I am getting a 1994 400 4x4 from my mothe rin law. She is in a different state and doesn't want to deal with it.
My brother in law has it at his house and told me what problems it has had:
it blows headgaskets a lot when used hard at slower speeds.
the magnet blew apart last time it was used.

Obviously I need to replace the magneto, but is there a common problem with the headgaskets on that engine?
My first guess would be to make sure the cooling system is in good shape,

Also, I am not sure if it is a 400l or a Sportsman 400. What is the difference?

I am getting it for free, but I will have to put some money into it for sure.

 

I almost guarantee that the water pump impeller nut has come loose. Either that or the first time it blew he installed the new one upside down (it is very easy to do).Sounds like you got a deal for free. Check and make sure the original piston is not in it. If it is I would go ahead and pull the cylinder and bore it. If the piston has been replaced then your in good shape. Take the head when you get it off and lap it on a sheet of 1000 grit sandpaper on a piece of glass. Use a little WD-40 while doing it. After just a few seconds you can tell whether or not the head is nice a flat. If it doesnt touch all over work it nice and even until it is as good as you can get it. Hope this helps,Bubba