Blue smoke after closing throttle, Curvy.

I use my 99 curvy as a trackbike. bought it a year ago after it had been stood up for 2 years with 12,000 miles on it, have used it for about 6 trackdays, but now coughing out blue smoke, but only immediately after you shut the throttle down,, also when you first start it, it backfires a few times via the front carb. had the airbox off to check for oil in it in case it was blowing up to the filter via the crankcase breathers, and it backfired with a bang and a puff of blue smoke between the carb and the cylinder head, thought the carb was gonna blow off as it jumped fairly.
a few people think it could be either rings, gasket, or valve guide seal.
anyone else had these symptoms and could point me in the right direction.

They're pretty solid guesses, closed throttle on the overrun causes a huge vacuum and is drawing oil past something for sure. Try a dry and then wet compression test?

[johnnyrod]

Sounds like valve seals, as said above, closed throttle means vacuum. Did you run it with the airbox off and that's when it went bang at you? Not a massive surprise to be honest, I don't think this tells you much. Yep get a compression test but if this tells you nothing then I would be more certain of it being valve seals. As you know you can't really use it on the track like this as it's going to spray oil droplets into the braking area.

[Jayneflakes]

My first thought was valve seals, but then I am no mechanic, just a tinkerer. Oil seeping past the exhaust valve seals would give you the blue smoke as it burns in the exhaust. No idea about the back fires though, although mine does pop a little when closing the throttle suddenly from a hard run.

[johnnyrod]

Popping through the carbs can indicate a load of air in the induction, which is no surprise with the airbox off, but is hardly a frequent event by the same token. Some fuel gets splattered back and forth as the intake valves open and close, it's not a smooth one-way flow.

Could be any of the valve seals, and it's such a job that you may as well replace all 8 while in there. There is a brief vacuum in the exhaust when you shut off (which is why leaks here result in loud backfires, air is drawn in - the odd pop isn't really a concern) but the intake vacuum is much larger on overrun. Like I say though, if there's at least one leaking, it's academic.

With the airbox off and the throttle open, you can see evidence of oil leaking past the intake valve stem seals, if there is any.

thanks guys, some food for thought there. looks like its a winter strip down for me, and get the zx6r I bought recently ready for track duty in the mean time.

[johnnyrod]

If you took all the oil out it's stop smoking