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I have a holley 670, it has 2 metering blocks. The front has idle mixture screws on either side, however the back has none. From Holley's store picture, it means that this setup is wrong. The holes don't look threaded. So I'm assuming this explains my bad vacuum? Not really sure why it is setup this way. Any idea why someone would do this?
From: At my Bar drinking and wrenching in Lafayette Colorado
The Holley 670 is not a 4-corner idle mixture screw carb. Like most standard Holleys, it's a 2-corner idle carb. The secondary block does not have mixture screws. It has no effect on your engine vacuum. Check your timing...
Lars
From: At my Bar drinking and wrenching in Lafayette Colorado
As a note, just because it does not have idle mixture screws on the secondary side does not mean that it doesn't discharge idle fuel on the secondary side: There is an idle fuel crossover passage in the throttle plate, feeding idle fuel from the primary side over to the secondary side. For this reason, it is important that you balance out the primary and the secondary idle throttle openings so the carb is "leaking" the same amount of idle air on both ends of the carb to mix with the fuel being discharged at both ends. This is the purpose of the secondary idle speed screw located under your throttle plate. Use this to make sure that the primary side throttle plates do not have an idle speed setting more than .020" of transition slot exposure in the throttle bore.
Holley 670
