RM125S 1975 Resto - questions

[Mark Austin]

Hi lads,

I've been making some progress on my RM125S resto, I recently recieved a lot of parts from overseas, so today was spent putting bits and pieces together.
The bike was in boxes, so there are some parts missing, and some are incorrect.
So I now have:
A TM125 tank on the way - needs to be painted
1 wheel rebuilt, next to be done tomorrow
Seat cover to be fitted tomorrow
Rear shocks (thanks Graeme M)
Good front forks -  non rusty fork inners from a DR250 for $20.00 (thanks Doc)
Rear axle and various other bits .
Handlebars, controls and cables
The motor was checked and didn't need any work
Opaque white guards and side covers on the way

But I have a couple of issues:
It has the wrong carby on it - it has a larger (in size) 32 mm carby on it, that doesn't really fit the space, as it hits the CDI, and there's not enough room for both.
Does anyone here know the specs for the correct physical size 34mm Mikuni, I don't mind buying a new one, as they are pretty reasonable in price now.

Does anyone have a suggestion as to the correct approach, I think I have a starting point for jetting for the 34mm carby, as Graeme M listed jetting specs some time ago.

Any suggestions lads?

Cheers,
Mark

[Graeme M]

Mark this may help (Just scroll down the page):

http://www.suzukicycles.org/RM-RMX-series/index.html?RM125_1975-1980.shtml~isoraami

Gives carb jetting and claims the CDI was mounted on the headstock. I'll assume it was an M frame with an extra bracket added...

[DR]

yeah, the S had the cdi relocated because of the carb being further back. Preety sure I run a 32mm on my S engine and it fairly flies. Unsure what the carb is but it's an older high top type from a vintage snowmobile whatever it is, it worked perfectly from the moment it was bolted on in hindsight I should have looked further as there probably would have been a pair of them listed even has a powerjet system cast in but not drilled or connected.

[oldyzman]

Mark,
The 34 mm goes very close to the crankcase. I can tell you the jetting spec that mine has if you need it. My S seemed to be losing low down power more and more, i foundit was sucking air from between the cyl and the alum carby mount. Once i improved this it seemed better. I cannot help wondering if the 32 is a better size for it though. I have read a book on two stroke tuning and it talks about having 2 more HP right at the topend at the top end but losing so much through the low and mid range that its not really beneficial. Does your one have any sort of reed valve feeding to the crankcase, kind of like the A...
Cheers Brett

[Mark Austin]

Small setback - I started to put the rear wheel together and noticed a crack where the manufacturing joint is, and as I now have the front end in, I checked the frame for straightness, and its bent at the back subframe - bugger.
Oh well back to the drawing board.
Cheers,
Mark

[Lozza]

I would be running the 32mm carb FWIW

[DR]

Have ridden both and find the 32 is a better thing, I didn't notice any difference up top but midrange and what there is at bottom end was improved and much more user friendly. It actually has some roll on now which never existed before not to be confused with run on which is my pet hate