blue smoke from carbs

[richb]

Hi all,

I recently purchased a 1980 xs400 with about 16k on the odometer. The bike starts and runs just fine, with the exception that blue smoke flows out of the air intake when the bike is idling (probably also when moving, but its hard to tell). This mostly happens after the bike has had a chance to warm up. It does leak oil, but only a few drops at a time and I have been monitoring the oil level, which doesn't seem to be dropping too quickly. also, the idle speed which should be around 1200rpm usually sits at around 1500-1600, but will sometimes creep up to 3000rpm when the clutch is disengaged.

Are all of these issues likely to be related? Any input would be greatly appreciated, I am a capable enough mechanic if i know what I'm looking for, but I'm fairly new to working on bikes and need a little guidance!

[Airhead]

The only way you would ever see smoke from carb inlets is if there was a positive pressure, carbs should only ever be at atmospheric or negative pressure. Looks like your inlet valve (valves) are passing. check the valve clearance.

...Paul

[richb]

The only way you would ever see smoke from carb inlets is if there was a positive pressure, carbs should only ever be at atmospheric or negative pressure. Looks like your inlet valve (valves) are passing. check the valve clearance.

...Paul

is this something that will need replacement, or is it likely a case of making a few adjustments? in the meantime is it damaging to run the bike as it is?

thanks,

rich

[Airhead]

is this something that will need replacement, or is it likely a case of making a few adjustments? in the meantime is it damaging to run the bike as it is?

thanks,

rich

I would say it is damaging to run with valves that are passing, this can burn the mating surfaces of valve and seat, check valve clearance first. this would fall under the category of adjustment yes.