Intermittent "puff Puff" At Exhaust

1956 CJ5, F134, 6v... Some background... Over the past 4-5 months I haven't been able to drive the CJ5 much but during that time I've done a bit to the rig including rewiring the entire thing (w/Walcks NOS type harness), installing a Pertronix 6v electronic ignition module (and manually adjusting the timing a tad to accommodate it) and troubleshooting a fuel pump issue that eventually lead to an NOS fuel pump install the other day.

Now that I'm ready to enjoy the jeep, I have an intermittent "puff puff" at the exhaust. A friend and old jeep expert thinks that the "puff puff" may be indicative of the engine needing a valve adjustment. He's 1000 miles away so I've been running things by him via video and phone. Because he's been "right on" with these long distance diagnosis in the past, I assume he's right in this instance as well BUT I wanted to see if there's anything else I should try before physically diving into the valves. I just put 9 gallons of fresh no-ethanol fuel and a bottle of Heet in the fuel tank to get out any condensation/water from the rig sitting over the past 4 months and freshen up the existing no-ehtanol gas. I'm not big on additives, but is there something else I should try in the oil or fuel if it is a slightly stuck valve?

For what it's worth, after adding the fuel and Heet I drove the jeep for about 10 miles the other night and didn't notice any hesitation while accelerating or stuttering while cruising at any speed, but the "puff puff" is still there...

 

Agreed, if it is pronounced.

OTH, my f-heads seem to have a regular heart-beat puff-puff that is harmless.

 

here's what the "puff puff" sounds like (added to original post as well):

 

thanks for the advice! had to increase the timing a little (went by ear) for the Pertronix, but I will dial it back a bit (rotating dizzy slightly clockwise) towards 5 BTDC tomorrow when I can get back into the garage. will adjust the idle speed first.

 

Will do, in that order - thanks!

 

Scare up a 4X6 note card hold it in two fingers along one end then move it over the exhaust pipe as the engine is running. To act like a damper. If it is sucked up tight against the end of the tail pipe at all (will be like a slap just for an instant) you have a Valve or more either out of adjustment or burned. Either way the card slapping against the end of the Tube denotes a Valve problem. Old School way to check valves when buying a used car. You could also connect a Vacuum gauge to the port on the intake manifold and then google a Vacuum Gauge chart to see what thats telling you. timing should be done with a timing light.

 

Vacuum gauge is the best bang for the diagnosis buck going, but almost no one thinks to use one.

 

Will a 3x5 card work???

 

Never heard the card trick before - will do that tomorrow as well. Thanks guys!!

 

Mine had similar issue. Motor would stall out around 35 mph. PO had timing way to advanced.

Also setting the valves was easy and made a huge difference.

 

Yes a 3x5 will work I'm just a 4x6 kind of guy LOL. As to the Vacuum gauge they will show a lot more then just a vacuum leak. Google up a Vacuum gauge chart and take a read.

 

I hooked up the timing light and tried to adjust the timing but I could not get the mark on the pulley to come anywhere close to the indicator on the engine without it stalling out. Mark on pulley is about an inch in front of engine indicator for 5° BTDC. With this in mind, I adjusted the idle screw as well as the fuel/air screw on the carburetor. I also used my stethoscope and can find no differences in engine sound no matter where I scope it. I need to do the rear Main seal at a local shop (I don’t have the capacity in my garage) so may wait on diving into valves until then.

This is what it is sounding like now at the exhaust . Much better but still the occasional “puff puff”.

 

A significantly burnt-out valve would be much more regular. Maybe it's running rich, occasionally combusting in the exhaust pipe??