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11-10-2019, 01:33 AM | #1 |
Senior Member
Join Date: Apr 2015
Posts: 158
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spark knock under load
Crab distributor with pertronix and correct coil. Vacuum brake hooked up to manifold vacuum. Edelbrock slingshot intake with dual 97's. Edelbrock heads... 6 volt pos ground/
Runs good, maybe a bit rich but knocks under load/hard acceleration. New to all this. What should I be looking for or try? |
11-10-2019, 04:42 AM | #2 |
Senior Member
Join Date: May 2010
Location: Solihull, England.
Posts: 8,749
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Re: spark knock under load
Knock the timing back a little. Was it ever timed with a light? Do you have a timing mark?
The timing adjuster is on the usa drivers side of the distributor and would need to be loosened and moved upwards to back the timing off a little. (Known as retarding the timing) Mart. |
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11-10-2019, 10:30 AM | #3 |
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Join Date: Apr 2015
Posts: 158
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Re: spark knock under load
No. Never timed with a light. No mark for TDC. Thought I had read somewhere to not hook up the vacuum brake but I cannot find that again, so wondering if those with the pertronix hook up vacuum to it or not?
I will try to rotate distributor up a mark or two and see what happens. |
11-10-2019, 06:31 PM | #4 |
Member Emeritus
Join Date: Nov 2012
Location: Wichita KS
Posts: 16,132
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Re: spark knock under load
I think you want the vacuum brake hooked up. Bubba claims to see a difference in the stability on a scope. The vacuum brake was originally for help with ignition ping, it slows the rate of advance I believe.
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11-10-2019, 11:39 PM | #5 |
Senior Member
Join Date: Apr 2015
Posts: 158
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Re: spark knock under load
On thehamb someone suggested to try adjusting the vacuum brake by turning in ash bolt 1/2 turn at a time.
Thinking of trying that first as idles good. Can’t test drive till ties though. |
11-11-2019, 09:09 AM | #6 |
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Join Date: May 2010
Location: Oshkosh, Wi
Posts: 4,526
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Re: spark knock under load
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