Motorcycle Repair: Yamaha XJ750, perth western australia, accellerator

Question
Hi Wayne
I have just purchased a 1986 Yamaha XJ750. It was used here in Western Australia by the state Police. The only problem I have is that it runs very rough. I removed all spark plugs and found that the plug from #1 cylynder was fouled with a black sooty residue (dry, not wet and oily). I cleaned and reset all plugs and reinstalled them but after only a few minutes of running, the same thing happened. I have tried new plugs etc and the same thing happens. I also noticed that the engine "races" at idle. The engine speed can go from 1000 rpm to around 3000 rpm without the accellerator being touched but will then settle down to aroound 1000 rpm again but all the time there is an intermittant miss in the firing. This is the indication that the plug in #1 cylinder is fouled again. Can you offer any assistance please.
Regards
Jason E. Cole
Perth, Western Australia

Answer
Jason,

-first thing I would check is compression psi
on that fouling cylinder. It may have
built up alot of carbon on the valves etc.
Should be close to the same as the other cylinder.

-You could run some carb cleaner through
with the fuel, here some people
use a product called "seafoam"

-It sounds like that cylinder is either
lacking air flow or is flooding.

-Check the air filter and intake for obstructions,
also may need to check the carb main jet,
it may be too large, worn or maybe
even fell out.
Check the choke system as well, maybe the choke is on.