OK, what the heck did I do? Better yet, how do I fix it?

Have you ever done something that has you wondering what the heck happened? I sure did! Last week I thought that since I haven't ridden my XR400 for about 6 months I would check the valves to see if they were in need of adjustment. Although I have done this a number of times over the years, I always use the shop manual for reference. With the exception of the right exhaust valve being a little tight, which I adjusted, all went well and I was quickly (for me) done. When I went to kick it over, I realized that I somehow managed to render the auto compression relief ineffective. When the piston would get to TDC it would barley budge. Sort of like it had extreme compression. I could get it to start and run (which it did very well) but I felt like a little girl trying to kick start a Harley. Any ideas what happened? And better yet, how do I fix it? If you know, would you please help me? Thanks for your time and assistance.

Did you happen to turn the crank clockwise during the valve adjustment?  This is a big nono, try using the manual compression lever to start it.

One possibility you adjusted on TDC exhaust instead of TDC compression hence exhaust valve seamed tight and you adjusted too loose so exhaust valve is not opening normally

Course would not expect it run well like that so perhaps not

The right hand exhaust valve is the “auto compression release” valve.  Are you 100% sure the auto compress mechanism was not activated when you adjusted that valve? I would go over the valve adjustments again, I doubt you have a problem if the bike was running fine before.  

Try redoing the valve adjustment, but first checking the freeplay on the compression release lever, or better yer, disconnect the compression release lever cable.

Did you mess with the valve rocker cover? The plunger that activates the right exaust valve can get stuck. You can also remove the valve rocker cover and check if there is anything weird with the auto decompression mechanism.

If it ran fine before and the right exhaust valve needed a large adjustment, then you probably had the decomp. engaged.

BR that must be it.It could happen to anybody.Always re check your valve adjustment before starting.

Thanks to all who read my post and responded to it. In reply to one response, I know about (per the manual) not to turn it clockwise and am positive that I only went counter-clockwise. To another response, I disconnected and removed the manual decompression lever and cable many years ago. And yes, it did run beautifully prior to parking it for the 6 month period when it just sat on its stand waiting to be enjoyed again. When I decided to make sure all was ready to ride again, all I did was change the oil and filter, pull the carb and remove the float bowl to make sure it was empty and clean without any old gas in it that may cause an issue, change out the air filter since I have found the filter oil sometimes works its way downward leaving it somewhat dryer towards the top and too much at the bottom. Since I removed the plug to make it easier to turn over to line up the timing marks, I put in a fresh plug. Then I checked the valve clearance, to which as I stated in my previous post, I only found the right exhaust valve to be tight. The other 3 were right on the money. I then rechecked all of them to make sure that the clearances were still good before I buttoned everything back up. Lastly I filled the tank with fresh gas, set the air pressure in the tires, lubed the chain, and loaded it up in my pickup. Did I bother to start it before I loaded it in the truck? No! Reason being, that I had done all the aforementioned, and based on years or nothing but utter reliability from this bike, I thought I was about as ready to ride as it gets. Sure, when it was so hard to kick over I should have known something was off. But since it did start, although not easily, I took it for a ride. Only when I stopped to take a break, and then tried to restart it about 10 minutes later, did I come to the conclusion that I had somehow managed to screw things up. I hope this longwinded rant helps those of you who are so helpful in figuring out where I went wrong. Thanks again for taking the time to read this and offering your advice. Since this weekend is filled with honey-do jobs I have to wait til tomorrow evening to get back to working on it.

On a different note, the feeler gauge offered by Motion Pro is the best I have found for checking the valves on the XR. It's size, shape, and price, make it a must have tool. I just thought I would share that in case you have been trying to make due with a typical automotive type.

I would have removed the auto decompressor and kept the manual lever.


"Sat for six months" could be some buildup on the pilot jet and fuel screw passage.  You may need to replace the pilot jet and maintain the fuel screw components.


"Float bowl drying out"  This can cause the rubber tip on the needle to dry out and crack as well as the fuel screw o-ring.


Since ethanol, it's hard on the carb to not ride the bike every week.

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