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Engine ignition timing issue

  #1  
Old 02-13-2019, 12:02 AM
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Default Engine ignition timing issue

I've built 4 truck engines, and the mods have not been extensive.
8.5/1 compression, a small cam (204deg at .050" presently) 4bbl carb and headers.
But something has always had me puzzled, and that is that my engine seems to idle best with about 45deg of ignition timing. And that is way out of the ballpark.
I have triple checked my timing marks against TDC on the firing stroke of the #1 cyl - And maybe I should check again, because this creates some very unusual issues with my spark curve.
It's also possible that there's an issue with my timing light.
I'm just trying to figure this out.
It's been this way on every engine that I've built. And the commonality is that I have used the same balance marks on the same harmonic balancer and the same timing light as well.
Does anyone else notice that their engine idles best at 45 degrees advance?

Thanks
 

Last edited by BK87S10; 02-13-2019 at 10:01 PM.
  #2  
Old 02-13-2019, 04:56 AM
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Been awhile since I messed with anything you could adjust the timing on, but is the vacuum advance included in the 45?

If that's all initial timing, it's gonna pre detonate like crazy under any load. Usually 10-12 initial, and then more with vacuum at idle
 
  #3  
Old 02-13-2019, 10:08 PM
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I should make it clear that this is a carbed engine with vac advance dist.
I have it on full manifold vacuum. If I remove the vac advance hose the engine runs terrible.
I've been trying to remember when I first began seeing this.... I don't use my timing light often since HEI came out , which was a while ago.
It was this way on the last engine I built - And when I built this one, I made sure that the #1 was at TDC when the pointer was at 0
Maybe I have been repeatedly been screwing up when dropping the dist in
It barely runs at 10 - 12 deg -It chugs and shudders and then dies

This is obviously not normal. I need to figure out where I'm going wrong.
My old engine was this way too, but I just ran it by setting the dist where it seemed smooth and then backed it off if it detonated, and it seemed OK
 

Last edited by BK87S10; 02-13-2019 at 10:15 PM.
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Old 02-14-2019, 12:18 AM
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[QUOTE
It's been this way on every engine that I've built. And the commonality is that I have used the same balance marks on the same harmonic balancer and the same timing light as well[/QUOTE]
Try a new harmonic ballancer Or at least compare with a new one to see if outer ring has slipped and rotated from factory position in the rubber.
If this has happened you will never be able to set base timing right.
 

Last edited by odat; 02-14-2019 at 12:33 AM.
  #5  
Old 02-14-2019, 10:33 AM
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Yeah - I'll be checking to be sure that the timing marks align at TDC... Again - Just to be certain.
But what I'm starting to think is that my MSD ignition is causing an error in my timing light

 
  #6  
Old 02-14-2019, 11:37 AM
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Originally Posted by BK87S10 View Post
Yeah - I'll be checking to be sure that the timing marks align at TDC... Again - Just to be certain.
But what I'm starting to think is that my MSD ignition is causing an error in my timing light
MSD is a waste of money but doubtful if the ignition is causing it - But how ever you stated that you have full vacuum to the vacuum advance, so when it's hooked up yes it will move timing way off scale.
 
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