Looking to wake up my 99 big bear 350 4x4, looking for a good crankshaft with connecting rod, or a complete 400 engine that has issues. Thanks

 

Can't help you there but I see what your after.

The 348 and 386 are the same motor just with a different stroke. 64mm vs 71mm. Both have the same 83mm bore.

Problem with the Big Bears is their low gearing, the motor scream at 45mph and begs for a 6th gear.
Even if the ATV had a 500 it would scream at 45, not sure if it's worth the work.

 

I was considering putting 28" mudzilla s on it, and was concerned it wouldn't have enough low end to turn them, and I just got a locking front diff for it as well

 

Your ATV is geared low and may handle 28 mud zillas since zillas are the lightest mud tires made.
If not a another option is a gear reducer kit or clutch kit. here is a good read before you decide.
Yamaha big bear 400 gear reduction?? | High Lifter Forums
The 386 does not have much power over the 348.

 

I appreciate your help! !

 

It appears to be 5 hp more from what I found on the Internet, but then again it is the internet!

 

Some of these guys are running 28" Vampires on their Big Bears and those tire are much heaver then Zillas.

You could go 27" Zillas for a safety margin. My 350 Bruin had 26" Zillas and handled them easily and that ATV had no low range.

 

And we are talking about the same tire, apparently there is a zilla which is milder than the mudzilla that I have.

 

Your right, the Mud Zilla is more hard core . The Zilla is still impressive with a 1.2" lug. Maxxis Zilla .

A example.
The 28-12-12 Zilla weighs 27lbs

The Mudzilla 28x12-12 weighs 43lbs.

 

That is a big difference, Im wondering if I should just stick with the 26" super swampers that are on the machine and hope that the diff lock helps