Spark plugs?

First, some background..... 1968 F-head, Pertronix ignitor, new cap, wires, and rotor, new NGK spark plugs (Champion J8C equivalent), MSD 6 Digital spark box and coil, K&N cone air filter in place of the oil bath unit.

Now for the problem....
intermittent misfire mostly off-idle - looked at the plugs - seems to be running rich, so I cleaned out the air filter - cleaned up the plugs, checked the wires for chafing (none). Checked for vacuum leaks - none, checked the carb baseplate -good. Restarted the Jeep, no change....
Anyone running a hotter spark plug? Is this a good idea? Any thoughts or suggestions??
Thanks
Chris

 

Are you running the Carter carb or a Solex? I ran the carter and could never get it to stop fouling plugs, tried a slighly hotter plug (forget the #) but didn't cure it. IIRC, plug heat ranges deal with heat transfer, not hotter spark. Swapped in a Solex and much better. I found a deal on the Solex so I never tried rebuilding the Carter. I'd check your timing too. Is this the same rig that had the trouble starting last winter??

 

Did you check for air leaks around the throttle shaft on the carb? Pretty common for old carbs to leak there and suck air. Spray some starting fluid or similar there, and see if the rpm's change.

 

:iagree: Basically the reason I didn't mess with the Carter.

 

Yup, same rig -
It has the military style carb - carter y-s.
The plugs and tailpipe are sooty and black.

 

Sprayed carb cleaner EVERYWHERE - no change in RPM at all.....