Valve train noise ? missing/backfires now on acceleration

First stroke is ring seal.. initial buildup to about 75% plus of the 5 stroke total indicates good ring seal.

This depends on the location of the piston at the start of the test, and why you test every cylinder twice, to come up with repeatable results. it's assumed that the piston won't stop in the same position twice.

JW

 

Can I be dim witted here and ask if this could be as simple as carbon on a valve and the noise and misfire are from the sticking valve? I guess I would dumping some Berrymans in the carb to see if something was carboned up? Regardless, the thread is interesting, look forward to hearing the resolution.

 

I would bet it's the cam. We flattened some of the lobes on my son's first 350 and it did exactly what you are saying. Pull both valve covers and coil wire, then have someone crank over the engine a few times while you watch the valvetrain. I'm guessing you are going to find at least a few rockers barely moving. In our case we did not get the break in procedure done right because we had a few problems that we had to shut the motor down for. It was gradual and took about a year before it was really bad. Have you been using oil with plenty of zinc in it?

Ken

 

Replace the hei module,.....just went thru this

 

Fast and free way to rule out failing cam is pull valve cover and measure lobe lift of the suspected offending cylinder.