Kx250f No idle,lots of backfire.

[Krossipoiss]

Back from track and with bad humor, as expected....
Now there's no/very little backfire and idle is pretty nice.
But while cruising with half throttle it just bogs/stomps.
Runs nice with a quater and accelerates also good+ runs good with full throttle.
Tried with 142,150 and 160main jet. Also all needle positions, but they didn't make any change..

 

[Krossipoiss]

New problem again- oil is at medium and with over half throttle it sprays out from Breather Hose. What could cause that ?
Piston has 2 hours on it.

 

[whenfoxforks-ruled]

Excessive pressure from somewhere, or a partially blocked vent?

 

[Krossipoiss]

What could cause that pressure ? Worn crank bearings and seals ?

 

[whenfoxforks-ruled]

What could cause that pressure ? Worn crank bearings and seals ?

Them also! I was thinking valve stem seals. And, fresh or not, the piston and rings?

 

[Krossipoiss]

Piston looks good and has max 2 hours on it. Rings set as wiseco manual told.
Stem seals are like new(worked for 1hour max)

 

[Ol'89r]

New problem again- oil is at medium and with over half throttle it sprays out from Breather Hose. What could cause that ?
Piston has 2 hours on it.

Possibly, upside down ring on piston or damaged oil ring from assembly. Did you make sure the marks on the rings were on top when you assembled the top end?

 

[Krossipoiss]

Does sb know tps ohm settings ?