The Stovebolt Site Forums The Shop Area Engine Shop Backfired hard - now runs like crap

I have been using my 52 4400 dumptruck to move dirt in my back yard and on about my 10th trip into the back 40, the 216 backfired hard through the carburetor and then began to run poorly. I popped the hood and noted that the vacuum advance hose was no longer connected at the carburetor. I hooked it back up and it immediately idled better, but still pops / backfires at higher revs and not enough power to back up the hill to dump the load. I babied it around to the shop and parked it. What do you suppose happened? I am going to check ignition to make sure it didn't initiate the first big backfire and subsequent problems, and carburetor is next. It has a Carter YF carb on it. Is this stock for a 52 216? I thought Rochesters were stock for these rigs. :confused:

I bet the timing gear slipped a tooth. This would especially happen pulling a big load.

Ken, any possibility that the force of the backfire may have damaged the vacuum advance mechanism in addition to blowing the hose off? Just a thought-checkin' stuff like that is free! Just hook up a vacuum pump and see if it will move the diaphragm in the advance mechanism as it should.

Wannabe

Hook a vacuum guage to the engine and run the engine.
It should have a steady reading at about 17 to 21 on the guage.
Look in manual to see sample readings indicating valve,timing or other problems.

I agree this sounds more like the timeing chain has sliped .
I am not sure what carb was used on your model. but on my 37 with a 216 it has a Carter W1 on it

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37 Chevy 1/2 Ton

As far as I know, the Carters were last used on '49s and from '50 on up they were Rochester B's.

And we've also learned that in 52 some of the trucks were built with parts from earlier models due to wartime shortages.

Ken,
Have you looked in the distributer cap for signs of arcing? I had a similar experience where, when the arc happened, two cylinders fired at once. Unfortunately, one was on the exhaust stroke and I guess the residual fuel was enough to completely shred the exhaust system in the ensuing explosion. I got the truck running again, but until I replaced the distributer cap it ran like it was a candidate for the junk pile.

My vote is timing. Check it with a light and see what you got.

The fact that you saw the vacuum advance line disconnected from the distributor would lead me to suspect the advance springs/ mechanism in the distributor. On the other hand it may have been the major backfire that blew the vacuum line off the advance & was caused by an entirely different problem.

I would check the cap and wires for cross firing. Was it damp out, high humidity? Check the cap for carbon trails from one terminal to the next. If there was enough humidity in the cap, the arc will burn the carbon out of the water and form a track. It will look just like a pencil mark.

On the timing chain, why would it jump a tooth under a load? The camshaft doesn't know the engine is working hard. High rpm it could jump, but would it just jump one tooth? Any more than one, would the engine run at all?

A valve could of hung up and caused it to back fire? Do you hear anything from the carburator or out the exhaust pipe? Can you pull one plug wire at a time with engine running and make it better or worse?

I have allways heard of timing chains jumping a tooth but never seen one do it. I have seen nylon teeth break off but never a chain break or jump. I have seen some very loose ones that should of jumped. Its just one of them stories I here about but never see . Joe