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Old 11-09-2008, 04:09 PM
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exhaust question

Probably fuel related though. 327-350, 4-sp. Had the car on the chassis dyno, full day, dialed in very good. Later on, I replaced the open spacer to a four hole. Motor liked it. Car runs excellent, but between gears, say shifting between 4500-6000, get a brief crackle out the exhaust. Like unburnt fuel. Float levels good. Didn't seem to matter if I used ported or full vacuum for vac. adv. canister. This is on my 64 vette. Also have very slight surge, at around 2500, but seems to be more noticeable when in 3rd gear. Ignition is all MSD. I don't think they have adjustable vac. adv. canisters. Could surge also be caused by a lean condition in the idle transition circuit?

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Old 11-10-2008, 04:53 AM
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Off idle surges are usually caused by too lean a mixture so move up 2 jet sizes. Or they can be caused by the power valve. I never realized this until I had one that surged constantly and it drove me nuts, no matter what I did I couldn`t seem to get it out, then some of the guys on here told me to change the power valve back to the stock unit that came in the carb, so I did and jetted it up 2 sizes no more surge. What was causing the power valve surge was at cruise it would be running along fine then I`d hit a hill and it would go to surging due to the engine load activating the power valve due to the vacuum change.
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Old 11-10-2008, 05:45 AM
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So when you put the original power valve back in, did you go back to a 6.5, I assume, from whatever you had? Do you consider 2500 rpm to be off idle? I know it is off idle, but thats quite a bit off idle. I thought an improper vacuum advance canister can also cause surge.
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