The GN400 makes a great project bike, very easy to work and plenty of resources available at yahoo groups GN400.
Mine is stripped of all street stuff for duty as a flat-tracker/ice bike. Here it is in summer mode:
I have a title for it. All I'd have to do is rig up some lights and a horn and I'd have a hot little city/commuter that looks like nothing else on the street. Its a "bit" loud though with the Supertrapp muffler. A 52t sprocket on the rear REALLY livens up this little beast, can lift the front wheel without a lot of effort. Longer rear shocks, with mounts moved forward on the swingarm steepened the front end for quicker steering. It's actually a fun little bike to rip around on. I bought it from a buddy set up for the ice for $800 and have maybe another $200 in parts and mods into it. Rear wheel is from a Suzuki PE400 (PE250) for the 19" tire size and the front is from a Suzuki GS650 Tempter for the same 19" tire size. A little hacksawing on the swingarm gusset makes for plenty of clearance for the ice tires and the 19" rear summer tire. Aint no lowly GN400 starter bike anymore.
When life throws you a curve,.....lean into it!
42+ year rider, 22+ year MSF Coach, Street, Dirt, Ice, ride em all!