AFB carburetor - stepup spring shimming?

1073 Views 2 Replies 2 Participants Last post by 1987cp, May 14, 2009

1987cp

Discussion Starter · May 14, 2009

A few weeks back I read a book about tuning Edelbrock and Carter carburetors. It noted that while the heaviest stepup or fuel enrichment springs available are rated at 8 inches Hg (the silver springs from the 1486 and 1487 tuning kits), it is possible to shim the springs so that enrichment occurs at 10 inches Hg or higher. Has anyone here done this, and maybe has some tips on how to do it?

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HIVOLTJ

· #2 · May 14, 2009

1987cp said:
A few weeks back I read a book about tuning Edelbrock and Carter carburetors. It noted that while the heaviest stepup or fuel enrichment springs available are rated at 8 inches Hg (the silver springs from the 1486 and 1487 tuning kits), it is possible to shim the springs so that enrichment occurs at 10 inches Hg or higher. Has anyone here done this, and maybe has some tips on how to do it?

I don't know if you'll find much help here, I think almost all of us carb guys run some kind of Holley. You would have to use something that would still allow the vacuum past (like a small washer or something).

I don't see why you would need to lean it out that much, is there something else that needs fixed??

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1987cp

Discussion Starter · #3 · May 14, 2009

Actually, the idea is to richen the mixture a touch sooner - with an effectively heavier spring, the metering rods will move to the "power mode metering" position somewhat earlier into the throttle travel. This particular combo is currently pulling smoothly at WOT, but it has an annoying stumble that I'm pretty sure is just before the rods move up at 8 inches of vacuum. I do still need to locate my vacuum gauge so I can have a better idea of just when it's stumbling, though.

So far I've been unsuccessful in locating a vacuum leak or ignition problem .... and since the stumble is now all but gone after going 3 "stages" rich on the "cruise mode" metering ....

I like the thought about using a washer, I'll have to see if I have anything that'll work. If not, Ace Hardware is about a half-mile away.

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