Chainsaw Repair

I don't think the 4000 is an updated version. they were introduced at the same time. the 400 is more likely a price point unit. although $20-$30 isn't much of a difference for different regions.

differences? none. other than one lacking a purge bulb and the other having a 'satin' finish. I've heard people say the 4000's anti-vibe is better. I say nonsense. they have the exact same parts. they both make the same power also.
I will say when buying a gz400 new, you get a crappy semi-chisel skip lo-pro chain and the 4000 has an Oregon 91vg installed.