250-500cc Wr300 Cutting Out And Getting Hot

Well, my 2010 WR300 burned up a piston and cylinder after I couldn't keep enough water in it to keep it cool. It was cutting out at higher rpms on long climbs in the mountains. I finally got the engine back together with a new cylinder and piston. The bike starts easy, and seems to run really good except the fact it gets hot, and cuts out. I have completely moved the jetting from rich to lean with the same cutting out and heat issues. Also, I looked at the reeds and they seemed fine as well. Has anyone had any issues with the ignition timing moving around and causing issues? I'm at my wits end with this thing so any ideas will help.

Have you checked for a fuel supply problem to the carb? Possible pet-cock filter plugged or gas tank vent problem? Either of these will cause a lean/ over-heating condition due to fuel starvation.Good luck and hope you find the problem.

Yep, I drained the tank with the cap on and took a look at the fuel.

Possible water pump problem? Maybe the water pump impeller is not rotating with the water pump shaft resulting in poor coolant circulation= over-heating,cracked cyl. head?

Check for combustion gasses getting past the head "O" rings or head. This will cause the radiator to instantly build pressure before the coolant is warm and can get water in the cylinder and cause cutting out. Plus gasses will get in the water jackets and prevent heat transfer due to air pockets and cause further overheating problems. I would start the bike cold and rev it a few times and then immediately shut it off. Then as you loosen the radiator cap listen for escaping pressure.(there should be no pressure because the engine has not had time to warm the water) Now as a second check re-start the engine with the rad cap off and look for small bubbles in the coolant as it circulates. I realize you just put new gaskets and "O"rings on but there might be a crack, casting flaw or warpage letting pressure by. The leakage could also be in the cylinder itself but much less likely.

Checked the radiator. Sure enough, there are a ton of bubbles. There is some crummy machining on the top of the cylinder from the factory. It's to bad I just spent $300 having the cylinder repaired. This repair just got REALLY expensive. Thanks for your help troubleshooting this guys.

Be sure to check the coolant channels in the cilinder, there was a batch that hadn't drilled a coolant channel that prevented water from flowing.
There's a vid on Youtube about it.

What year bikes had the non drilled coolant channels? Or is this an ongoing problem? I was running hot and boiled over on the last ride and when I put my Hi-comp Head on the stock coolant looked "Burnt" and it only had about 5 hrs on it?

View: http://www.youtube.com/watch?v=8GHm7tPeyxs

View: http://www.youtube.com/watch?v=92A5zPF44c4

that's the vid I was referring to.
I believe it was 2008 model only, (so cylinder will have an 07 on it), I have two spare cylinders from 2008 and 2007, they don't have this casting flaw.
It was a small badge that had the problem, and can be rectified by drilling.

a faulty ignition can cause engine failures/seizures.check the spark.my 2012 WR300 had a faulty stator that caused an erratic spark.good spark,weak spark,no spark etc etc

I found that the screen in the spark arestor was plugging up at higher engine loads by a piece of the packing. That is the last screen type muffler I will ever buy.