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Old 05-24-2021, 10:29 AM   #6
geezer#99
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Join Date: Aug 2009
Location: Bowser
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Re: GMC 250 Inline 6 Tuneup

Plug off the vac advance on the distributor and set your initial timing at 10 degrees.
Your manual likely says the timing is lower but for diagnostics set it at 10.
Then hook the vac advance back up and let us know if it runs better.

Did you set the point gap with a feeler gauge?
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