KX250 sounds like a snare drum

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Jun 23, 2007
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#1
Hi All.

Not getting clean power from my KX250, and sounds like a snare drum though most of the rev range.

Also struggling to get it to idle. I have set the idle speed screw as per the manual, but wherever I have the idle speed screw set, I can't get it to idle.

I know I have the correct spark plug, and I'm using 200ml of two stroke oil per 5 litles of unleaded (1:25)

Any pointers?


Thanks,

Adam.
 
Joined
Feb 21, 2007
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#2
That snare drum sound is the sound you get when yuo have a shattered piston. The power issues are because, if you do have a jacked piston, you aren't getting consistand compression so the power is jumping all over the place. Take off your expansion chamber and take a look through your exhaust port and look for cracks in the piston. You might be replacing a top end...
 
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#4
There are about a dozen things that can cause it to do that.

Check to make sure your pipe springs are on and tight, also make sure that you have the brass gasket between the pipe and they cylinder.

If that isnt where the sound is coming from you have problems inside the engine.

As far as the problem with the power, if you dont have a cracked piston you are running the bike with too much oil.

Get some good oil, mix it 32:1 get a few new spark plugs and re-jet the bike.
 
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#6
Could be a loose pipe, motor mount ect... Kinda hard to tell without examining your bike first hand.

If your bike is in good mechanical order. Ie... filter clean, silencer packed, good topend, all bolts/mounts tight... Could be a lean condition. Try stepping up one or two on the main. See if you feel/hear a change.

If you determine it's the jetting; get the highest octane fuel you can find, 93 would be a good choice. Mix fuel oil at 40:1 - 32:1 with a good quality 2 stroke oil. I use Mobile Racing 2T at 40:1. Set the jetting back to stock and rejet with fresh plugs.

Good luck, Steve.
 
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#7
Ok, made some progress.

Re-packed the exhaust (there was hardly anything in it!).
Checked the piston through exhaust outlet and piston looks fine.
Exhaust fits tight to engine, though no gasket!!!
Spark plug looked good - no fouling
Enriched fuel to a 32:1 mix, and changed to 97 octane from 95.

Bike now still not idling well, and still has snare drum sound at low revs, but now runs smoothly when throttle open, and accelerates like a banshee right through the rev range.

Guess the next thing is to strip and clean the carb and do something about jetting???

Could the timing have anything to do with it?

Would the power valve have this effect on low vs high revs?
 

Moose

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#8
Well, I wouldn't go as far as messing with the jettting/timing/valves, just to get it to idle. If you do a search and look through previous threads, idling an MX bike isn't necessary, and is kind of safer than having one that idles.

Definitely clean your carb, if you haven't in a while. Other than that, if you've done a thorough check-over, then I'd say the snare drum sound is normal.

Maybe provide a video, with sound, of the noise you're hearing. That'd help everyone out.
 
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#9
Sound advice I reckon. Will try and remember to record next time I'm out and post.

Thanks,

Adam.
 
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#10
2-stroke MX bikes dont idle to well.. Mine doesn't It will go for about 5-8sec off the throttle in neutral before it starts to die (the best i could get it) But look through the threads i dont know of to many people that their 2-strokes actualy idle...