Hello, I'm Hutch...I have two warriors and a big bear. Could sure use a little help with these things. Not really fluent in ATV yet, but hope to be someday, anyway my 89 Big bear backfired and died. Got spark, got gas, seems to have compression, (but haven't tested it yet...next). She rolls over good, maybe too good...seems soft. Have spark and enough compression to blow gas mist out the plug hole when cranking. Suggestions, Been running great since we got it. Any help would truly be appreciated. I love these bikes, but all getting old and need loving care.

I have a 1994 Warrior, had it or over 20 years. Lots of stator problems but never compression problems. I think the engine on the big bear is similar?
Anyway...
If you have fuel and spark only thing left is correct timing and compression. Get you a cheap gauge from Harbor Freight and see if you have at least 100 or so. It might be a good idea to check the timing mark on the flywheel against top dead center of the piston if your compression is good. It would be very odd for the compression to go all at once if it was rings or valves.
My thinking is the flywheel key is sheered causing the timing to be off.
Let us know what happens.

I appreciate the prompt reply! I got a new plug. Appear to have good spark. (I was thinking it might be flooded, so I lit the cylinder.....wife almost died. It went off like a shot gun!) I got all the plastics off so I can check valve lash. pulled the gear cover and sight screw. The timing is off about 1/4". I can only guess that this is the problem. Could I have jumped time? I will get the pressure tester but it appears to have good pressure too. (Blows my thumb off hole) Been using either, and it blows a mist of gas out plug hole when rolling over. Chain and gear look good and seem tense enough. So what do I have to replace to fix the timing?
What would you recommend to fix this problem? Can I correct it by adjusting the valves? As I said, I love these machines, The two Warriors don't even run yet! lol. The Big Bear just died yesterday. I plan on doing a whole engine rebuild on the one. Will post video! Thanks again, and please, continue to walk me threw this! I have a little mechanical knowledge, but none on bikes.... How do I post photos on here? Thanks again Warrior Scott!

The Big Bear is a 350 isn't it?

I'm not sure, I thought so, maybe it's the grizzly with the same engine. Actually, I think there are 400s and 350s. depends on year I guess.

1/4" is within what you can check really. I doubt that's it.
You really should check the compression, it will save you time and money in the long run.
Valves don't un-adjust at once.

With a clean plug and a charged battery try cranking it at wide open throttle in case it's flooding.

compression gauges are less than 20 bucks on Amazon and about 30 at Harbor Freight.