lack of top end power, looking to rebuild.

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#1
lack of top end power, what to fix.

Hi,

I have had a KDX 200 for a few years but sadly has never run properly it has always lacked top end power, it doesn't peak out as a two stroke should. Any ideas what problem maybe? its a 1989 model, and apparently was rebuilt before got it, but never ran properly.

I took it to mechanic, they said the crank seals were leaking, it does always blow alot of smoke. Would the crank seal leak explain the lack of top end power, or could it be other things like the KIPS valve or simply the tuning is too rich? Perhaps when the engine was being ran it after rebuild the tuning was made rich, but since has never been adjusted back to normal??

the bike seems to start, run reliably, but without the fun 2 stroke peak.

thanks guys.
 
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_JOE_

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#2
Any of the above may cause your top end issue. I suggest looking at all areas mentioned. With the age of the machine, it is likely the crank seals are leaking, and it could probly use crank bearings also. At that time you should do the top end, clean the exhaust valve and carb, and check your jetting to see if it is much richer than stock. I would probly hold off on changing any jets until you freshen up the motor and ride it some. If it continues to lack top end then proceed with jetting changes. Good luck!
 
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#3
cool thanks,

seeing as planning to rebuild, what are good things to do while have engine apart, what hop ups ie like big bore kit, overbore pistons-are they safe?

Also with the bike in general, what are some good things to replace (what usually breaks down) ie bearings, seals, parts etc..I already reconditioned the front forks with new seals.

might even add some more modern graphics if I can find them.
 
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#4
Lack of top end power after a rebuild says someone put the powervalves together wrong.

seeing as planning to rebuild, what are good things to do while have engine apart, what hop ups ie like big bore kit, overbore pistons-are they safe?

Also with the bike in general, what are some good things to replace (what usually breaks down) ie bearings, seals, parts etc..I already reconditioned the front forks with new seals
While you're in the cases, check those main and con rod bearings. Bad main bearings sometimes cause crank seals to fail. Grab on to the flywheel and jerk it up and down, there should be no movement/noises (a little in and out/axial movement is ok). On the con-rod, hold the crankshaft steady and tug it a few times to feel for any radial play, there should be none. Use feeler guages to measure the con-rod side clearance.
 

G. Gearloose

Pigment of ur imagination
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#5
Stock is too rich, open the airbox and jet the carb it correctly
 
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#6
yeah I suspect the KIPS valve wasn't assembled properly. The bike is now leaking oil too, think is from the transmission. So I'll be pulling motor all apart. Not sure about overbore kit, don't want to make it too complicated.

I'd like to pay some attention to the suspension also, does anyone know if there is a guide for setting it up, perhaps with aftermarket parts too match height and weight. I'm about 5 9.5" and about 78 kg.
 
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#7
If the transmission is leaking around any seals, those can be replaced without splitting cases. Only the center gasket requires a case split.
 
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#8
If you gotta fix an oil leak anyway, pull the engine. I would be more inclinded to check the jetting. When I got my KDX it ran like crap. I opened the airbox, cleaned the filter, installed 150 main jet, 40 pilot jet, 2 turns out on the air screw, now it rips! This is with stock exhaust. Good luck!
 
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#9
Clean the carbon buildup inside the expansion chamber. A blocked pipe will kill your top end.
 
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#10
cheers, looks like will be pulling apart the engine..might need a mechanic to tune it tho

I recently put new seals and oil in the forks, seems popular to put in new springs, what are good springs to get? I'm about 176 lbs (80kg). Do I need to rejet the forks also?

and is there anything to do with the rear shock aswell?
 
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#11
There is no center gasket on that bike.

If the crank seals need to be replaced, the crankcase halves must be split.

Since it is a 1989 model, check for leaks behind the three depressions behind the stator. J-B Weld to the rescue.

There is no big-bore kit for that bike that allows continued use of the power valves. You didn't mention whether you know it or not, but the cylinder is plated, and one can not just bore it out at the local machine shop for a few bucks and be ready for an oversize piston. It would need the plating dissolved, then bored out and sleeved or replated (without the use of the power valves - no thanks on the time machine back to 1985 KDX200).