Question about the suzuki GN 400

[Dizzixx]

I understand it's not a GS but I was unsure of who else to ask that I thought you guys might know.

So my friend bought an 81' GN 400 as his learner bike. I rode it once and fell in love with it. I am no stranger to the wickedly fast, uber nimble, or old school style. I have had or have a 99' Bandit 1200 S with all kinds of goodies, 92' Bandit 400 pure stock my first bike, and my current 77' GS 750 with wiseco 2mm over (to 850cc) as well as dyna s ign and other stuff.

But this GN is something special, something about the feel of it is just awesome. My aforementioned friend managed to throw his up the road and I have been helping him fix it, he just bought 3 parts bikes for a killer deal. I was thinking of buying one and turning it into a cheap bobber or something.

So I would like to know is it at all possible to build up the little thumper single? I searched google, ebay, etc and couldnt find anything in the way of a bore kit for this specific application so I was wondering if someone knew of a junkyard find, piston wise, that would swap in and accomplish the same end.

Stock the GN 400 (which should be the same as the SP and DR of the same vintage) is a bore and stroke of 88.0 x 65.2 mm (3.5 x 2.6 inches). What about doing something carb wise? cv maybe, or along the lines of port and polish the top end? Anyone have any experience with something like this? I dont expect to get much out of it, but it buzzes and feels like its straining to do 65-70mph on the freeway, it would be nice to just get a little extra out of the top end. I would also be open to a chain conversion with sprockets to aid in accomplishing the same end.

Any info would be greatly appreciated.

[atchbo]

Whoa. That's a one-lung thumper? Cool. I don't have any solutions necessarily but you might want to look into replacement parts for the old Royal Enfields. I guess it's unlikely the wrist pin will be metric, but it might give you some ideas. And you can buy aftermarket Amal or Mikuni carbs for those (likely VM) that will likely be easier to deal with. I dunno.

Free up the exhaust, put a K&N or other pod/cone filter on it, and feed it as much gas as it will take. I doubt the head porting will help much, but I've never tried. A bigger bore/stroke might though, and if you bring in the piston, a machine shop might be able to help you find a suitable piston. My 2c.

[LeeGS550E]

I still have my GN400, but its been dead since a friend of mine crunched it in an intersection. I bought it from the original owner and rode it for about 4 years.

Like you say, its a pretty buzzy little bike. Fastest I ever got mine was 82 mph. It will run on the highway, but its better for around town and backroads.

I didn't do any tweaking on mine, but I think your best bet would be finding parts that crossover from the DR series. I believe the DR shares the same engine. Pretty sure Suzuki's thought was "Lets just put the DR motor in a streetbike frame". So you could probably look for DR parts.

Pipe it for good sound, put a pod filter on the carb, jet it, and away you go!

I did 13 o'clock mine once - the little thumper has minimal power, but good torque.