so, I have a mostly stock 1957 and distributor on what is 292 or possible a 312. haven't be able to confirm which. That being said it has a summit M2008-MV8600 carb. (600 cfm). Seem to run ok on primary but when you step it down the secondaries seem slow and a sluggish response but pulls fairly well. Is the 600cfm carburetor to large? Is it pulling in too much air for the fuel ratio. I opened the carb. pri jet is one size smaller then the stock show. Secondary jet are Stock size. Any suggestions would be helpful. the jet size on 500 cfm carb. stock is Pri. 62 & Sec. 68, the 600cfm Pri. 68 & Sec. 73.. Summit suggested you could run to lean on fuel and air flow would be same. might harm motor. Thanks

Is this sluggishness a new problem?  Did anything change?
I don't know anything about that particular carburetor but I have a 600 CFM Holley on my 292 and it's not sluggish.  I would guess it's a jetting problem or an accelerator pump problem.  Have you removed any of the spark plugs?  On my Holley, larger accelerator pump discharge nozzles made it more responsive.   

You might check the spring in the vacuum diagram. If the primary jet has been changed (or shipped wrong, I’ve seen that happen) maybe the spring is off too. Other things will cause a bog like mention above, but a weak spring bringing the secondaries in early will do it for sure.

miker
55 bird, 32 cabrio F code
Kent, WA
Tucson, AZ

What's wrong with your 500 cfm carburetor?

Carb is less then 8 months old. I talked to summit about this, and they said should go with a heaver spring in diaphragm as is getting too much air. Others stated I should have got the 500-cfm version. This carb built like the old 4100 Ford cigar box carb made by Holey for summit.

I do not have the 500cfm carb. but should have got that instead of 600cfm some have suggested..

The 600 will work fine once you dial it in. That’s the good part about the vacuum secondaries that are easy to tune. I’ve gone too light on every thing from SU’s to Carters to Holley’s before l learned. Only ones I didn’t screw up were Quadrajets. Didn’t own one till after I learned.

miker
55 bird, 32 cabrio F code
Kent, WA
Tucson, AZ

I have good results with both the 600 and 750 cfm versions of the Summit carburetors on the Ford Y engines.  Being vacuum secondaries, the secondaries only open enough to meet demand meaning it’s difficult to over-carburate the engine.  While the 500 cfm versions are good daily drivers, they tend to be under sized for most Y engines with any kind of aftermarket camshaft and the better heads.

You do not mention if you purchased this carburetor new or it was acquired as a used version.  Be sure to double check the fuel levels as being too low can cause the issues you have.  Out of the box, the jetting is very close but if that carburetor has been acquired as a used version, then I would suggest putting the jetting back to the stock sizes and try again.  Ignition timing and how the distributor curve is set up will also be a player.

Lorena, Texas (South of Waco)

This carb built like the old 4100 Ford cigar box carb made by Holey for summit.

The CARB is not made by HOLLEY. It is a copy/knockoff of the HOLLEY 4010/4011 SERIES.

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i purchased it new from Summit.  I installed it last summer and work on tuning it in till winter hit.  Now that weather is getting better, I am start too think of how to dial it in better.  So figured i put it out there for those great people with helpful ideas. I not much of a carb. guy and get somewhat intimidated with messing it up. I don't know much about the internals of motor and stuff but appear to run and drive well i just noticed that when you step down it doesn't seem to respond well. It pulls with some hesitation until it seems to catch up. Maybe a quest like noy enough fuel or to much air. I dropped the pri nozzle size I believe to a 62 from 68 thinking that what the 500-cfm nozzle are. Maybe I should go back to original nozzle size as you suggested. Instead of looking at spring in diaphragm?