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#26 |
Registered User
Join Date: Jan 2019
Location: St Peters, MO
Posts: 438
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Re: Another carb help...
The mention that it will idle, but drop RPM when put in gear AND aftermarket GM HEI caught my attention. I had a very similar issue which was an aftermarket GM HEI that wound up causing my problem: Truck had an occasional backfire or load up when driving. It progressively got worse to where it would start OK, but would die when put into gear. It would idle and rev OK, but ran badly under a load, or when stopping at a stoplight. I had to put it in neutral a few times to keep it from dying at intersections. Later it would lean out and backfire after it warmed up and eventually would not restart when warm.
Replacing the GM HEI coil and module with Davis Unified Ignition parts did the trick. No issues since June 2021. Coil and module are relatively cheap & easy to replace if you at least want to eliminate them as a possible culprit. Also, I compared a stock HEI module out with a Davis module - what a difference in performance, especially acceleration.
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1967 C20, 350 SBC w/Comp roller cam, 700R4 w/3.42 posi, PS, 4-wheel PDB, Old Air AC & GM Tilt column. |
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#27 | |
Registered User
Join Date: Apr 2022
Location: Moorpark, CA
Posts: 748
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Re: Another carb help...
Quote:
Set your base back to around 8-10 without VA and the vac port on carb plugged. Then with VA connected to the manifold vac port on carb adjust idle RPM as needed if you don't have it you can download owners manual for the 1406. and yes again it will say to use the timed vac port....its an emission thing, don't do it. It will however have all the tune and trouble shooting steps if you need them. I am assuming your timing marks are right and the carb otherwise is in good working condition, To me, your issue was and is no VA at idle because you used the timed vac port. |
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