2006 Kx250f with valve clearance issue

I was out riding a couple days ago and after about 3 hours my bike decided it didn't want to idle anymore and when i kept on the throttle to keep it running so i could make it back, it backfired a lot. So when i took it home, i thought it must be something to do with the valve clearances. My inlet RHS and LHS clearance were within specs, now on the exhaust side, the RHS (.007) was within clearance, but the LHS was .022. So instead of the clearance wearing up, it's going down. How is this possible only on the LHS side and not the RHS of the exhaust cam?

Carbon build up most likely.  It can happen on one valve and not the other.  The other possibility is the top of the stem is wearing down, but that's not as likely.  It could be the shim was too small on the last re-shim.  That's all I can think of.  

 

You could re-shim and see if that helps, but maybe better to pull the head and clean the valves and seats.  Simple Green is good for carbon.  Putting the stem of the valve in a drill (protected by a hose) and spinning it on blue scotch-brite with simple green works well to take carbon off.  

 

Just a place to start.  I had a similar issue and cleaned the valves and re-cut the seats.  You might not need to re-cut them, but if you continue to have this issue, an incorrect contact surface between the valve and seat could be the problem.

Make sure your at TDC. Sounds like the decompression mechanism is holding the valve open causing your reading to be off.

Make sure your at TDC. Sounds like the decompression mechanism is holding the valve open causing your reading to be off.

 

That too.  I assumed . . . never mind, never assume.  Very nice, Josh.

Thank you guys, this thread is great. I'll be tearing it apart tomorrow and ill post what I find on here. I was thinking I needed to re-cut the seats but then I spoke with a local mechanic and he said he thinks it could be the valve guide seal which caused the valve to wear.

Dragon67 was correct, I wasn't at complete TDC which was causing inaccurate readings. Once I found it, everything was in spec but I still have the problem of it dying out at idle. It was late last night when i tried to start it so i didn't give it the time to really warm up but I'll know today. My next step is to clean the carb and maybe adjust my idle a little higher. I recently cleaned out the air filter which was completely black. So I'm not sure if it's getting too much air now and that the filter wasn't properly oiled. When I cleaned it, I didn't have enough time to go buy the correct oil so i just used soap and water to clean the dirt and there was still left over oil residue from the previous cleaning but I'm not sure if it is enough.

Your welcome. Lol.

Clean and oil the filter properly first.

Sorry I meant joshx221 lol

On a related topic, let's say your doing clearances with the head off the bike. Can you spin the cams so the lobes are pointing straight up and check the clearances? Or are the lobes eccentric (or coeccentric? Not sure if I'm using the right term here) around the cam?

On a related topic, let's say your doing clearances with the head off the bike. Can you spin the cams so the lobes are pointing straight up and check the clearances? Or are the lobes eccentric (or coeccentric? Not sure if I'm using the right term here) around the cam?

TTurner161: That's how I measured my valve clearances before and it lead me to think I had valve wear. The lobes will be pointing outward when it is TDC.

So the round part of the lobe isn't centered. Hmm...

So the round part of the lobe isn't centered. Hmm...

 

It is centered. On both cams, however the decomp mechanism on the exhaust cam is also at that center point so if you put the lobes straight up that decomp can alter your readings.

Edited by Joshx221

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