Suzuki GN125 | First build

[TijmenK]

It was nice for as long as it lasted. :'( Made it to the gate of the backyard before she died on me, the battery is fried so no big deal but I just wanted to get out and ride. I cut the battery short a week back, some hissing and quite a bit of smoke later it still seemed to work. I also was able to charge it then and I could test and star, but now it doesn't take any charge from my battery charger anymore (0.5 amp out of the 3 amp it can give) and doesn't give out any to the bike either. Everything works when the wiring is directly attached to the charger so that's ruled out too.


Any advice on battery choice? There's currently a 9 ah gel battery in it, the Haynes manual specifies 7 so I'm not sure why the PO put a 9 in it. Currently there's a German gel accu in it I can't buy anywhere near me, I want to mount it under an angle so I'll have to go either gel or Li-ion. I think I'll go for a Motobatt because there's a dude near me who stocks them and they're getting pretty good reviews.

 

[TijmenK]

Slowly making progress, made it to the corner of the street before I discovered my horn / taillight / indicators didn't work, turns out butt connectors are a shitty replacement for a proper connection with bullets. But she rides, brakes, shifts and has a pretty cool grumble, so I've got that going for me.

 

[TijmenK]

Wooh, first ride is a fact. It runs like ass, as expected. Only changed the main jet for the new filter, starts with choke but quickly dies when stationary and lacks power under 5000 RPM. Got some good info on my carb so it should work out.


The new battery is a couple of mm too big for the current battery box but I wanted to do a new one anyway. I want to have my ignition, CDI and flashing relay in there too which should make for a much cleaner rear triangle. Which will make jetting much more enjoyable because it gives me way more space than what I have now:

 

[TijmenK]

Took it apart and put it back together again, much neater and will make it infinitely easier to jet the carbs because it was a bitch to get out. Made a new battery box, currently at the welder which is taking some time. Learning to weld is top priority as soon as the bike as it's running again. Got an unexpected $1000 from the insurance of the rider who rear-ended me on my bicycle nearly a year ago, so that will definitely help with getting some tools.

 

[TijmenK]

Left to do:

• Drill holes for mounting the new box.
• Clamp leads to the new battery cables.
• Mount fender to the battery box.
• Turn the pilot jet until it starts without choke.
• Lower the needle clip until it runs nicely.
• Ride.

 

[TijmenK]

;D

 

[bgolding]

Loving the build Tijmen, I'm thinking about starting up my first build on one of these Japanese 125s.

 

[TijmenK]

Major thread dredge!

The poor thing has been rusting in the backyard for the last couple months, time to get it on the road again before spring! I kinda forgot how shitty it was when I put it away so making a to-do list was confronting.

• Fix wiring for once and for all, I ordered new battery cables and a proper crimping tool, still have to decide on the terminals. This includes properly mounting the CDI, start relay and all that jazz.
• Fixing the miraculous 7k RPM limit, I was able to get a new CDI for cheap so I'm going to install that and hope that will fix it.
• Fixing the shifting linkage, currently have a bent piece of threaded rod, not very trustworthy.
• Fix everything between the rear-wheel and the tank, the seat doesn't fit and the battery box and rear funder suck. I think the only thing I'll reuse is the leather cover of the seat, I'm gonna fiberglass a new cowl and integrate all the electronics in it and make sure it leaves clearance for the fender. I'm think of getting something like this and mounting it to the rear bridge instead of the frame.
• There's no pressure in the front brake anymore, doesn't have priority but I'll take a look at it.
• Fix the mounting of the exhaust and make a rubber stop for the centerstand.

And a pic, to show the gravity of the situation:

 

[jeffcampagna]

Loving this build, Tijmen!!

And thank you so much for the great info and play-by-play. I've got a Suzuki GN 125 down in Panama that I've fooled around with. Gave it a sort of poor man's vintage Triumph look (see attachment). But now I'm hoping to change it to a more cafe racer style. (lower front forks, raise back of fuel tank, exhaust wrap, clubmans, low profile seat with a DCC rear hoop, striped tank etc...)

Big change will be the seat. Your new seat is incredible. I sent you a message about it.

 

[TijmenK]

Thanks for the kind words Jeff, I've replied to your PM, a tad late but I hope it was of help!

This time I'm going to start working on it for real. I've got new mirrors, bar controls, speedometer. I have stripped the entire wiring loom (again :-\ ) and want to do it properly this time around.

Next to that I'll be working on all the bodywork behind the tank, so seat, electronics tray, rear fender and mounts for the lights and plate.

When that's done it should be riding and road legal again,

 

[jeffcampagna]

Thanks Tijmen! I did get your PM. I appreciate the drawing you included.

I also wanted to ask, when you switched to your dad's XS650 muffler, did you take his header as well? Or just cap your 125 header with the XS650 muffler? The reason I ask is because in the latest shot, with the black wrap, the header seems to be shooting back with a straight line under the rearset instead of the awkward 125 exhaust upswing. (does this make any sense?)

Anyways, good luck with the rest of the work!

 

[TijmenK]

Thanks Tijmen! I did get your PM. I appreciate the drawing you included.

I also wanted to ask, when you switched to your dad's XS650 muffler, did you take his header as well? Or just cap your 125 header with the XS650 muffler? The reason I ask is because in the latest shot, with the black wrap, the header seems to be shooting back with a straight line under the rearset instead of the awkward 125 exhaust upswing. (does this make any sense?)

Anyways, good luck with the rest of the work!

I used the original header, chopped it off just before the last bend and welded on a small piece of bigger-diameter tubing. The GN125 header is tiny (35mm from the top of my head) and most aftermarket exhausts take ~45mm, which can be reduced to ~38mm with spacers.


Finally started work on this again, nothing much to do in the coming two months so it should be finished right on time for the end of summer. :-\


I want to start at the front and work towards the seat, so first thing on my to-do list is the dashboard. Did all of it with a hand-held drill, some hole-saws, a hand-saw and a powerfile. Still a bit rough around the edges, but mostly finished. I made this out of 2mm sheet alu, which is sturdy enough. I also have a piece of 4mm sheet to make it less "scrawny", but I think I'll just keep this for now.

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[jeffcampagna]

Dash looks cool Tijmen.

Thanks for the tips about the exhaust.

Hey, I was wondering, how did the whole rejet go? I'm looking to put a K&N pod on my GN125 and was thinking you might have some advice. Did you ever get this bike running smooth as stock?