1973 850, Boyer MK III analog ignition, was running great on a highway trip, then all of a sudden it starts to run like crap. I was thinking fuel starvation on one side, had to keep feathering the throttle to keep it going while I limped home. LH cylinder was farting and coughing and backfiring, like a misfire. I let the bike cool, checked fuel flow, it is good to both carbs. Changed the fuel in tank for fresh premium gas. Checked for air leaks, nothing apparent, but changed float bowl gaskets anyway. Still runs bad, and RH header is HOT, with LH header just warm after running for a minute or two. Checked valve clearances, and they are all good. Reversed HT sparkplug wires LH to RH, and RH to LH, same symptoms, and still isolated to LH cylinder. Changed sparkplugs ( NGK BP7ES) with new. Next did a compression test, with engine cold both cylinders were at 90 PSI exactly, not the greatest but both cylinders equal, and pressure held. Charged up the 1 year old AGM battery, still no improvement. I have done a thorough going over the ignition wiring, all seems good with no loose connections. I have removed one sparkplug, grounded it, run the engine on the opposite cylinder (did this for both sides), and I am getting equal spark on both, or so it appears. Engine is definately running crappy on that LH cylinder. I have previously replaced the wires on the Boyer stator plate, and bike has run smooth since then, two years ago. I will check the magnet coils on that plate for continuity, see if there is a fault there, but failing that, I have run out of ideas.
Would the Zenier diode be a possiblity, and if so how would I check that?
I appreciate any suggestions...thanks
Would the Zenier diode be a possiblity, and if so how would I check that?
I appreciate any suggestions...thanks