I have a 2001 Warrior quad 350. I lost the baffle

Hello, Get a FACTORY service manual and FOLLOW it to the LETTER and DO IT RIGHT!

2001 tenth digit in a 17 digit serial # is the year on all vehicles cars, trucks, bikes, ATV,etc.

you are fouling spark plugs. the atv is running way too rich. either the air filter is super dirty or exhaust has been modified (race pipe, baffle removed, etc)

if none of those have been done then maybe your carburetor needle is stuck open and is flooding the motor and the carb needs cleaned.

Do I take it the engine is already stripped to establish the fault. I've owned several Honda's and never seen this fault. If its in bits a good motorcycle engine shop could do it and recut the seat but only a search of parts books would tell you if Honda used a motorcycle head. Saying that, Honda do appear to use modified bike engines to power quads. New crank cases built onto a previous barrel and head.
Call a Honda specialist or a quad shop who may have already worked it out for themselves. Check out quad forums as well?

If you have good spark then it's most likely a fuel issue, anything off of idle is dealing with the main jet and metering needle, clean jet and check needle for excessive wear.

Replace the idle jet (don't clean) with a new one from a Yamaha OEM only $5.00 & make sure the idle mixture adjustment on the bottom of the carb. is set 3 1/2 turns out from seated in (a brass screw ---Don't over tighten & break off the needle tip). Also , be sure the choke is all the way off or it won't idle either.

clogged choke jet or passage for sure.

95% of the time it's the Stator / Pulser coil in the L.H. side of the motor.

Check spark plug, that sounds like it's running little too lean.

NO--- If you clean the case spotless of oil, 5 minute two part Epoxy will seal it. Let it set over night.