Question should I have vacuum to the vacuum advance at idle? I've got a slight exhaust popping that goes away if plug / disconnect the line. Pulled the carb and I wonder if I'm missing a plug in the bottom of the carb
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Re: 3721 SB carb 65 300 horse 4 sp
Yes, you should have full vacuum to the advance unit at idle. There is not supposed to be a plug in the hole you pointed out. -
Re: 3721 SB carb 65 300 horse 4 sp
No plug in the hole as Jim pointed out. That hole allows manifold vacuum to the vacuum advance control PLUS allows manifold vacuum to the choke pull off piston. It's the small hole on the passenger side of the carburetor so if it's open it's possible that when vacuum is it's highest like during deceleration, air will be pulled into the manifold and a lean mixture will result causing a pop.Comment
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Re: 3721 SB carb 65 300 horse 4 sp
Bubba strikes again! What is the number on the VAC?
DukeComment
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Re: 3721 SB carb 65 300 horse 4 sp
Thank you all for your responses. I've made a couple of carb / timing adjustments in preparation for PV and the slight exhaust popping has been a challenge to eliminate. I am used to seeing ported vacuum, not full at idle.Comment
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Re: 3721 SB carb 65 300 horse 4 sp
John, You didn't say which vacuum can you have. Your car originally came with a #238 can which gives far too much advance and needs to be changed to one that will work correctly. There's a reason GM used it for only one year and then threw that idea in the trash.Comment
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Re: 3721 SB carb 65 300 horse 4 sp
Jim,
It is a 236 and was recently replaced from Long Island Corvette. My old one wasn't working great.Comment
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Re: 3721 SB carb 65 300 horse 4 sp
A 236 is waaaaaaaaaaay too aggressive for a 327/300. It's only functionally correct application is small blocks with mechanical lifter cams.
See the following thread:
There are plenty of used 201 15s out there which would be "correct" (both functionally and from a judging perspective) for your car if March or later production, and even if you get an OE replacement B22 the deduction will be minimum.
The VAC is worth three points - two for originality and one for condition.
I'll also add that some "reproduction" VACs may have the "correct" number stamped on them, but don't come anywhere near OE performance spec, and in any event a 236 is not correct for your engine - either functionally or for Flight judging.
This simple ten dollar part is very important to achieving good driving characteristics and fuel economy, but few understand what it does and how to select a functionally correct VAC. A B22 is functionally correct for a base camshaft engine with manuals trans, but a B26 is best for Powerglides.
DukeComment
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