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Autodecomp question on 1990 xr600.

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Hi, This is my first post on TT.

Im worried, if my valves are leaking on my xr. (the bike is a 10,000 kms bone stock xr 600 1990) starts easy and runs good,

The reason is, because some people say that they can STAND on the kick lever in TDC without having it to pass by..

If i slowly kick my bike over to fint the tdc spot, i sure feel the hard spot,

BUT

its no harder than i can use my arm/hand to pass it. In other words there is NO way i can stand on the kicklever, for comparsion i also have a Yamaha yz400F

where i can stand on the kick lever in tdc.

If i back off the right exhaust valve adjuster screw so the autodecomp is

no longer pushing the valve open, should i then be able to "STAND" on the kicklever in TDC??

Maybe the previous owners 0,2 mm TIGHT valve clearences have

caused the leaking valves. then its time for a head rebuild...

//Richard

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Maybe try adjusting the valves to the correct clearances?? That would be the obvious first step.

The XR600 compression IS pretty stiff but not impossible to kick through without decompression. I did it for a short time before I learned how to to it correctly. Luckily, I didn't hurt either the bike or myself in the process.

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ok,, i forgot to mention that i have already adjusted the valve clearences to the specified numbers 0,10mm in /0,12mm out.

and... i can still use my hand to rotate the engine (and its not that difficult)

Yeah.. I kick my yzf 400 without using the decomp 3 times if i want (No need) but thats it..

I know what a hard kick would be like. And its definitely not there on my xr 600:bonk:

Iam now gonna make a test.

If i set the autodecomp out of order

Maybe i will be able to see if there is better or same compression resistance.

I will tell as soon i know..

Thanks for helping me..! TT is the best dirtbikeforum ever!!:)

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It sounds like you might have worn out piston rings. My 88 did the same thing, When i bought it almost 2 years ago i could almost stand on the starter, but by last november it felt like there was hardly any compression and it started to smoke When i measured the rings they were way out of factory clearances

I just finished rebuilding it and the "hard spot" is back and it runs like a champ

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I say just keep riding it. When it starts blowing oil out the breather it's time for rings at a minimum and maybe a new piston and bore. If it's a burned valve it will get worse relatively quickly. As long as it runs well enough for you keep riding it.

Most of the time that I have owned my XR600 it has not had the best starting compression. I just ride it until it gets bad enough to address. Until then :):banghead: :banghead: :foul::p:busted::crazy:

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The auto decompressor will disengage if you use the kicker to slowly rotate the engine through 2-3 cycles while holding in on the manual decomp lever. An audible "click" will be heard when the decomp releases. Then you can get a good idea of how much compression the engine has.

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Are you confusing the auto desompression release thats on the cam and you have no control over with the manual decompression release lever on the clutch side of the handle bar. You can back the manual decompression release cable off so it cant release anything but that doesn't change auto decompression release (Correct? mine didn't have one when i bought it) that is on the cam shaft and works without you doing anything. With the Auto compression release the standing on the kickstarter isn't going to happen but I'm sure there are some small guys that could stand on the starter of a bike with no auto decompression (have hotcam or have removed/welded the stock cam to work without the auto decompression parts) and it wouldn't go over TDC. I'm not in that category though. :)

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Thanks for all input.

I have now tested to put the autodecomp out of work.

I loosened the right ex.valve adj, locknut and backed the screw up like 2 millimeter or so.

Just enough much to make sure that the autodecomp doesent reach the valve.

When this was done and all valves were completely closed, i acheived a compression that was big enough to hold my own wheigt (79kg) standing on the kicklever a short time.

I have now got proof that my engine is in perfect condition, and learned that

the autodecomp works, and in a way that tricked me to thought that my engine was bad. :) Welcome to the autodecomp heaven..

// Richard

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Good to hear you figured it out and could feel the compression. Just make sure you adjust your right exhaust valve back to the proper clearance now that it has 2mm of clearance, before you start it up. :)

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Good to hear you figured it out and could feel the compression. Just make sure you adjust your right exhaust valve back to the proper clearance now that it has 2mm of clearance, before you start it up. :)

Yeah, i adjusted all valves the specified numbers one more time, when i already haved the tank off.

//Richard

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