Help on noise please

F

frederic

Senior Member
Iam very new to the flathead motor. I have a 59ab with alum heads, alum intake with holley 4 barrel, been hearing a light popping noise and rough running on acceleration and some times at idel, started to investigate what might be wrong. Did compression check, 155 +/- all cyl. Adjusted carb, thinking its fuel related, and replaced many parts on it. ignition is as it was when running well (electronic), wires all good. Tightened down bolts, nuts, hoses for vacuum leaks, OK. Vacuum gauge shows very very slight flutter. Will run well for a short period then start popping again. Isolated problem to rear cyl. drivers side (removing plug wire while idle and no change in rpm). Popping sounds mechanical to me. VALVE SPRING ???? Will a valve spring "climb/rotate" and work well for a period of time then let go and then re position itself in a sort of cycle?

Any help would be appreciated, Thanks guys.

Frederic
 
very rare but i have had a bad cam lobe do the same . is more on an excel then anything else, if cam has an issue. could also be a sticky valves too.
 
check valve clerance if it,runs ok when cold then starts poping when hot it could be clearance is to tight as the valve heats it expands also guide could be tight . take the intake manfold off it,s no big deal & check
 
I did not look at the psi or kpa when i looked at it. i was looking for consistent readings. Will take off intake and check clearance but i was under the impression one could not adjust flat head valves. I assume these are original style.

thanks
 
Frederic, With the aluminum heads, were they checked for piston to head clearance? You may have a piston touching the head. I know that doesn't account for the rough running but may for the mechanical noise. You may even a valve sticking or both of the above.
 
I know this may seem remote, but install a new plu in that cylinder and see what happens. Maybe the plug is fouled and not fully burning the gas.
 
frederic, Sounds like you could have a few sticky valves. this is normal with this new gas. Get a quart of Marvel Mystery Oil and drizzle some down all the throatle plate holes while it is running keeping your hand on the throatle to keep it running. Use about a 3rd of the bottle, put the rest in the gas tank and drive it about 10 or 12 miles and see how it acts. You need to put about a pint in the gas tank every other time you fill up or the valves will stick. G.M.
 
fREDERICK Checking a cylinder by pulling a plug wire off can cause damage to electronic ignition components .You can use a plug wire that is pulled off and attach it to a plug touching the motor no problem.A plug wire pulled off and not touching a ground (motor or frame) can cause the coil to break down and more likely with electronic ignition because of the higher voltage. Just a word of caution Lee34
 
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