[Grumman72]

Hello All!
I have a 72 Grumman RV w/454 BB, purchased 3 years back has been running great However, i noticed at times it would POP back through carb. After some checks, vac/intake leaks, new bosch plat plugs, excel wires & dist.
I removed 750 cfm carb & replaced gaskets to be certain I had no leaks & noticed the rear barrel on RH side had a decent amount of black residue, the others had none.
I now am wondering if the issue is in the valve train of the RH bank?

Any suggestions or does this sound plausible?

[SWHEATON]

If its a steady poping sound(esp when under a load like wheen accelorating) it could be a cam lobe/s going flat.

When a cam goes bad you will get a poping sound through the intake and there were plenty of bad cams in SBC & BBC in the early 70's to go around. I know this 1st hand from working on cars & replacing many bad cams in BBC & SBC over the past 35 yrs. This is esp true when the motor runs hot like pulling a heavy camper in your case and where the engine compartment is tight & hotter than you would find in std car engine compartment.

The best way to check for a bad cam is to warm the motor up,pull the valve covers,and start it up to see if all the rockers/valves are going up/down approx the same amount.

Note:take some small pieces of AL foil and press/form them over the upper ends of the rockers to keep oil from squirting out of the rockers making a mess.

If they are great,if any are not traveling the same distance a cam lobe or lobes is going flat or has gone completely flat.

In that case you would need a new cam lifters.

If you need a new cam send me your email address through T/C and i send you some good info on proceedures to follow to help avoid wiping out a new cam durring breakin which i see hapening from time to time here on T/C.

FYI,a compression test will not always show a worn cam because it depends on if the lobe is completly gone and if its the intake or exhaust lobe thats bad so keep that in mind.

Let us know how you make out.

Scott

[Grumman72]

Thanks Scott-
I was going to remove valve cover this evening & check springs. That should be an easy check while I'm there.

[Grumman72]

Cured: #2 intake rocker retaining nut had backed off.


I enjoyed reading all the other posts, I like the site!

[SWHEATON]

Well the rocker stud backing off is nice problem to find,easy to fix and costs nothing,you lucked out.

Scott