Thread: Aluminum metering blocks

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I thought you guys might want to see this.
The 1st pic shows a typical aluminum metering block alongside the traditional block, note where teh idle circuit gets its' supply - esp the one at about 4oclock on the metering block.
That notch cut in for the idles crossover is overly large and will intersect with the ported vacuum supply on a carb that has vacuum.
The 2nd pic shows a normal gasket with tombstone shaped pv cutout, if you look at the impression of the idle crossover you can see it extends into the vacuum port.
The 3rd pic shows a normal metering block gasket (with tombstone cutout) laying in place, if you look closely at the vacuum port hole at about 10oclock there is a shadow - it is the idle crossover. The 4th pic shows a pick inserted right into the idle crossover from that vacuum port.
What happens is taht fuels dribbles into teh engine thru the baseplate via the vacuum hole, you can't see it.
They make a special gasket for the aluminum metering block, it has a round hole for the power valve and does not have the hole for the vacuum as the carbs they are designed for do not have vacuum advance for distributors.
For carbs that have vacuum advance ports - pic 5 - i show how i isolate the idle crossover with a piece of aluminum duct tape. The idle crossover works fine and is just isloted from the vacuum port.
I see a ton of these, folks just have this overrich idle and blame it on all kinds of things. Lots of times you can pick up demons etc that will be cut loose because they can't get it to idle right.
I discovered this years ago with my 2bbl circle track carbs, i have since checked every aluminum metering lock and they are all the same - just the color is different.

OJH: Thanks for the tip. I have a 302 that has a MSD billet distributor, without vacuum advance, and a 670 Holley Street Avenger. I have a "rich idle" problem that I put off to the "radical cam" the engine has. You may have given me a good solution: thanks for sharing!

Hate to give you false encouragement, that carb don't have the aluminum meterin block unless somebody has 'fixed it up'.