff Id say the carb needs rebuilt for sure which ordered from holley. I figured that was most of my problem but I just wanna tune it right. Plugs were fouled from just one run too.
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Old 04-23-2013, 07:24 AM
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It sound to me you need extension tubes on the secondary jets. It could be getting exposed when get on the gas.
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Old 04-23-2013, 07:48 AM
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I run pink cams before and they should work just fine.....fuel all over the air cleaner? you above the vent tubes, or too close to them? does it launch that hard that fuel comes out the vents? Agree w the extensions on the rear jets, fronts should be under fuel w/o issue. float stickin?
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Old 04-23-2013, 03:18 PM
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fuel pressure, float setting, new needle seats,

Poor thorottle response is more of a ignition timing issue.
Racy cams need a lot of timing at idle. A stock timing curve will not work.
Lock out the mechanical advance system. Set the now locked fixed timing to 34-36deg BTDC.
Now reset the carb.
What camshaft?
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Old 04-23-2013, 07:17 PM
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a 750 is just fine, I have a 950 on a 362 cid ford. if you want to spend the money buy the external adjustable metering blocks so if you need a little more or a little less it just a turn of a screw, also get bowl extensions, plus you don't need the power valves.
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Old 04-23-2013, 07:33 PM
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Quote:
Originally Posted by F-BIRD'88 View Post
fuel pressure, float setting, new needle seats,


What camshaft?
Lunati

Advertised Duration (Int/Exh): 282/290
Duration @ .050 (Int/Exh): 231/239
Gross Valve Lift (Int/Exh): .535/.550
LSA/ICL: 110/106
Valve Lash (Int/Exh): Hyd/Hyd
RPM Range: 2400-6200

What all do you recommend for fuel preasure on my carb?
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Old 04-23-2013, 10:23 PM
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Holley carb. 7psi
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Old 04-25-2013, 01:32 PM
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Found the secondary powervalve had a block off power valve in its place. I put it back in since its only a drag car and don't need the fuel mpg. and I went with 70 jets in the primary, 80 jets in the secondarys I hope that was ok with the block of PV
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Old 04-25-2013, 03:10 PM
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The reason it was blocked on the secondary is when you smash the gas pedal it causes exposure in the opening in the PV as the gas is pushed back. And since the opening in the PV sits higher then the main jets the result is lean bog. I'm pretty sure why Holley stop using secondary PV for that reason.
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Old 04-28-2013, 08:58 PM
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Found out 1 and 8 were not firing on my cheap japo(KMJ) distributor. That explains the back fires and rich condition haha
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