Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem

Weird stuttering and high rpms

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Zach:
I am gonna say it is a timing issue, not sure if my timing marks are correct on the harmonic though. It runs significantly better when there is more timing 14-18 initial (factory) however my starter does not like it. 8 degrees initial is the absolute highest I can go in order for a smoothish crank on the starter. Currently in a decent spot but I know there is more power. I would run a high timing but I don't want to starter to constantly fail on me. The start issue only occurs when the engine is hot however. Maybe I can wrap it and see, don't have materials on hand for that at the moment though. Any ideas?

Cliff Ruggles:
Stock engine?

Verify that the mechanical spark advance is working correctly.  A stock 1977 400 4 speed engine is really LOW compression and would be fine with the stock timing setting.  "Bucking" the starter with more than 8 degrees initial timing tells me the balancer has slipped or the engine has a LOT more compression than it did stock.....

Zach:

--- Quote from: Cliff Ruggles on April 09, 2023, 01:37:55 AM ---Stock engine?

Verify that the mechanical spark advance is working correctly.  A stock 1977 400 4 speed engine is really LOW compression and would be fine with the stock timing setting.  "Bucking" the starter with more than 8 degrees initial timing tells me the balancer has slipped or the engine has a LOT more compression than it did stock.....

--- End quote ---

I think I am fighting heat soak. Starts fine on 18 but isn’t reliable when hot, going to wrap starter and exhaust and see where that gets me.. I quickly checked mech and made sure it moved a few weeks ago but nothing thorough, I’ll do that next. I also am gonna tests for Tdc and see where I am at on the harmonic because likely it has slipped. W72 has slightly more compression 8.2:1 I believe, still incredibly low but more significant than stock. I doubt the engine was ever hopped up. Thanks.

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