Hi,
I'm having some problems with an Edelbrock 750cfm carb on a mild LG-4 305. Everybody tells me that this carb is too big for my engine. Since I can't afford to change it for a 600cfm, what are my options ? I have asked Edelbrock but their answers are too vague so I'm turning to your knowledge here.

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'85 SC 2.8 now Z28 Clone with 305 LG-3! 700R4, Edelbrock RPM, Hooker Headers, CompCams 212/218, and 750cfm Edelbrock Carb

 

Is it too big? Probably.

Is it gonna cause the world to end? Nah.

You and your motor can probably live with it just fine, only barely notice a difference.

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"American made baby. 100% American iron. The muscle among the masses. My hero. Yep, you can take your ergonomically designed, space age, computer controlled, 4 door, cup holding map lighted split double wishbone split fold down retractable cargo covered moon roof piece of transportation and keep it. For I have felt the thunder. And I know the difference!"
JSP Motorsports
ICON Motorsports

 

I really can't get to tune this carb right...Is there a way to reduce the flow ?I was thinking on going lean 12% on both pri and sec. Any suggestions ?

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'85 SC 2.8 now Z28 Clone with 305 LG-3! 700R4, Edelbrock RPM, Hooker Headers, CompCams 212/218, and 750cfm Edelbrock Carb

 

Oh, BTW, mileage was around 19 with non-cc Quedrajet and now i'm getting 15 ! If this can help ...

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'85 SC 2.8 now Z28 Clone with 305 LG-3! 700R4, Edelbrock RPM, Hooker Headers, CompCams 212/218, and 750cfm Edelbrock Carb

 

One of the reasons that the QJet gets such good mileage has nothing to do with it's flow rating. It has to do with the idle circuits. THey're almost always VERY lean. They were all emissions carbs from day one, don't forget.

Most aftermaket performance carbs are designed with idle circuits that are much richer than the average QJet. This helps them deal with big cubes, big cams, etc much better. It's always better to run a little rich than a little too lean on the idle circuits with a big cam, it makes the thing much more dirvable and the idle more stable. But it also kills fuel mileage!

Fixing this requires more than just leaning the idle mixture screws, it requires leaning the entire idle circuit. This usually requires drilling idle air bleeds a little larger (.005" or so). The danger is going too far, leaning out too much and junking the carb. Not for the novice.

What you CAN do without much trouble is to run the idle mixture screws as lean as possible while still maintaining an acceptable idle (lean them down until the engine strarts to stumble and them back them out just far enough to smooth theidle out). Also, jet the primaries down about 4 jet sizes from stock factory jetting. Compensate for this by jetting the secondaries 4 jet sizes richer (changes made to the secondaries have nothing to do with fuel mileage) This will often give you much of your mileage back. What it does to performance you may not like, however.


[This message has been edited by Damon (edited October 18, 2001).]

 

Thank you Damon, i'll get the calibration kit and fix that.

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'85 SC 2.8 now Z28 Clone with 305 LG-3! 700R4, Edelbrock RPM, Hooker Headers, CompCams 212/218, and 750cfm Edelbrock Carb

 

A 750 cfm Edelbrock or HOLLEY is absolutely too big for a 305,a 600 cfm would be more responsive and give better gas mileage, Better yet a properly tuned Q-jet[off a sbc]would make a better all-round street/perf. carb than either. I know I'll get those that disagree with me but ask anyone who has taken the time to set the Q-jet up right and they will confrim it!

 

It is much too big. Go to a 600 CFM and you will be much happier.

 

Ill trade you my 600 edelbrock for your 750. If its still shiny.
:-)