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Old 06-13-2012, 06:02 PM
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Timing jumping on timing light

I have 350 sbc afr heads 280xfi cam hei distributor 24 initial 12 mech 36 total and 3k total is 36 the timing light is steady if i rev it higher it starts advancing by itself
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Old 06-13-2012, 06:24 PM
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Quote:
Originally Posted by prettyboyced
I have 350 sbc afr heads 280xfi cam hei distributor 24 initial 12 mech 36 total and 3k total is 36 the timing light is steady if i rev it higher it starts advancing by itself
Just because you see 36 degrees at 3000 rpm doesn't necessarily mean there is no more mechanical advance left. You can check for this by revving the engine higher to see where the advance stops, or put weaker spring(s) on the mechanical advance just as a test to see how much advance the mechanical really has.

Another thing is if the vacuum advance is hooked up, disconnect it and plug the hose to the carb so you are only seeing initial and mechanical timing w/the timing light.
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Old 06-14-2012, 11:07 AM
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also to add, alot of times when guys fix the advance curve so the distributer has no advance at all {fix or lock timing} when you put a light on it, you will still see the timing jump up and down a bit.. thats due to the play or gap between the cam gear and distributer gear with the oil being slushed between the gears.. that play in the gear mesh causes a bit of timing jump up and down.. When you see this kinda timing jump, judge by the highest point on the timing to determine where to set it at even when running engine at 3000 rpm to set totall advance or what ever rpm you choose..
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Old 06-14-2012, 04:57 PM
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Make sure the distributor is tight sometimes you will think they are but when you rev the engine it will move around enough to through things off and jump around. JMO What type hold down do you have on the distributor anyway ?



Cole
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Old 06-14-2012, 05:34 PM
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Im going to put in a simpler opinion:

How good is the timing light? And are you using a multi spark system? Some older or cheaper lights dont work at high rpm and many dont work at all with multi spark setups. Typically at higher rpm they jump all over the place simply because the multispark throws them off. Try a better light?
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Old 06-14-2012, 07:20 PM
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Is a snap on timing light I have no multispark just hei but the clamp is tight it's a stock top hold down clamp
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Old 06-15-2012, 03:37 PM
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Quote:
Originally Posted by prettyboyced
Is a snap on timing light I have no multispark just hei but the clamp is tight it's a stock top hold down clamp
Is just the stock HEI ?


Cole
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Old 06-15-2012, 09:29 PM
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Yes stock hei
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Old 06-16-2012, 09:57 AM
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Quote:
Originally Posted by prettyboyced
Yes stock hei
Take a sharpie and put a line from the TDC line on the outer ring down across the rubber section to the inner damper hub. When you hit it w/a timing light this will show you if the damper outer ring has become delaminated from the inner hub, causing the timing mark to jump around.

You can run the line from the outer ring to the pulley if need be- the pulley is bolted to the inner hub.

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Old 06-16-2012, 12:47 PM
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HEI Bearings

If your HEI isn't new, pull it and check for play in the bearings.
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Old 06-16-2012, 12:50 PM
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Never mind.

Disregard my last post......I must have misread the original post. Sorry.
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Old 06-17-2012, 12:50 AM
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I go tthe same damn problem, only mines terrible at idle,
literally jumps about 8 degrees or so
Ive been told its the timing chain play..but Im not 100% sure about that
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Old 06-18-2012, 10:38 PM
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With drawing a line from the outer ring to the inner what am I looking for
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Old 06-18-2012, 10:41 PM
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I tried timing again with timing light and to get 36 total I have to bring initial to 30 and I tried driving it like that but it started to mis at a steady cruise
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