Engine Back Fired In Carburetor – Timing Chain Broken?

engine backfired under the hoodMy question is, is there an easy way to decide if a 1974 F250 390 motor needs a new timing chain or not?

I’ve replaced the battery, battery cables, solenoid, spark plugs, wires, distributor cap, and starter. All it does if backfire through the carburetor. If you turn the distributor cap in any direction, it dies. Can you please help me?



Hi there Jennifer

Sounds like you do have a timing issue with the backfire problem. This could be due to the firing order be wrong…i.e. the wrong spark plug wire on the incorrect spark plug or pole piece on the distributor cap. I would start with TRIPLE checking the firing order and spark plug wire installation.

You can check the timing chain for slack, to see if the chain is worn out causing the problem but I kinda have a feeling if the engine starts and runs its more of a firing order problem or a problem with the valve train inside the cylinder heads.

A broken valve spring, bent push rod, collapsed lifter or some kind of valve problem can cause the same problems. If the firing order is ok, I would check the engine compression, if the engine is not worn out and low on compression I would probably pull the valve covers off and look at the valves.

Please share this with your friends,

Austin Davis

Posted in: Won't Start Issues

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