If I had a nickel for every minute I’ve wasted chasing the elusive “white rabbit,” I’d be a wealthy man indeed! Three + weeks now shot troubleshooting what could’ve been such a simple fix. At first I thought, like carguy, it must be a carb issue (what with modern ethanol tainted fuel and all the related problems).
After a thorough inspection and simple cleaning/tuning/balancing, however, this was ruled out. I even checked and adjusted the timing, which was found to be waaaay advanced.
With little to no backfiring, good slow idle and only missing at higher revs. (Around 2000 or so under load), I was convinced it must be fuel causing the issue and began replacing the old hoses and blowing out the lines where I could and installed a filter prior to the carburetors, which was long overdue.
Not sure where/when Dad purchased this fuel pump I added 4 years ago, but I had a rebuild kit sent to me and found that the only parts I could use were the sump gasket and main diaphragm! The inlet/outlet valves in this repro. are pressed in and not held with the retaining clip. Reassembled with what I had and it seemed to deliver good pressure.
Still, the car continued misfiring under load and gradually worsened to where it barely idled.
I moved on to replace the coil (Old Lucas still registered good resistance), spark plug wires and finally - FINALLY - the capacitor/condenser. EUREKA!!! This simple - $3.00 - part, which I actually replaced 2 years ago was the cause of all my problems!
Had I done better research, I would have found the excellent troubleshooting procedures for this very issue in the Ignition Chapter of my Haynes Manual (For whatever reason, the HM is typically the last place I look!). It describes an embarrassingly simple test for capacitor failure, so don’t make the same mistake I made. Save yourself hours/days/weeks and possibly hundreds of dollars if your engine begins suddenly misfiring.
According to other sources, there has been a rash of faulty condensers/capacitors lately. I ordered this one (Intermotor Brand) from Engel Imports here in Kalamazoo, MI.
That, my friends, is a lengthy way to let y’all know that my problem has been solved!