Some words of wisdom from Greybeard,
Quote:

A really cheap neon type timing light will tell you if it is in the electrics. Hook it up , tape bungee or somehow place the light so you can see it, and take a look when the engine starts missing. If you still have a nice steady flash and the brightness doesn’t change, the spark is fine. If it gets a little brighter, the sparkplug is shorting or fouling. Try this on both sides because Triumph uses 2 coils.

If it’s a fuel flow problem, the bike will run fine until the carbs run low on fuel, and it will run fine again for a while if you slow way down, coast or stop long enough for the float bowls to refill. When it first starts having problems, a little bit of choke will usually help for a while.

Symptoms of a sick coil will vary. If the insulation is breaking down when the coil gets hot, you will be able to see it right away with the timing light trick I described earlier. Same thing if the high voltage wire is breaking down and arcing to ground.
If the coil is delivering a weak spark, you can spot that by putting the wire on a sparkplug that is lying loose on the engine so that it is decently grounded. Crank the engine over and watch the spark. Especially with the reduced voltage from cranking the starter, a weak coil will deliver a puny yellowish spark.
Symptoms of a weak spark are pretty consistant. At higher speeds, the iron core of the coil will have less time to reach magnetic saturation between sparks, so the spark will get weaker with speed. Also, a poor spark has a harder time jumping the plug gap through a more dense mixture. So, wide throttle openings under a heavy load will cause the spark to miss. Back in the old days when they actually cleaned and tested spark plugs, the test was to hook it up to a coil connected to a 60 Hz source. The plug was screwed into a pressure chamber and the pressure was increased to about 150 - 160 PSI to see if the plug would still spark under pressure. Yes, that’s roughly equal to around 10.5:1 - 11:1 compression.
In the case of a failing coil or other ignition problem, the symptoms will be tied to operating conditions and/or temperature. If it is fuel flow, it will be tied to running time/fuel usage.

Also, that valve thing in the tank vent line seems to be a 1 way or maybe 1 1/2 way valve. It is there to keep vapors from escaping when the tank warms up,and the bike isn’t running and let air in as fuel is used. The 1/2 part is that it may have a pressure relief mode that will vent the tank if the pressure builds up too high. Since I have the CA vapor recovery system, I don’t have one to play with. It is worth the little time it takes to yank the thing to see if your problems go away, because they have been known to stick.



Blowing gravel off rural roads