TOPIC:

A little premature perhaps, but after 18 months of running very well, suddenly I have cylinder 2 not performing. Not a blip! Just running on five all the time.

I say 'performing' because at work I took the plug out and it is definitely getting spark, and cylinder one is fine, so it is getting fuel and presumably air too....

So what can be wrong here? Dropped valve? 

I will do a compression test at home this evening, but in the meantime any ideas?

Going to the Harpenden Show this afternoon.... then home, some 40 miles. Will I b*gger up the engine running on five for so long - at low revs of course?

Paul

 "......and cylinder one is fine, so it is getting fuel and presumably air too...."
"So what can be wrong here? Dropped valve?"
 
Don't go off the deep-end just yet !
A "dropped valve" would have destroyed that cylinder......and you'd know it !
Getting air ?   Certainly, but not necessarily fuel.   Your #2 Main-jet (which feeds the pilot-jet) and or Pilot-jet is likely blocked.
Riding it as it is?   Nope ! 

I Agree with Scotch. If it was a tight valve there would be backfiring or popping back through the carburetor. It could be a shorted sparkplug or as Scotch has suggested a plugged main jet on the #2 side of the carburetor.
In either case, no riding until you get it figured out.

Thanks gents!

Well, I had to ride home (20 miles at 2000 rpm max) and that went without a hitch, on five, with not a single bop from no2 and no other strange noises from the engine.

Just measured the compression and ALL cylinders are between 110 and 130 so there is compression. I swapped over spark plug no 2 with no 6 and started her up. Seems OK now and all exhaust pipes went hot, but as it is late I won't test ride until tomorrow.

I hope somehow I have sorted the issue (wishful thinking!) as I really don't want to take the carbs off as it is a royal pain to put the air box back on, but if it needs it, I will do it. If it is a jet issue, both will probably be blocked and if the carbs are off I may as well check all of them. 

... oh deep joy, can't wait!

Paul

P.s. never heard of a shorted plug! And ironically enough this is the plug that I had to replace a few weeks back as it had broken in two, so it is virtually new.
 

"Shorted Sparkplug"- Yes you've heard of it just not referred to as "shorted" A gas fouled plug or oil fouled plug or a carbon traced plug is a "shorted plug". The spark, rather than jumping across the gap,  finds an easier less resistant path to ground and runs down the center insulator to the ground of the plug. On rare occasions when the strength of the spark is not strong enough to ionize the air in the gap, the plug either misfires or doesn't fire at all. 2 strokes especially the Kawasaki triples oil fouled plugs and they were shorted. Replacing the plug and you were back in business. if you replaced the plug and still had a dead cylinder, this is another issue.

So I have to ask, How do you split a sparkplug in to two???

I'm sure KawBoy remembers two strokes 'loading up' with excessive fuel, then having to hold throttle WFO for minutes on end while the engine burbled and gagged on excess mixture until she 'cleaned' out and ran proper again.

I've broken the ceramic on hard to reach plugs when too lazy to step and fetch the proper tool..