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Just bought a new to me KDX250 for $500 came with a paddle tire and a newer rear dirt tire, with an even newer front tire, and it has a new top end with 3 rides.
only issue is it does not run, it quite getting fuel (or atleast thats what he thought) , and thats why the kid sold it.

it turns over freely, and feels like compression is good, once i track down a tester we will test for real (what is stock compression?)
the spark plug is brand new and its getting spark, the air filter is clean and looks new, we tore down the carb and it was clean and clear, the reeds looked ok, we tried to pour gas directly into the cylinder but it would only backfire, and thats as far as we got today, maybe someone will think of something we didn't


Only other issue with it is all the danm sand! i hate sand so much, its in everything, i feel like im going to have to tear the bike completely down to rid it of all the sand, we jokingly thought that maybe she just got tired of all the sand and went to sleep, but after multiple promises of never touching sand again she didnt wake up, sad.

Any and all help and advice is appreciated.

Have same prob with another bike. Ktm 300 mxc

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maybe try running it without the exhaust on it
gas can only go one way and if everything is clear on the way into the engine there almost has to be an obstruction on the way out of the engine

ill try that when i get home,speaking of the exhaust it leaks oil like none other out of the exhaust, drips down onto the swing arm. but exhaust does come out when it backfires


it was a sand bike, is it possible sand and oil could have built up in the pipe and cause restriction?

problem with sand bikes is that they collect sand! Doesn't take much to do a lot of harm to the motor. Take the carb off and completely disassemble it (don't just spray a can of cleaner through it). Clean it thoroughly, and when done...do it again. Ensure your intake/exhaust tracks are mechanically sound (no holes/tears in boots, reeds good, silencer repacked, clean filter, new plug, etc). Run your fuel line into a clear jar and see what kind of flow you have from the petcock, very common for sand bikes to have flow issues there as the sand clogs up the petcock screen. These bikes are very simple and need only 3 things to live...fuel, air, spark...make sure all 3 exist and problem solved!

Please just post 1 question in one forum.

Have you taken off the exhaust pipe to take a look at the piston?

Jason wrote:Please just post 1 question in one forum.

Have you taken off the exhaust pipe to take a look at the piston?

Mybad man, i just didnt know where to post, wont happen again.

No problem at all,

Good luck on the KDX250.

bufftester wrote:problem with sand bikes is that they collect sand! Doesn't take much to do a lot of harm to the motor. Take the carb off and completely disassemble it (don't just spray a can of cleaner through it). Clean it thoroughly, and when done...do it again. Ensure your intake/exhaust tracks are mechanically sound (no holes/tears in boots, reeds good, silencer repacked, clean filter, new plug, etc). Run your fuel line into a clear jar and see what kind of flow you have from the petcock, very common for sand bikes to have flow issues there as the sand clogs up the petcock screen. These bikes are very simple and need only 3 things to live...fuel, air, spark...make sure all 3 exist and problem solved!

Yea, i skipped over this bike on CL two times only BC i saw the paddle tire, but my friend who rides all the time texted me about it and was super excited so i took his word and jumped at it.

and like i said in the original post, the air filter was clean, maybe even new, spark plug was new, and we tore the carb down and it was spotless and free of anything, After talking to his dad i think the timing is off, so im going to check that when i get a chance.

the promising thing is i cant push it in gear, so hopefully a compression check will confirm this.

Jason wrote:No problem at all,

Good luck on the KDX250.

Thanks! im hoping i figured it out, found a few people with KXs having the same issues and it ended up being timing, or the pin in the fly wheel sheered and it moved, because it will backfire every 10-15 kicks, and when we put gas straight in it it backfired also, so tomorrow after work i think ill dig into it a bit more and see what i can.

Im way into this bike though, and pretty happy with it at $500, already racked up a big list of things i want if i end up liking it hahaha

wheelerboy12 wrote: After talking to his dad i think the timing is off, so im going to check that when i get a chance.

I had a Suzuki TSX once that I wanted to replace the points on
so I pulled the flywheel off, replaced the points and got everything back in speck

I was just about ready to put her back together when I noticed I had lost the key somehow but I figured it couldn't be that big a deal

so I just eyeballed it and torqued everything back down

one kick and she was purring like a kitten
I put her in first, let off the clutch and the bike lurched backwards


I guess the timing was so far advanced it would ignite before the compression stroke was completed and kick the motor around backwards



so in short, if the timing is off it should still run

yeah, a sheared woodruff key isn't a common thing. Generally if timing is off it's because someone went in there and messed with it. Do the simple stuff first