First Ride on '15 EC300E

[celester]

Hey, I finished my first ride on my "like new" 2015 Endurocross just yesterday! Mixed the gas 50:1 like the company's manual suggests for synthetic 2-stroke oil, then rode mostly slow, rocky (1st or 2nd gear) single-track here in the north woods. When I did get into the pipe at the end of the ride, the engine suddenly fell on its face, bogged-down and stalled-out, but then would fire right back up and run okay at low rpm. Idle seemed a little high during the ride to me, the air filter looked pretty clean, and there was plenty of gas in the tank. Some unburnt fuel also dripped out of the silencer. I haven't pulled the spark plug yet. According to the dealer where it was purchased, the carburetor has already been set-up "perfectly" for Upper Michigan and to "just ride it". Also, today a staff member at GasGas US told me that the mix ratio should be around "35:1 and that the 50:1 listed in the manual is for the break-in period".

Any ideas on what happened, what the proper fuel mixture should be, or what I should do next? Hopefully I haven't damaged the engine...

[BassMunn]

Sounds like your float level is too low. That would cause it to run out of fuel when you whack it and would also cause it to run leaner and cause a slightly higher idle. Had this happen to me on my old Yam WRF

[Jakobi]

Hard to tell from the description, but advice would be to check the fuel flow.

If you have an inline filter check that it's clean/replace.
Check the breather lines for the fuel tank (check valve in cap breather) and carb lines.
I'd then establish a baseline for your jetting regardless of what the previous owner says. I'd pull the carb, check the float height, blow out the passages and jets, and record what you have as a baseline.
Inspect the plug, check the model and gap and consider replacing.

Oil ratio at 50:1 is OK if using a high quality synthetic and not sitting wide open all day long. Oil ratio and brand is a topic in itself, and more oil definitely won't harm anything, but 50:1 isn't silly lean and many run around that ratio with no ill effects.

You could have powervalve issues, your silencer could need a clean and repack, you could be loading up and fouling the plug at low rpm, or could be running lean and starving.. you'll need to start ruling things out to determine what's what.