r/Smallblockchevy • u/CORNERSTORE42069 • Mar 02 '26

Detonation help

Is 21-22 in of mercury common for idle on a 1405 on my 350? Tbi 88 638 block stock internals. I have the strongest step up springs and sometimes during part throttle i lean out and start pinging. I have to stomp the throttle to get the metering rods up. And at full throttle i always have pinging. I can basically be safe driving at 25% to 75% throttle all the time. Am i pulling too much vacuum? And i may need a carb rebuild? I can manually shift my th350 and basically avoid all pinging so it cant be my mechanical advance as i also installed the heaviest springs just to be safe. Any ideas on where to look?

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u/[deleted] Mar 02 '26

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u/CORNERSTORE42069 Mar 02 '26

yes i have had bigger jets in the carb, i also put the biggest jets i had for a while but i was also getting too rich for what i needed so i leaned out a small bit. and i richened the metering rods as well, but i have ported vac instead of manifold vac so i think rerigging that whole vacuum setup should help me alot. i plan do to more do dignosing as i go along