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This one has me very confused. Built the engine years ago. 289 bored out, stock pistons, afr 165 heads, comp cams xe268h, weiand stealth, holley 670 street avenger, ignitor 3 module, headers etc.

The issue I'm finding is I can not get the engine to run right with 12-18 degrees of base timing. I have verified tdc and verified it is at tdc on the harmonic balancer.

When I run the engine and pull maximum vacuum, it runs great but it's showing 55-60 degrees of base timing.

I am using a stock replacement balancer and have my timing pointer installed. The engine runs perfectly with this timing.

Thoughts on why the timing is showing so advanced? There's no possible way it's true and accurate. Yes that's with the distributor hose blocked and no I don't have any vacuum leaks.
 

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With the changes you've done to the engine, etc. I wouldn't plan on using the "stock" timing marks. If the centrifugal advance weights are still in your distributor, they can advance your spark by 15-20*. If your balancer isn't new, the outer ring might have moved on the hub. If it runs great at the timing you're reading, I'd say not to worry.
 

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I had a similar problem after replacing the intake manifold. Would only with timing up near 50. Pulled and redid the manifold and all was good. Apparently I had a big vacuum leak somewhere
 
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