Edelbrock 750 cfm jetting advice...
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Cross-Country
Joined: Jul 2004
Posts: 57
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From: Spokane
Edelbrock 750 cfm jetting advice...
I just put an Edelbrock 750 w/electric choke on my newly rebuilt 390 that is cammed up a couple of steps and is estimated to have a CR of 8.5 to 1 - am I likely to need a jet and/or rod change with this set-up? It seems to run decent without any flat spots in acceleration, but only if my initial timing is set at about 14 degrees of advance (when I back it off to 10 degrees of advance, I have a minor stumble upon initial acceleration when the carb transitions from the idle circuit to the power circuit). Further info: I am running the stock heads with the Performer manifold.
Senior User
Joined: Aug 2003
Posts: 127
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From: Layton UT
Do you have the book that came with the carb? If not you can download from the Edelbrock website. That book will tell you how to adjust it and how to tell if it needs a rod/spring/jet change.
Although it sounds as though you don't need much tuning. A lot of guys run 390s set at about 12 deg advanced (me included)
So that may solve your problem. You didn't say wether it was pinging set at 14. You want it as advanced as much as possible without pinging. A longer duration cam and low compression should allow you to run at least 12 degrees advanced, probably more.
If you still have problems, post again on the FE engine forum - those guys are the experts and can set you straight
Dave
Although it sounds as though you don't need much tuning. A lot of guys run 390s set at about 12 deg advanced (me included)
So that may solve your problem. You didn't say wether it was pinging set at 14. You want it as advanced as much as possible without pinging. A longer duration cam and low compression should allow you to run at least 12 degrees advanced, probably more.
If you still have problems, post again on the FE engine forum - those guys are the experts and can set you straight
Dave
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Cross-Country
Joined: Jul 2004
Posts: 57
Likes: 4
From: Spokane
I do have the book that came with the carb, and will do some experimenting - I was just hoping to save some time...it is running good with no ping at 14 degrees of initial advance, so will probably only go rich one stage or merely change the step-up spring by one step...
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Joined: Sep 2001
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First of that carb is too big for the application which explains the stumble. You can probably tune it out by adjusting the accelerator pump shot. If the accelerator pump does not do it the carb is very much too big. Don't mess with the jets for this problem. That big carb will never give you a nice crisp off idle throttle response. Trade it to someone needing a carb for a 460 and get a 600 cfm unit.
BTW- your transition is from the idle circuit to the main jets. The power circuit does not come in until you hit real low vacuum. Of course you might be getting there just for the wrong reasons.
BTW- your transition is from the idle circuit to the main jets. The power circuit does not come in until you hit real low vacuum. Of course you might be getting there just for the wrong reasons.
