Developed a bizarre problem where the bike would start and run fine, but after about 5 minutes would start to run lumpy before quitting altogether and refusing to restart.
All of the following failed to find a fault - carburettors stripped, cleaned, checked and rebuilt, fuel mixture checked (with a CO2 meter and a Cleartune plug), fuel tank/tap checked/cleaned, ignition coil resistance values checked, spark timing checked, valve clearances checked, cylinder compressions checked, spark plugs replaced and correctly gapped and HT lead condition and resistances checked. All within spec and OK, so gave up and sold it on for peanuts as a non-runner.
YICS system makes it impossible to balance the carbs without a special tool. When the engine stopped, there was fuel, a spark, and good compression. Who knows?!
My first bike, bought for a couple of hundred quid so wasn't expecting wonders. To be fair, it was great for the first couple of tanks of fuel, but then developed a fault that was so bad, I spent the next four months trying to fix it, and gave up.
Before this, the engine was smooth and very torquey, and the bike was surprisingly lively. Comfortable and good on fuel too (50 mpg average). Would have made a great commuter / first smoker, but I never did find out why it kept cutting out.
After missing about the sixth consecutive rideout with my mates, I decided enough was enough. I'd got into bikes to ride them not to spend sunny Saturdays taking them apart for the umpteenth time, so I cut my losses and got rid of it.
It's the c.d.i. unit.
Use Premium Fuel Only... If there is any varnish in the carb = bike doesn't run. The diaphams are very sensitive. Adding a battery tender is a very good idea.
My XJ 550 did this. It was the fuel enrichment device (choke) sticking on ever so slightly, hence it ran fine when cold, but got progressively worse as the engine heated up. This was because the mixture was too rich.
Proved easily; if you let it go cold and it's OK when started again, until it warms up again. Or take the plugs out and see if they are sooty.
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