Motor issue

Asked by Jul 20, 2017 at 04:37 PM about the 1985 Chevrolet C/K 10

Question type: Maintenance & Repair

305 sbc motor backfires like crazy while running.
We were trying to start it and after we were done
trying, the motor jumped and the crank went in
reverse. I assume it has to do with timing. How do I
fix this?

2 Answers


Timing was the first thing that came to mind. You have to find someone with a timing light who knows how to use it. He would be an old guy like me. The leads of the light are attached to the spark plug of the #1 cylinder and the battery. Aiming the strobe light at the marks on the flywheel (and there's a stationary pointer) with motor idling and vacuum advance disconnected and plugged off, you loosen and rotate the distributor a few degrees each way until you have a spark advance of about 6-10 degrees. As a temporary remedy you can rotate the distributor a little without a timing light to see if it helps. I would say go clockwise first. Also, if this engine has breaker points set them to 0.020 inches first as this will affect the timing. Adjusting points first might be the only thing you need to do. Replace condenser next, check the distributor cap then check plugs wires for cracks. Sounds difficult but it is really easy.


I recommend replacing the points and condenser with a uniset assembly, popping back or backfire while running is a classic condenser failure, then proceed with the rest of the Dwell and Timing checks.

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