1973 Suzuki GT250 'Robyn': cafe racing commuter

Exactly where I grabbed my crimp tool CT90

 

Mate you do realise I drew up that diagram from a 500x500 pixel uncoloured version I found on a suzuki forum?



(That's the diagram I drew it up from, and I knew what colours they used so I just had to do lots of interpreting the shitty lettering).

 

There is one way to make the generator work: replace it with a modern stator setup with electronic ignition . At €550 that'll wait a while, it comes down to properly earthing the centre of the rectifier, correctly hooking up the 'night' circuit so it charges when the headlight is on, and making sure the regulator works correctly too.

There are other options but they still result in using the pretty ordinary generator.

Diode wise that's the same as on a GT . At least I have 3 regulators and rectifiers for it in the spare parts kit, so surely one will work. That said, the diode stuff is simple enough and if it doesn't work, I can always make my own.

Alas no-one is hiding good wiring diagrams like that, I had to draw it. It's why I chucked the canberrariders and teamghettoracing urls on it, so when someone pinches it and posts it elsewhere they know where it originated from.

I actually thought the wiring diagram on Binksy's R6 was really clear. Not actually *that* many more wires, the connectors were all well thought out AND they split it up nicely into the subsections. Plus they put the original vector diagram into the PDF of the workshop manual... that's actually what mine is, you can infinitely resize it if I post an eps/pdf version of it.

Anyway it's been of great help as I match up wiring to the acewell etc. Plus I can plan out what wiring colours to buy and all that.

 

Been a big couple of days but got a lot of niggles sorted and a few more things squared away.

Last post above you can see the completed 2nd Ti fork cap. Somehow screwed the maths up on the metric-thou conversion and you need to use a different sized socket to put it on. Oh well, that's a trap for whoever rebuilds the forks anymore. Amount of care given: less than zero. It's not noticeable to the eye.

Throttle cable/quick action throttle mating
I was able to pick up a Tommaselli quick action throttle cheaply and I figured I could adapt it to the GT250 throttle cable. No real challenge, except that the cable entry on it was an M8-1.25 thread, and the GT250 stock cable uses an M10-1.25 end. I'd like to be able to use stock stuff without modifying, so, I made a little press fit adapter that screws onto the end of the stock GT cable and then presses onto the housing.



So good, I had to get a 2nd picture



Super happy with this one.

Getting the front brakes working
No real challenge here either, just add fluid and bleed. Made a little easier by the M/C bleed nipple on the Magura master cylinder I am using.



Static the lever pull feels good. It's not short but that's fine: for a bit like this, I'd prefer feel over an instantaneous level. Miles better feel than what I remember stock GT250 brake levers feeling like, too.

Mounting ignition coils
The stock GT250 coils were ok but I decided years ago that an upgrade wasn't a bad idea. These are 3 ohm coils, which are what you need for electronic ignition (which I have ready to go), or I can throw a 2 ohm resistor inline with each one and run stock points ignition.



I decided to mount the coils in the standard position, which hides under the tank and into the frame backbone. The standard ones are a touch smaller in all dimensions so these were never going to fit on the standard mount. Ended up using countersunk bolts with some little spacers I spun up on the lathe to hold them off a sheet of 3mm aluminium. The mount then bolts to the stock mount location using some nice M6 nutserts to allow you to thread it in from underneath the tank.

Plug leads and caps will be ordered soon. Got something fancy planned here.

Clutch side switchgear etc
Nothing much to report here, but it's all mounted.



Front wheel spacer to remove speedo drive
To give me enough clearance for an electronic sensor for the Acewell speedo, I needed to remove the stock mechanical speedo drive. Few minutes on the lathe and I had up a nice aluminium one. I may do one in titanium later if I feel like it.





Finished mounting battery box/oil tank
Finally sorted out a lid for the battery box. It's quite well secured really. Also used a bunch of nutserts to hold it using original frame tabs, another bonus for preserving originality within this built. (So far the only change I've made to the frame etc is to take the front footpeg mounting bolts out to M12-1.75, up from M10-1.0.





I think the lines flow rather nicely with the bike.

Front end 99% squared away now


I'm digging how it looks. Need to sort out ignition switch, indicators and electronic speedo pickup and everything forwards, or just directly above, the headstock is sorted.

Rearset shenanigans
Did a bit of playing around with peg positions and testing exhausts & looking at what sort of chambers I'd like to run post rego. Came to the conclusion that running the lowish and forwards pegs was untenable, so we hacked off some plywood to at least mount some pegs to test some thoughts.



In doing so, it became very apparent that the ideas for a gear change mechanism for the bike were going to be rather hard to implement, especially to maintain road pattern gear shifting.

I started tearing out my hair, and Charlie would have if he hadn't shaved his head, trying to come up with a solution. After dinner time, and several beers, a sensible solution was achieved. Some quick drawings, some metal fabbing and release candidate v1.0 was approved.





This contraption is a Suzuki quad bike gear shift mechanism, hacked apart, onto which some 12mm mild steel rod is welded. Then, heat is applied, and it's all bent in a few directions to make it clear stuff. Finally, heat the piss out of the end of it, smash it flat with a giant hammer, drill it, mount toe piece.

This build now with 100% more blacksmithing.

I'll wire wheel it and paint it satin black, but, success. Race pattern, admittedly, but hey, #yolo, it's a cafe racer. Feels bloody perfect with the pegs a long way back like we came up with.

So, time to replicate the measurements, make up some aluminium footpeg mounting plates, redo the rear brake rod and add brass bushings to the torque arm, job done.

Stuff to do
Lots of stuff, as always. The rearset plates are probably the biggest bit of fabbing, along with some various bits for the motor etc. I need to get some extra stuff to arrive to make up the stuff for the oil tank, plus buy a heap of various coloured wires to do up the wiring harness. Then, I can start the damned thing, and start the process of rego so I can then rip all of the road legal stuff, like the full length mudguards, off the bike.

 

After rego no.

 

Trust me, me in boots I can get my toe under to up shift, and it clears the pipes. Expansion chambers will help clearance issues but not getting me through Dickson . The amount of room is also deceptive: the toe part is outside of the centre of the exhaust, so it's got the larger clearance under it than you have under the seam of the weld. Should let the kick starter clear it all, too .

 

This is where it gets painful; if it were a later bike (post 1 July 1975) and had a compliance plate, I could get rego done anywhere and I know I could get through. But since it's not, I gotta go through Dickson and it also gets a nice simple ID check done too. However, no ADRs to adhere to including noise... I just don't feel like trying to have that argument.

(I have to meet requirements of size of mirrors, but it only needs 1, and indicators. The joys of reading the regulations. Doesn't mean they'll pass it though...)

 

That's the plan. The fronts are good - even found HH pads for it - and chasing some matching rear shoes.

Am aiming for a bunch of neat and tidy with this, too.

 

Forgot to put this up: