Beginning last December, my engine was developing a slight hesitation just off idle. I'd step on the gas pedal and I would get a dead spot for a fraction of a second then recover, almost like a POP! but in reverse. The engine ran really smooth in any gear at anything over 1,500 rpm and sounded great. This season, the hesitation was getting more frequent, so I suspected the coil.
After I cleaned up all the electrical connections and swapped coils, nothing really changed much, and if I lugged it a bit in 4'th on a slight uphill it would do it repeatedly but randomly. Not like it was the same cylinder all the time, but it seemed to be jumping around. What was especially concerning was taking off out of an uphill stop and it was like it coughed once, bogged and then took off and that's not good!
So far, I have:
- Pulled the carbs and, on the bench, pulled the jets and shot some carb cleaner through them and then blasted in from the mixture screw holes - No real change.
- Installed new gaskets at the carb base AND at the intake manifold base - No change
- Checked the sync on both carbs and they were dead synced - No change
This morning, just on a hunch, I stopped at my FLAP store and bought a new set of NGK BR6HS spark plugs for $20 bucks (that's the plug Pat Downs recommends). Gapped them at .025" as recommended by Bentley (actually, they come pre-gapped) and put them in (which sounds easy, but this is a CMC where it's a real PITA to even see/feel, let alone get to, #1 & #3 ).
Miracle of miracles!!! It was the Twenty Dollar Cure! All of the hesitation is gone!! It was actually a pleasure driving around on back roads at slow speeds, again! Amazing what a new set of plugs can do.
Then I checked the gap on the old plugs, which had been in there since when I ran the MagnaSpark I, back when I had the big, clunky, MagnaSpark I HEI coil and they were gapped at .032" because IIRC, CB recommended that gap with their old coil. But now I'm running a new, more-or-less-stock, NGK coil which isn't as "hot" as the old MS I coil, so the .032 gap was just a bit too much for it and it was running as if it needed a tune-up.
So, the lesson learned is the plug gap should be matched to the voltage output of the coil and maybe checked so often - It makes a BIG difference!
Now just watch.... Now that I've written about it, it will probably screw up again, just to spite me.