2 or 4 Cylinders

Hi all,
Stupid question but I'm a bit of a newbie. When I'm idling my xj 650 (which is quite difficult to do) it only seems to be firing on the 2 left cylinders (I took the spark plug leads of to work this out). When I take it for a ride it seems fine - with plenty of power (almost like a power band) It doesn't blow any smoke but you need the choke ever so slightly on to keep it idling. Could it need a carbie clean / tune??
Thanks
Peter

 

Yes and a valve check!

 

It's probably the carbs, but not necessarily.

Low compression can cause a cylinder to drop out. Run a compression check. If it's good your problem will be carbs. Do the valve lash while you're in there.

 

wow this is a bit weird. I turned the fuel tap around so that the arrow faced the back of the bike (which I thought was off - not ON or RES I can't remember the other one PRI I think) and anyway it seems to starting and running fine. It still won't idle without adjusting the choke but it is much better than before.
?????
Peter

 

Sounds like you switched it to reserve, you sure you weren't just low on fuel?

If you have the stock vacuum-operated fuel valve, there is no "off." Both "on" and "res" are vacuum-controlled and should not allow fuel to flow when the motor is off. "Pri" allows fuel to flow regardless of vacuum signal.

You should need "choke" (enrighening circuits) until the motor is warmed up; if you need to use the choke all the time then you need to service your carbs (and check the valve clearances so you can adjust the newly-serviced carbs.)

 

On a manual petcock (gravity operated), there is usually no arrow on the "knob" and you can't turn it towards the rear of the bike because there is no selection for this position.

On a vacuum-operated petcock (stock on our bikes), the aroow towards the rear is the PRIME position, and as bigfitz said, the fuel flows regardless of the vacuum, even when the engine is not running.