KDX200 - what happened to my top end???

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#1
Hi All,

This is my first post in this forum and I am hoping someone out there has an idea of what is wrong with my bike.

I have an 87 KDX200 that has no power in the top 1/2 of 1st and 2nd gear. I have to short-shift these gears in order to ride it w/o it over reving.

I had the clutch plates changed thinking this would cure the problem but it did not. Could it be a carb / jetting problem??

Any (logical) suggestions would be greatly appreciated!

GS
 
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#2
Does the bike work ok in the other gears, and only seem to blow through first and second? If so, my thought would be that someone has put a too small front sprocket on it, making first and second so low that they have become useless.
 
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#3
other gears work fine. The spocket has not been changed (for a long time). If the teeth are worn on the front sprocket could that cause the problem only in the 1st 2 gears?
 
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#4
Does the bike seem to run correctly, in any gear? Does it blubber, or miss in the lower gears, or just seem to go flat? If you hold it in third, does it continue to pull strongly as it revs? Has this been a problem that developed gradually, or all of a sudden? And no, a worn sprocket would affect all the gears.
 

dirt bike dave

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#5
Yes. Your engine has more mechanical advantage over the chain/sprockets in the lower gears, so it would be more likely to spin the sprockets inside the chain in the low gears. But this would only happen if one or more sprockets and/or chain are totally worn out. Are they? :D

BTW, each tooth on the front sprocket gets used about 4 times as often as the rear, so it is not uncommon for the front to wear out first.
 
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#6
Dave, I would think that a sprocket that is so worn that the chain slips around it would likely have no teeth left on it after even one ride (I'm guessing, I've never worn one out that badly:confused: ), so it would be noticeably slipping under any load wouldn't it? And it would certainly be very noisy when the chain slipped over the nubs, so that should be easily noticed.
 
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#7
I think I should replace the front sprocket as it does have some teeth in a pretty worn state.

As for Spanky's questions - the problem seemed to come about quickly and the 1 and 2 gears do go 'flat' almost immediately after cracking the throttle (If I kept it in first I would still keep going but I would be reving way to high). In 3rd it is fine, I can get on the pipe and it pulls fine.
 

dirt bike dave

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#8
Spanky,
I've never worn one anywhere near that bad, either. But I saw a guy with an XR once and it was pretty amazing that he could still ride the bike. If a normal front sprocket tooth looks like the Himalaya mountains, his were like the Appalachians. I can see how it would hook up under low load but spin inside the chain at WOT in low gears. It might not make a lot of noise, either, if the teeth are 'filed down' that far, but would feel more like the clutch slipping (which is also something Green Streak should look into).

I've also heard of one or more teeth breaking off, but I think that would be easier to notice than even but extreme wear.

IMO, the front sprocket should be replaced more often than the rear and the chain. The $15 worn out front sprocket will accelerate wear on the $50 rear sprocket and $80 chain. My theory is to replace the cheapest, fastest wearing part before it trashes the other bits.
 

dirt bike dave

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#10
Yeah, that one should have been replaced long ago. When you get a new one, lay the old sprocket on top to compare how much it has worn. Long before the front sprocket wears as much as yours it is causing premature wear to your chain, IMO.

If your chain and rear sprocket are also worn out, they will quickly wear out your new front sprocket, so you might consider a whole set.

With some bikes, you can extend front sprocket life by flipping it over. But the time to flip it is before it gets worn out.
 
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#11
thanks for the help. I will replace sprocket and check out the chain as well. Once done I'll let you know how it runs. Hopefully this is the fix.

Blue Strreak
 
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#12
That sprocket is worn, as evidenced by the "hook" shaped teeth, and it definitely needs replacing, but the length of the teeth is still fine, so your problem isn't a slipping chain, unless it is the rear sprocket that is worn enough to allow the chain to slip over the teeth. I would also rule out a slipping clutch, as they slip worse in higher gears, the opposite of your problem. Is the power-valve opening properly? If it is stuck closed, the engine would make very poor power at higher revs, making it seem like the powerband stops short. It is not as noticeable in the higher gears, because it takes the engine longer to reach the revs where the power falls off.
 
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#13
Originally posted by Green Streak
(If I kept it in first I would still keep going but I would be reving way to high). In 3rd it is fine, I can get on the pipe and it pulls fine.
If the motor revs higher and the bike isn't accelerating doesn't that mean something is slipping? I'd lay money it's the clutch.
Doesn't sound like a power valve problem. The sprocket doesn't look worn enough to slip. Being a cheap ******* I occasionally run sprockets until the teeth break off so I may be an expert on the subject. If your running a chrome moly front and aluminum rear the front will last about twice as long as the rear even though each tooth sees four times as much use.
 
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#14
Well, the clutch is very easy to test. Pull the front wheel up to a tree, or some other solid object, shift into top gear, grab a handful of throttle, and let out on the clutch. If it is slipping, the engine will stay running, if it is not slipping, you will kill the engine.
 
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#15
Thanks for the tip onn how to check my clutch. I hope it is not my clutch though as Johnin KY thinks. As I mentioned in my original post - I thought it was my clutch as well, and had my clutch plates replaced (friction plates were OK).