The subject bike is a 1967 T-120R, restored by somebody (unknown to me) and with unknown miles since restoration (The speedo was broken when purchased). Conventional points ignition and AMAL Concentric
carbs are fitted. Recently purchased by me, the bike has several kinks to work out, but Ill start with the most alarming problem. After a few minutes of warming up, at about ¾ throttle under a mild load, one or both cylinders just quit. No coughing, missing, or sputtering, they just die. After a minute or so, I can get both cylinders back running and ride home. This has happened now five timers. The plugs after these run are a little sooted around the margins, but I think that richness is mainly in the idle circuit (another problem for later). The plugs also seem really hot, making me dread overheating, but I may be making this up.
Guys, I hope this rings a bell, and I need suggestions for a basic approach to it, i.e., what to check first versus second or third. I can tell you what seems okay: gas (new), air filters clean, plugs are new, points work and are properly gapped, alternator serving plenty of amps to the electrical system. The bike starts, idles fine and sounds fine when revved. I have not yet re-timed the engine (new TDC indicator is on the way), nor have I had time to adjust the valves. I havent looked into carb jetting because frankly, Im need to be convinced that carburation is really the problem before I get into re-jetting. Thoughts?