Odd “knocking” noise at high RPM while WOT

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letgomyleghoe

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Hi,
I’m brand new to the forum so apologies in advance if this is in the wrong place. I recently replaced my stock intake and carb on my 1974 c10 350 with an edelbrock air gap rpm and 1406 combo I got off Craigslist. The factory smog pump system and manifolds are still on the truck, which is my next project. After swapping the intake and carb I notice this odd grinding/knocking noise, I only hear it about a second before the shift at WOT, never during normal driving. I thought it may be my lifters so I set the preload on those to no avail, been messing around with timing as well, which seemed to help for the first pull, but promptly started again on the next. I’m honestly stumped at this point, hoping it’s not rod knock or a ground off cam lobe, any other suggestions or ideas would be appreciated.

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85K304SPD

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What did you set your timing at? Initial or total.
 

Catbox

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been messing around with timing as well, which seemed to help for the first pull, but promptly started again on the next.

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Did you tighten the distributor hold down before the test after fooling with the timing?
That one has gotten us a time or four....
 

Matt69olds

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When in doubt, cut the oil filter open. If there is internal issues, you will see the shrapnel in the filter long before you hear anything.

If the filter is clean, safe to say it’s not a disaster problem. What’s the total timing, and does the vacuum advance make a difference?
 

letgomyleghoe

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Did you tighten the distributor hold down before the test after fooling with the timing?
That one has gotten us a time or four....
I gave it the good and tight, not sure the exact torque.
 

letgomyleghoe

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What did you set your timing at? Initial or total.
I looked this morning before work, initial timing with vac advance off is at 14* btdc, didn’t have time to mess with it much, gonna try and set it to maybe 10 or 12 and see how it runs.
 

letgomyleghoe

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When in doubt, cut the oil filter open. If there is internal issues, you will see the shrapnel in the filter long before you hear anything.

If the filter is clean, safe to say it’s not a disaster problem. What’s the total timing, and does the vacuum advance make a difference?
I don’t have a light for total timing, gonna get one and check tonight. I’m guessing this is my issue as I only experience the issue at WOT high rpm with likely 0 or near 0 vacuum.
 

85K304SPD

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Set it at 8 or 10 initial and you should be good. Try each one and see how it feels and sounds. No need for an advance "total" timing light.
 

PrairieDrifter

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Sounds like just barely too much timing. I would say about 10-11 initial. Definitely should check total too.
 

Old Guy Bill

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A vacuum gauge can be helpful if you’re not sure about the timing also.
 

letgomyleghoe

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So I figured it out, had the distributor connected to manifold vacuum which would add about 20* of timing at idle. With the extreme advance at idle I could only get it to run right at idle or while driving, connected it to ported vacuum set the timing to about 12 and it runs great now with no detonation.
 

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