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Old 06-12-2018, 09:55 AM   #21
scicala
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Default Re: 8BA or 8CM and Holley 390 cfm vs other combinations

If your distributor has a vacuum advance on it, try hooking it to manifold vacuum instead of ported on the side of the carb. Then need to adjust the idle spped back down to desired speed and re-adjust the two mixture screws for best vacuum. If it's already that way, try to hook the dist diaphragm to ported vacuum and readjust idle speed/mixture.
Might be worth a try and costs nothing but about 15 minutes of time.


Sal
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Old 06-12-2018, 11:21 AM   #22
tubman
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Default Re: 8BA or 8CM and Holley 390 cfm vs other combinations

Sal's method is worth a try; I know the guys on the Corvette board are always talking about how it helps. Most of the carbs they use are just a 390's bigger cousin.
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Old 06-12-2018, 11:21 AM   #23
Kahuna
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Default Re: 8BA or 8CM and Holley 390 cfm vs other combinations

Scott
I had a similar problem on a Holley carb that drove me nuts.
My friend came over and opened the idle mixture screws 1/2 turn
& the problem went away, never to return.
Just a thought
Jim
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Old 06-12-2018, 01:23 PM   #24
scicala
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Default Re: 8BA or 8CM and Holley 390 cfm vs other combinations

I'm assuming the idle mixture screws have been adjusted for best idle already. If not, that may very well be the issue as Kahuna stated.


Sal
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Old 06-12-2018, 02:19 PM   #25
Modelacoupe3
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Default Re: 8BA or 8CM and Holley 390 cfm vs other combinations

Update: upon disassembly and inspection of the float bowls, I found what appears to be left over metal in the accelerator pump passage. It looks as if the passage was not deburred after the drilling process.
I also found the accelerator pump housing screws were on the loose side, although it did not leak. I’ll correct the found issues and report back with the results. See the attached picture, upper right portion of the float bowl.
Thank you all for your responses.
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