Sorry about the long diatribe. Sound familiar anyone?
I Bought a 1982 XV920RJ two seasons ago. My XV has been acting "goofy" since pretty much day 1. On an extended trip to California last year, half way through Washington (in 80 degree heat) she started to run poorly. Basically felt like she was on one cylinder - no power below 3000 rpm, low idle, crapped out at stop lights. This behavior healed itself to some degree as it cooled towards the end of day one.
So I got home and began fiddling. Carbs off and cleaned. Plugs - caps - wires - coils are all new. Still when warm (Calif weather is very hard to simulate on Vancouver island) she crapped out. Ran it past the mechanics at Duncan MC and was presented with an interesting point. Both cyls were still running when the problem occurred, only one was at such low revs as to be indistinguishable until you set the idle up to 2500 or so and started her on first one, then the other cyl. Turned out the rear cyl was ticking WAY slower. "Air leak" the guy pronounced, and I skulked off home to fix it, lesson tucked away.  I had replaced the intake manifolds (inch long tubes the mixed air travels thru for .002 seconds before entering head) in the spring, and I was kicking myself for not getting a good seal. So I gooped them up with gasket goo and reassembled, fully expecting to be thrilled and relieved. Nope. Not a bit of change! Ack!
Next I set the idle screw up high, then started her on one, then the other cylinder, and used the carb balancer screw to adjust until each cyl was at about the same ticks. I have the screw backed all the way out and the front cyl is still about 100 - 200 revs low, but WAY closer than 1000 off like it was. I watched the plugs religiously to see if I was starving one cylinder, and so far as I can see, they both burn the same decent color of brown, no white or black.
Now the XV always starts well (if you can get past the sound of the starter grinding). It does not misbehave MUCH in hot weather. In August this year I traveled to Alberta, traveling through Idaho and Montana in very hot weather. Medicine Hat, my target, reached a record 39.3 the day I arrived. The bike ran flawlessly except she is still a little undependable at an idle. Idle speed drops a bit (and as I already have it low this spells Mayday at the odd light) and the power is just not there. Other than this, which is bearable, the biggest problem is she pops through the headers like you would not believe. If the clutch is engaged on any kind of down hill, she hammers like there is no tomorrow. A little embarrassing and anti-social. I am also concerned that eventually this might start blasting bits off the valves. This behavior is always present, regardless of temperature.
I have tested compression, put a meter on the pickup coils and what I can understand from the igniter. The carbs have been cleaned 3 times. I have done my "on-line" homework and found the same advice twice: These fellows are saying that if pretty much what I have going on is in evidence, change the igniter box. Unfortunately it is a $600 trick. I'm thinking of doing the exciter (pickup) coils as well so everything is new.
I have never in all my playing around checked "float level" in the
carbs, which I see as my next move. If the fuel level is ok, I'm still in ignition hell. What is it? Fuel? Electrical? Air?
All thought, stories appreciated. Thanks to the web master for providing this excellent site!
Steve Lovejoy
Cobble Hill, Vancouver Island, BC, Canada
lovejoy@cvnet.net

Check your valves and valve seats. You might have a cracked valve seat.
Harry Spruit