All 2st wr300 ceased 3rd ride

I purchased my 2013 wr300 about 2 months ago as a left over with no hours on it. I took it out for the third time yesterday, after about 4 hours of riding the motor locked on me as i was cruising in fourth gear. After a serious kick i was able to what i considered uncease it. After removing the plug and placing my thumb in the plug inlet, i came to realize it had no compression. Being that i'm not to knowledgeable on this bike i was wondering if i could get some feed back from you guys. I wanna know if there was a proper way to break in a 2 stroke motor and weather or not my dealer told me the wrong mixture for me to run which was 40:1. Any feedback would be help full at this point, thanks

40:1 is fine. You said you were "crusing" in 4th gear, is the bike jetted right? For a new bike to seize up, I would have to guess it was jetting related and you were cruising in a "lean" area of the jetting possibly? Hard to know for sure without more details.

Regarding proper ways to break in a motor, you will get all kinds of opinions on that! I always do 3-4 heat cycles of 10-15 minutes each on my 2 strokes, then ride them like I stole them. Never had any issues in the last 25 years, but I always jet my bike from the get go before I start to really wring it out so I know the fueling is good across the powerband.

More than likely , leaking reed block

Take it apart and see what it looks like.

I have a spare WR250 motor with a wide ratio trans you can drop right in, but to replace a motor on a brand new bike.....kinda uncool I know.

Are you sure you used 2 stroke oil for the premix?

Break in on this bike calls for 32:1 rather than 40:1. Ive sealed up my reed block with the 92-01 Honda cr250 gaskets and run a jd jet kit in the provided TMX. I also run lots of oil (32:1) and so far after 67 hrs on my 2014 WR300 - all is very well.

Heat cycles 30:1 pre mix each heat cyclye longer than last, dond lug the engine dont rev the hell outta it your bedding the rings to cylinder wall.
See if dealer will help towards repair cost if it was down to jetting it was sort of out of your hands.

if seizure due to leak in intake, it's a warranty item, go back to your dealer. I would.

Personally I wouldn't mention anything about cruising as the cause could be put down to this and a possible warranty void. If you don't think you have done anything major out of the normal run in procedures and asked, I would say "nothing out of the ordinary", not mentioning cruising. Let the shop determine the cause by a tear down.

Thank you. Ill take everyones advice into consideration, i will be drooping the bike off on thursday at the dealer n hoping for the best. Both from the condition of the motor onced opened and the dealers willingness to cooaporate with me. Im hoping there is a proper way of determining or diagnosing and faulty jet setup. Ill also bring up the reed block gasket and see what they have to say only after they give me a diag.

yep

Who is the dealer and where are you in NJ?