Hi Doc,
I can't understand why I didn’t chip in earlier.
I had a problem on the Knight, very similar to that you describe but sometimes in a shorter distance if I used more throttle.
When the bike's performance dropped off I would stop, remove both side panels (rear head has left plug), remove both plugs and swap them. Reassemble the side panels, fire up and ride on to the next occurrence.
This went on for an extended period, changing coils and other ignition components to try to pinpoint the fault. Eventually I decided that greater level of strip down was required. For better access to the carbs I removed the seat and tank.
To lift the tank I decided to drain it and put a can under the main feed pipe. The initial flow soon dwindled and adding the reserve flow was no improvement. Removing the pipes from the triumph style lever taps, probably bought about 2010, didn’t give any more flow but when a tap was removed plenty of petrol became available. I found that I could poke a throttle cable through the tap but when it was removed couldn’t see through the tap.
In retrospect all the clues were there. I always used the front tickler so knew there was petrol there for initial starts. The bike would purr along until prolonged increased throttle for overtaking, hill climbing or motorway driving caused the “ignition” failure. The ignition was failing to burn the air in the engine that was intended to be a petrol air mixture.
Stopping to swap the plugs allowed the seeping petrol to refill the the carbs. Opening the throttle quickly drained the float chambers such that the bike appeared to choke up.
Changing the taps for modern ball valves with the stainless ball seated in nylon cured the problem as would reverting to original cork sealed taps as the problem was deterioration of the rubber seals in the modern taps being softened by the ethanol in pump fuel.
