Thread: How do I change jets in a Holley 750 Double Pumper???

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Good Morning Everyone ... How do I change the jets in my 750 Double Pumper??? I went to the Holley web site but didn't see any info on this. hummm, this reminds me! I ordered a Holley Carb Book from Barnes & Noble weeks ago & haven't heard from them r/e; 'that my book is in'.... Do I need to wait for this book or is it no big deal to do this??? THANKS Bill.....

it is no big deal , take the 4 screws holding the fuel bowl on , ( that will be where your fuel lines are attached ya know ), remove the bowls, then remove the metering plate , there are dowel pins on the metering plate , you must remove it carefully and straight off, (the 4 screws hold both on with gaskets on both sides of the metering with a total of 3 gaskets ) your jets will be at the bottom of the metering plate, use a large screwdriver to remove and replace , do the same thing for the other side of the carb, that is about it ........

Take extra care that you don't overtighten the four screws when you put it back together. The carb body is easily warped, causing fuel to flow where it ain't supposed to. The surface is easily filed flat again, but it's better if it stays flat to begin with.

Put a red rag down under the float bowl.
Place a cleaned out small tuna can under one of the screws.
Drain the gas out of the float bowl into the tuna can then do what the guys have said.
(Helps to put a light pinch in one side of the tuna car which makes a nice pouring spout.)

What has led you to a jet change?

Imo, you'd be better off with a vacuum secondary Holley on a street runner.
Or a 750 Edelbrock/Carter if you like those.

I don't want to get into an Edelbrock/Carter vs Holley war here, they're all good carbs and I would not hesitate to use any of them - and have done so as well as I still own all three brands.

Main thing with any of them is try to get an unmolested one - new would be preferred.
All of them come jetted abut 5% rich for the expected engine size they'll be used on.
Nice part about that is, you can get the car running and drive it while you work any other bugs out and then start the fine tuning bit.

Fwiw, The Carter and Edelbrock both come off the Weber assembly line and are the same carb.

I know that a lot of guys run Holley double pumpers on the street and do ok.
By the same token I see a lot of cars at the strip running double pumpers and they'd do better with a vacuum secondary Holley, but . . . since that ain't Official Hot Rod Drag Racing Stuff they stick with their ill-running double pumpers....

Here's a pic of your metering block and bowl. First remove the fuel line to make it easier. You may have to get new gaskets. OEM's have a tendency to stick and tear. Follow the previouly mentioned catch can as you remove the bowl screws. It will pour out on the manifold as it drains.

....THANKS for the replys & pic's; Krizziee, R Pope, C9X, Nitrowarrior & Denny..... I'm going to order some jets & try it.

C9x, I'm going to change jets because my motor still runs to rich {I say "still" because the idle was set to rich before I adjusted it a bunch leaner. It's set 1/2 turn out on both sides}. I looked over my dyno sheets & noticed when they went from 70/82 jets to 71/83 that the HP went down {-3} as did the TQ {-.3 & peak 200 RPM's higher}. When they went bigger yet on the jets the HP & TQ went down even more. The 71/83 jets were the last dyno run & we were out of time so I guess that's why they didn't switch back to the smaller jets. So I figured I would switch back to the 70/82 jets. The plugs still show the motor running rich but not nearly as rich as before I leaned out the idle. Do you agree with me doing this??? Will it make that big of a difference in so far as leaning out the motor??? Oh, and THANKS for keeping an 'eye' on me & asking why I was changing jets!!! Oh I don't know what any of this means but there is some other dyno info I can give you; FHp Hp, ME%, FB 1b/hr, BSFC 1b/Hphr, CAT & WAT....
Yes, I've considered going to a different carb. I was thinking the Barry Grant 3 x 2 set up. One thing that's keeping me from this is I want more power from my motor & was considering a motor change. I don't want to put on a $2000+ carb set up & then still want to switch motors! The carb I have was on this motor 12 years ago & when I just recently had the motor rebuilt I also had the carb gone thru at The Carb Shop in LA. I told then to set it up for HP& not worry about gas mileage. MISTAKE!!! The motor puts out 20 HP more
than before but gets 5 MPG less than it did in a car that was heavier!

Denny, You have a good memory! yes, the power valve is what I need to adjust to take car of my car stumbling upon initial acceleration!!!

THANKS again everyone!!! Bill