Looking for some help with my big bear 400. Just recently purchased and it will only run right in 4x4 when i put it in 2wd it just Boggs and jumps but back in 4x4 rides prefect. Help

 

When you write "boggs" do you mean the engine starts spluttering or simply that the bike jerks? If it is loosing drive to the back end, this is not uncommon. Older Big Bears had a tendency to strip the splines between rear axle shaft and crown wheel if a rear wheel bearing went, and was not replaced quickly enough. Diff bearings can collapse and lead to the drive locking up, then slipping, and would seem more like what you describe. UJs to the back end (not sure if yours has them) can also fail. If the engine is spluttering but only in 2WD it points to an electrical fault.

 

It just jumps around sputters and bogs down in 2wd but as soon as i click 4x4 it starts riding perfect no clicking or grinding coming from the rear

 

This would point to an electrical fault, where the 4wd wire is shorting the ignition wiring. There won't be a lot of wire from 4WD switch to the unit on the diff. and it won't come near to the ignition wires except at the headstock, so I would be looking for chafed or melted wires there. Faulty electronics are a pain though, and an earthing problem can throw weird faults, as can overcharging regulators. The electronics that control the 4WD unit could be taking too much power, but I would have thought it would then blow a fuse. You could disconnect it at the diff wiring plug and see if the fault still occurs as you switch from 2WD to 4WD.