The Stovebolt Site Forums The Shop Area The HiPo Shop 350/5.7L 1992 block / backfiring

hiya folks.

My 350 carbureted engine in my '65 C10 is backfiring. As in, I'm on the highway for awhile, when I let off to slow down for some reason, like to get off at a ramp when it drops from 65-70 to around 45 or so it goes KABOOM...

Yesterday I swapped out the spark plugs and put new wires on, seems to run better but it still back fired.

Anyway, looking for reasons why a engine backfires, more things to check. This is not something I have come across before in my automotive adventures so thanks for any information.

-Woog



This was all in there when I bought it, as things have broken I've had to figure out what year is what.

details:

Engine: 5.7 L Chevrolet — truck / 1992 / 350cid / 210 hp / manual trans / RPO# L-05 / TBI(throttle body injection) vin K(Canada assembly plant)

The distributor is 1985-1987 style, based on when I had to replace the engine module under the cap the last time... that's what it worked out as...

Carburetor: Holley — Model 4160 — single pumper 600cfm.

Intake: Edelbrock Standard Performer — Dual Plane

exhaust is stock type cast iron exhaust manifolds, from there the exhaust was rebuilt at a shop about 2 years ago.

Check the wiring in the distributor for chafing. As the vacuum advance moves, it may short out. If it's shorting out, killing the spark, it may come back alive as vacuum drops and fire a spark plug with the intake valve open.
We used to turn the key off and back on when rolling down the road in our Model A's to generate a backfire to get the girls to look back in high school.

Carbon buildup in head?

I'm with Kevin on this one. It sounds like an ignition issue. Do you have a tach? I would watch the tach and see if it drops to zero as in like the ignition is dead and then pops back when the kaboom takes place. (The Model A trick is/was one of the best. Those mufflers were tough.)

SimS

Two more easy quick things, check ignition timing and then check for vacuum leaks. Make sure no vacuum lines off or broken, you can also (with caution) take a propane torch and with the engine running direct the unlit torch around the intake, base of the throttle body or carb along with all other areas leaks could develop. If the engine speeds up you've found you leak.

Good Luck,
RonR

Thanks for all of the replies folks.

-Woog