Bike seems to run fine, no issues so far - however in the 1000 km since the rebuild it has burnt quite some oil. Wonder where is it going?

 

Looking back at the cylinder picture...I'm going to say the rings can't seat well on that wall. It could totally be the picture, but I don't see any cross hatching on the cylinder wall. It looks porous. I'm guessing each stroke you leave a little oil behind.
Good opportunity to buy the stock KLX 300 cylinder and piston, it should work fine with the EFI, I think...
More power and be done with it and ride on a really fresh motor.

 

Ben, thanks for your input. I had these worries about the cylinder before assembly, but with no money for new parts I just went with what I had. The bike still seems to have decent compression, so far starting is easy and power is good. I put in new valve stem oil seals when I rebuilt the bike, I wonder if I might have screwed (some of) them up during installation... I used an appropriate-sized socket and light taps with a hammer to seat them in place, but that was my second time doing that, maybe I was too generous with the hammer and damaged the seals?
I guess there is not much harm running it like this for now, and adding oil as needed?
I'm gonna go on a >1000 km trip to Malaysia this month, I don't want to do anything to the bike until I return.
I'd love a KLX 300 cylinder and piston, I did some research on how much it will set me back, and I simply don't have money to do that now (got a baby coming in a few months from now!) - mostly because with the stock ECU the 300 kit will run too lean, so it needs a PowerCommander+AutoTune or a similar unit, which costs more than the cylinder+piston kit itself.
Another guy living in Thailand was gonna get a big bore kit some time soon, and offered me his old (almost new, just a few thousand km) cylinder and piston. So I'm waiting for that now...

 

Well just keep the oil level up until you can fix it again.
Could be worth checking the valves stem seals but I bet they are ok, unless you really think you might have messed one up. I'm guessing that would be a real hassle, but less of one than a bike with a problem. I've never taken any valves out of the head but I fear it's coming. It will be a learning experience for me. I understand how it's supposed to work but practical knowledge isn't the same as book knowledge.

And congratulations on the upcoming addition to your family!

 

Right, that's what I gonna do. Removal of the valves is not difficult, provided you get or make an appropriate valve spring compressor. The piece of small-diameter PVC pipe with holes cut out on the sides was OK to use, if not very comfortable for the hand. The trick I found on the net about using a small magnet to get the retainers out was very handy. Watching some YouTube videos helped my confidence.

Thanks man! That will be a real learning experience

 

Hi iam from indonesia.
Its my first time to write in this forum.
Before iam sory to my grammar not to much..

I want ask how to fix problem klx 250 efi 2009 backfire /pooping even i declerated.

Subtrottle buterfly off.
Install juicebox.
Muffler jardine.

I apreciaed for anythinh answer..

 

You would get more replies if you start a new topic.
As for your issue, was it always like that since you installed a juicebox and a new muffler, or did it run ok for some time then the problem started?

 

I got this bike in these conditions.
That is why I want to ask, does others have the same problem?

 

Pardon the irreverence...

Did you look under the tank to make sure no one slipped their old CV34 carb in there and swipe the EFI?











Sorry... the goofy thought hit me when I saw the title again today and I had to say it... Hope you guys get the humor.