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I got a klx300 from 2005 got a new ish top end and had 150 pounds of compression 2 days ago then yesterday it got hard to start and was running like crap and after I parked it last night around 2am it won’t start now and it’s showing 80psi and it’s real easy to kick I had to just about Stand on it to kick it before 

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33 hp from 292CC , that's pretty good --- wish my TRX300 put out 33 hp , think it is around 20 hp 

 

being you said " newish " top end , that makes me think you have a bad crankshaft and or rod and the piston was wobbling and gave short service on that last rebuild ---- squirt some motor oil into the cylinder and do a wet test and see if compression goes up , then take it apart and see what came apart 

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Tried a wet test and this is it apon further inspection the cam lobe is holding the intake valves open

image.jpg

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Can You get a picture of Your timing marks left side cam sprocket and fly wheel on the compression stroke ? Then without turning it a picture of the right side of Your cam lobes ? 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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If you are doubting your on compression stroke ----  Take out the spark plug , put your finger over the hole , lightly bump the engine over with the starter button , when you feel the compression starting , stop bumping it over and move it to the timing mark with a socket 

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2 hours ago, Fishfiles said:

If you are doubting your on compression stroke ----  Take out the spark plug , put your finger over the hole , lightly bump the engine over with the starter button , when you feel the compression starting , stop bumping it over and move it to the timing mark with a socket 

starter button? What’s that

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Just now, Harleydavidson said:

starter button? What’s that

Well then you have to kick it , without the spark  plug in you should be able to use you hand on the kick starter 

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When You turn the engine over slowly ( counter clock wise )  and You see the intake valves open with the cam lobes the next t on the flywheel is top dead center on the compression stroke.

 

At this position check Your valve clearance.

 

I cannot blow up the pictures enough to see You timing marks on the sprockets. The intake cam lobe looks to be in the correct position cannot see the exhaust lobe because the auto decompression works are in the way.  The lobe should be in about the same position pointing outward as Your intake cam lobe.

 

These twin cam bikes can jump time for various reasons they can also spin a cam ( sprocket that is just pressed on, spins on the cam,) lobe timing is them WAY  off.

 

Just repaired a 2021 KX250 with 19 hours on it that spun the cam and bent a valve.

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14 hours ago, oldmxrider said:

When You turn the engine over slowly ( counter clock wise )  and You see the intake valves open with the cam lobes the next t on the flywheel is top dead center on the compression stroke.

 

At this position check Your valve clearance.

 

I cannot blow up the pictures enough to see You timing marks on the sprockets. The intake cam lobe looks to be in the correct position cannot see the exhaust lobe because the auto decompression works are in the way.  The lobe should be in about the same position pointing outward as Your intake cam lobe.

 

These twin cam bikes can jump time for various reasons they can also spin a cam ( sprocket that is just pressed on, spins on the cam,) lobe timing is them WAY  off.

 

Just repaired a 2021 KX250 with 19 hours on it that spun the cam and bent a valve.

Timing and everything is good on it took the head off and valves are fine no valve to piston marriage I don’t know what to check next

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Now that the head is off did You pour a little gas down the intake and exhaust to see if it held the liquid or did it run out the valves ?  I have the tools to do a leak down test before it is torn down.   Is there a problem with the automatic compression release ?

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1 hour ago, oldmxrider said:

Now that the head is off did You pour a little gas down the intake and exhaust to see if it held the liquid or did it run out the valves ?  I have the tools to do a leak down test before it is torn down.   Is there a problem with the automatic compression release ?

Compression release is good the exhaust is sealing not the intake I can take the head back off I never bolted it back on I’ll test it then

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Sounds good, just last week had a bike that lost compression while kicking it over, failed the leak down test big time could hear the air blowing out the carb, gas down the head a valve leaked big time.  Bike had sucked in a small bit of plastic from the filter ?  Was smashed in the valve seat, I removed the valve saw it wiped it off put it back together and all is good !

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1 hour ago, oldmxrider said:

Sounds good, just last week had a bike that lost compression while kicking it over, failed the leak down test big time could hear the air blowing out the carb, gas down the head a valve leaked big time.  Bike had sucked in a small bit of plastic from the filter ?  Was smashed in the valve seat, I removed the valve saw it wiped it off put it back together and all is good !

I’ll try that

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Sorry put the pictures are not that great to troubleshoot online, can say I specialize in race bikes MX.  If one is torn down that far it gets new piston and rings. I am not there to check ring end gap, piston ring groove dimensions and the like.  I also cannot see the wear on the nikasil cylinder it will happen at the bottom and top of the stroke.

 

Just trying to help and it can be very hard to do online .

 

 

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What are these little things that look like valve seals on the top of the package and every time a order a head gasket it comes with something like the little brass or copper looking thing what is it?

image.jpg

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1 hour ago, Harleydavidson said:

What are these little things that look like valve seals on the top of the package and every time a order a head gasket it comes with something like the little brass or copper looking thing what is it?

image.jpg

Top right look like valve stem seals , round copper ring is the exhaust gasket , not sure about the things on the top left 

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On the fly wheel the mark says TDC and right after it says F will it fire on any stroke or how do I figure it out

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20 hours ago, Harleydavidson said:

On the fly wheel the mark says TDC and right after it says F will it fire on any stroke or how do I figure it out

What are You trying to figure out ?  The ignition will fire the plug every revolution one is a waste spark as it is not on the compression stroke.

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