RM125 big bore.

[bigk]

Hello Suzuki guru's,
I have decided to build a big bore RM125B for a colleague to race pre '78 all powers just for the exercise, but mainly to use up some of the spares I have. We have everything pretty much soughted and while I don't particularly want to divulge exactly what we're doing, I wouldn't mind some leads towards RM specific porting specs. Any leads much appreciated.
Cheers,
K

[lukeb1961]

http://cid-407d7ef0965d3991.skydrive.live.com/browse.aspx/Racing%20Model/RM125B

read the RM125B Owners Manual, see page 26 for the port timing diagram.
Or are you after something more?

[bigk]

Thanks Luke, but looking more for some hot up tips. We have a fair idea on what's needed but happy to have some direction from any Suzuki people who have done similar.
Cheers,
K

[monaro308]

If you are into down loading stuff ,search for.....2 stroke Performance Tuning in Theory & Practice 2 stroke and 4 stroke  by Graham Bell
There was alot of info on 2 stroke mods of that era....RM125C,PE175 and YZ80 and alot more.
Its about a 45mb d/load on Mininova.org...type in "2 stroke" in the search section

[Lozza]

Make the carb and ports match the pipe and the ignition. There you go.

[oldyzman]

Hey Lozza, How much combustion chamber volume would you start at with this project, as i have been colecting some parts to do something similar
OLDYZMAN

[motomaniac]

Hello Suzuki guru's,
I have decided to build a big bore RM125B for a colleague to race pre '78 all powers just for the exercise, but mainly to use up some of the spares I have. We have everything pretty much soughted and while I don't particularly want to divulge exactly what we're doing, I wouldn't mind some leads towards RM specific porting specs. Any leads much appreciated.
Cheers,
K

Mick ,I had a great feature in an old ADB mag.I think I sold it on ebay to Alan Riha.You can easily mod the B barrel to C specs for a start.Try and find a trick case reed valve - they come up on ebay now and then or you can mod the stockie to have petals on both sides. Frank Pons did the mods on the ADB bike as per the norm in those days.

Haven't got a spare 390 motor have you?

[LWC82PE]

my guess, TS185 or PE 175 piston or top end.
I have 78 RH250 port specs if thats any good.

i know i have that ADB article but i cant find it easily. if someone can show me the cover of that issue i can find it.

[TT5 Matt]

why not start with a pe175c/n motor and put a 2mm over 185 piston in it along with the rm125 box and maggie,then port the fork out of the barrel to improve the breathing that should get it going

[Lozza]

Depends on fuel, rpm and ignition YZ man

[lukeb1961]

If you are into down loading stuff ,search for.....2 stroke Performance Tuning in Theory & Practice 2 stroke and 4 stroke  by Graham Bell
There was alot of info on 2 stroke mods of that era....RM125C,PE175 and YZ80 and alot more.

all available here:
http://cid-407d7ef0965d3991.skydrive.live.com/browse.aspx/Racing%20Model/Two-Stroke%20Manuals

[lukeb1961]

why not start with a pe175c/n motor and put a 2mm over 185 piston in it along with the rm125 box and maggie,then port the fork out of the barrel to improve the breathing that should get it going

64mm PE175C/N Wiseco piston would be a better start, surely?

[Lozza]

It's highly unlikely you would be using a 64mm piston in an RM bottom end, unless you can jam a 21mm OD small end bearing into an 18mm OD rod eye somehow.You could swap a rod but you will be moving to a 110mm rod from a 100mm. Ports don't improve breathing ducts,pipes and carburetors do that job. 
58mm is the biggest piston with a 14mm pin so a 58 X54 will be 142cc.

[bigk]

Thanks all, lots of info there. Will keep you posted on the progress. Do you mean Husky 390 engine Brent?
Cheers,
K

[motomaniac]

[quote author=LWC82PE link=topic=9031.msg88552#msg88552 date=1249651013

i know i have that ADB article but i cant find it easily. if someone can show me the cover of that issue i can find it.
[/quote]
Hey Leith maybe it was you that bought the mag of me - I remember you won quite a few.
Its pretty easy to find since they only did 4 per year in those days.It would be 78.