Edelbrock 750

Discussion in 'The Mixing shop.' started by Mach5racing, Apr 24, 2019.

  1. Mach5racing

    Mach5racing Well-Known Member

    without getting into the Qjet vs other carb debate I have a edelbrock 1407 750 carb with electric choke and vacuum secondaries. I have searched all over the internets for info on jetting. I was wondering if anyone had the same carb and any jet size info for for me. I have installed a fuel pressure regulator. The car has a poston S divider with a 1” spaced, TA long tube headers to a 2.5” exhaust with h pipe. Upgraded distributor and coil. I have been having a little trouble getting it tuned right and I was just looking for some info and suggestions on getting my current set up to work correctly. Thank you, this web site truly is a great wealth of knowledge for us Buick owner.
     
  2. jaye

    jaye Well-Known Member

    are you running an electric fuel pump?
     
  3. Mach5racing

    Mach5racing Well-Known Member

    Forgot to add it’s a stock mechanical pump
     
  4. CSC5150

    CSC5150 New Member

    What engine is this on and are you running HEI?
     
  5. Bens99gtp

    Bens99gtp Well-Known Member

    you said getting it tuned right.......can you explain a little what's going on, when and under what condition. that should be a nice carb depending on motor combo. I ran mine into the 11 seconds on my 455
     
  6. Mach5racing

    Mach5racing Well-Known Member

    It’s non hei and it’s a Buick 350. Well it is surging while cruising. And not accelerating like I think it should. For sure it is running lean. I pulled a plug and it’s definitely lean. The carb was freshly rebuilt and has 104 and 101 jets that came with it in it now which I think are too small. My plan was jet it to what the carb would have came with from edelbrock and go from there but I hoped someone had a similar setup and could guide me in the right direction.
     
  7. wkillgs

    wkillgs Gold Level Contributor

  8. Mach5racing

    Mach5racing Well-Known Member

    I did see all that but that is for the 1407 carb not on any specific engine. That’s why I was wondering if anyone had luck tuning the 1407 edelbrock carb on a Buick 350. Just looking for some real world advice. Thank you
     
  9. Bens99gtp

    Bens99gtp Well-Known Member

    best to start as edelbrock had it, the graph work well on my 455 but I had to be between 2 or 3 stages richer for power, my was race so all I cared about was idle and wide open. might take some tinkering
    stumbling on acceleration might need more accelerator pump shot but moving the hole in the pump arm
     
  10. Mach5racing

    Mach5racing Well-Known Member

    Thank you for the advice. I will change the jets to what it would be on a stock edelbrock 750 and go from there. I will post what I find out Incase this helps someone else out in the future.
     
  11. wkillgs

    wkillgs Gold Level Contributor

    Stock cam? good vacuum?
    Best method to tune is to get a wide band Air/fuel ratio gauge. Select main and secondary jets for best WOT numbers, then change metering rods and springs to get the part throttle tuned in.
    It's tough to read spark plugs with modern fuels since they don't color like leaded gas did. But there are some useful guides out there.
    You can try smaller diameter metering rods to see they will richen it up enough to eliminate the surging. They're easier to change then the jets. I'd try that first.
     
  12. CSC5150

    CSC5150 New Member

    I’m running an Edelbrock 1812 on my ‘70 455. Out of the box it runs great. Just had to set idle mixture and idle. I agree though, start with the base calibration for the 1407 and keep us posted!
     
  13. Mach5racing

    Mach5racing Well-Known Member

    Stock cam and very good vacuum. I will get into it tomorrow and see what I find. And csc5150 I do know that since your Buick is sitting next to mine in the garage haha
     
  14. DEADMANSCURVE

    DEADMANSCURVE my first word : truck

    yes the upper pump arm hole will give you the most aggressive shot , I usually use the center hole as a start up point . make sure the jetting is correct - and bigger jets in primary , check the metering rod numbers in case someone went wacko there , pump nozzle should be a 31 or 35 , the 750's take a different part# pump assembly than the 600's . if not using one edelbrock recommends a thin metal spacer kit under a square bore carb on a dual pattern intake to avoid possible vac leaks . check the round plugs pressed into the rear ( facing out ) of the boosters , I've had a couple that were loose that I epoxied . edit - just rebuilding a 800 AVS carb , same plug/epoxy problem again . emailed edelbrock . that shouldn't happen .
     
    Last edited: Apr 28, 2019
  15. telriv

    telriv Well-Known Member

    Jetting between electric choke & manual choke 750's are different with the electric choke being more lean all the way around with metering rods & jets. Timing being too far advanced will ALSO cause surging at speed/cruise. Could be the limiter bushings for the mechanical & vacuum advance are missing on one or both.

    Tom T.
     
  16. Mach5racing

    Mach5racing Well-Known Member

    Thank you for the help. I had to work late today so as long as I don’t have to work late tomorrow I’ll get a good look at it
     
  17. Mach5racing

    Mach5racing Well-Known Member

    I changed the primary to a 113 and the secondary to a 107. It made a big difference. I don’t have the 71-47 metering rod which would be stock on the 1407, the calibration kit didn’t come with it. I have a 73-47 with pink springs in there instead and it seems to be pretty good. Pump nozzle was a 35. I am going to do a little test driving and see how it is. I may need to adjust the metering rods and springs but hopefully that’s it. Thank you for al the help so far.
     
  18. Mach5racing

    Mach5racing Well-Known Member

    It is running better for sure. The surging seems to be gone. It does smell a little rich as well. Cruising felt good. Wot from a stand still would make it bog and die. So I still have some more tuning to do but it’s getting there. And accelerator pump arm is in the center hole.
     
  19. 1972Mach1

    1972Mach1 Just some guy.....

    The thing I've learned, especially with an AFB, is to get one step cleaned up at a time. As in: Get it to idle properly. Then get your tip in right. Then your primaries. And so on. Some circuits overlap each other, so the transitions cover two different things, but only do one thing at a time if you can help it. You can hide issues with one circuit by fudging another, but it's just a crutch. With your good vacuum signal, it should be fairly easy to get it right. Find a loop to drive that's a few miles long and drive it. Then change one thing and drive the same loop. It might take a few hours or a day, but you'll get it running properly. Edelbrocks run pretty decent on just about anything, but they're kind of a finicky carb to get just right, but when they work well they're great.
     
  20. Mach5racing

    Mach5racing Well-Known Member

    Awesome advice. Thank you. I’m hoping do do that this weekend and get it set.
     
    1972Mach1 likes this.

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