Any body know what happend

50:1 amsoil  93 pump gas just clean air filter

It's hard for me to tell exactly what went wrong from the pics, but I get the feeling there are a few things that contributed to this. Are you running an Outterwear on the air filter? It seems like you were not getting enough oil.

What size TMX?I,m no expert but looks very lean to get that hot on the exhaust side,heck it even melted the electrode of the plug by the looks of it.What speed were you riding at when it happened?

Any body know what happend

The 1st and 3rd picture shows seizure marks are all in the upper half of the piston skirt indicating an overheated piston.  A piston operating at its optimum temperature would have had seizure marks equally from the top to the bottom of the piston if the piston clearances were set up incorrectly, or if the piston/cylinder wall was lacking lubrication or if insufficient engine warm-up before riding it hard. 

The top of the piston shows detonation around it's circumference.  The light etching or very light sandblasted look at the outer circumference is the result of detonation.  When an engine goes into detonation the piston will severely overheat in a matter of seconds.  In these last few seconds, the upper portion of the piston will expand enough so that the piston becomes a press fit in the bore.  Once the piston becomes a press fit in the bore, the friction and speed at which the piston is traveling in the bore will generate enough heat where the oil breaks down.  Once the oil film breaks down the friction is increased even more.  In the absence of any lubrication between the piston and the bore it does not take very many engine revolutions before the surface of the piston skirts melt and transfer a film of aluminum to the bore.

Incidentally, the 1st and 3rd pictures of the piston shows that this is not the first time the engine has seized.  Prior seizures or heavy scuffing from detonation were mild enough that it did not smear aluminum over the rings to the point that the engine did not have enough compression to continue to run or restart.

Fresh seize marks will be silver in color or look like raw aluminum and prior seize marks will be dark looking scuffs or smears on the piston skirts.  Prior seizures or times when the engine was starting to "tighten up" were ignored.  The engine was telling the rider something was wrong.  The rider continued to ignore the warnings and eventually killed the piston. 

The picture of the head also shows detonation around the outer circumference.  The carbonless head is an indication that the surface of the head was cool, indicating that the cooling system was doing its job.  Carbon only sticks to a surface that is hot enough to coke the fuel and oil that touches the high temperature surface.  Extreme combustion temperatures can burn off the crusty part of carbon on the top of the piston and combustion chamber surfaces, but it will not look like the head surface pictured.  If the combustion chamber in the head had originally had a layer of crusty carbon or was just discolored and was exposed to abnormal combustion temperatures the carbon build up would have been consumed but it would still have a much darker color that the head shown in the picture. 

In summary: the piston failure was due to detonation.  Detonation can be caused by any one or a combination of the following conditions.

1.  A slight lean condition
2.  Ignition timing that is too advanced
3.  An exhaust system that is too restricted.
4.  A poor engine design or combination of bolt-ons or modifications like a bad combustion chamber design, a poor exhaust system design, the engine may have been operated in an RPM range that the pipe and ports were not designed to operate.)
5.  Fuel octane rating that is too low for the engine build and conditions present at the time of piston failure.

It's a mikuni tmx carb with 260 main jet has vforce 3 reeds fmf fatty uni car filter

Can,t remember for sure but I was running a tmx38 for awhile and think I was around 380 main jet.I,ll check and see if I have some notes to verify.

Nice wire up thanks the stock tmx jet was 370 and what gas should I run next time almost done rebuilding it now

While you're in there be sure to use the RM wrist pin bearing and aluminum thrust washers if you haven,t already.

Lol, i run 38mm tmx no air lid, uni air  filter i use  410 or 420 main jet !!!!