Backfire

BIGLA

MEMBER
1974 CHEVROLET 1500
120 MILES

Hello 2CarPros,

I have a 1970 Chevrolet 1500 pickup truck and it is backfiring like a 105mm Howitzer artillery gun.

I can hear consistent loud explosions from the tail pipe. I have noticed that it has always had this intermittent timing drag or retarded-ness while turning the engine to start. But now the engine will start but it sounds like a bomb going off continuously scaring me and neighbors.

I am a Veteran who is on fixed income so I am forced to repair it myself and asking for your help to nail down my problem so that can I fix the problem.

Could it be the fuel pump or and the timing problem or both. A neighbor friend tells me it is timing problem but I am not sure.
Should I replace the fuel filter and the fuel pump along with a new vacuum hose along with new distributor cap and rotor? I just do not know

I know I am asking a lot of you and I really do appreciate you kindness and help.

1 Reply

ASEMASTER6371

MECHANIC
52,797 POSTS

Good afternoon,

First, thank you for your service. Hoorah

Anyway, it could be some of several things.

1. Cracked distributor cap. Carbon tracks will cause backfires.

2. Cross ignition wires. This is only if you had work done and they put the wires back incorrectly.

3. Broken rocker arm, push rod or cam shaft lobe worn out.

4. Yes, retarded timing could do it. Make sure the points are gaped at.018 or if you have a dwell meter, the swell should be 30 degrees. The timing should be about 6 degrees before top dead center.

Roy