250-500cc 2011 wr 300 lost top end today.

Bike has just over 100 hrs on it. was planning on putting new piston in soon. Guess i dont have to wait anymore. Bike still has a little compression and nothing is binding. Mechanics gonna tear her down tomorrow. ill give everyone an update.

Full seizure on top dome of piston. Cylinder scuffed on exhaust side slightly. sending it out just to be safe. thinking either had to lean main jet or got some really bad gas. Plenty of oil and coolant.

what jetting specs ?

got to pull carb but the same thing ive been running since last january.

Got the update with new slide needle and everything. gonna go up one on the main just to be sure. Where we ride here in NC not on the main much anyway but I was when she let loose. sent cylinder out to be replated this AM. hopefully have everything back for the broxton bridge Enduro on Jan. 15

My 11 300 seized up too. I was at about 1/3-1/2 throttle in a sand wash. The only way I could get any color on the plug at that throttle was to put the clip at full rich on the gay needle. I am working with JD jetting to come up with a kit for the new bikes. He sent me a needle that is really close but no cigar yet. I am amazed at the power difference giving it a little bit more fuel at part throttle.

Got bike back together broke it in for about an hour last week. 16 miles into the Broxton Bridge Enduro piston let go again. New non ethanol gas. Went up to a 45 pilot and a 440 main. needle in the middle. Felt piggie rich in the woods. come out onto the road for a transfer section and she seized again. Anything other than an airleak cause this?????

I've seen a restriction inside the fuel petcock starve an engine when on the throttle for extended periods. Also, check the vent in your gas cap. Lastly check the float level. It may seem crazy rich when you are riding normal, but when the bike is pinned... fail.

Raise your needle to 4th.

Have you done the mod to the bowl plug/drain? I drilled a few small holes in the land by the threads so that fuel could fill the well where the main jet draws from. If the mod isn't done fuel has to spill over the top ridge of the plug/drain. I did this to mine because at WOT for long periods my bike would run out of fuel and die then restart and go on like nothing until another long WOT. Sometimes I could pull in the clutch and wait until the bowl refilled and bump start it. Drilling the holes solved this. My big worry was what if it starved it just enough to hurt it without warning it would seize.

If there is fuel shortage in the fuel bowl how could drilling holes in the drain plug help? either there is sufficient fuel and maintained at the correct level or there isn't.

The plug sticks up higher than the bottom of the bowl so if the bowl level drops low for any reason the well where the main and pilot draw fuel can empty before the fuel level raises enough to fill the well over the top edge of the plug. Other carbs come with holes in the well plug but mine did not have any. I did the mod and it seemed to make a difference. It could have been a coincidence and some other problem resolved itself at the same time I did the mod, besides it doesn't do any harm it so why not?

I agree that I can't see it doing any harm, I just think that if there is fuel starvation drilling holes wouldn't solve the root cause, only allow a few more seconds running. At WOT I don't think you will be using fuel quicker than the supply to the bowl unless there is a partial blockage in the tap, fuel pipe or float needle.

I thought the same thing and paid close attention to the wire hook that opens the needle, it seemed that it could have been letting the needle stick. After a few miles the needle started working better. Every little detail may not be the solution but added together makes a difference.

Got bike apart. piston looks great on intake side and top of piston looks great. doesn't look lean at all. Large chunk of plating came off at exactly the spot that was sent off to be repaired. Coincidence???? maybe but bike doesn;t liik like it seized from being lean this time. Looks like plating failure.

I feel better about my jetting now.