Pre 78 125's

[oldfart]

Bill,  Joan and I have had a few straight line drags over the years and the B motor seems to pull away in most cases..... Not by much
I agree the B motor drops off a little earlier, but it's all about the right hand and left foot combo  

[JohnnyO]

true but more power was easy to get , 34mm mik alone made a big diff, head and porting and maybe a pipe and they flew .AB won the OZ title on one in 76  with close to stock suspenders. But for sure the RM was best off the floor in 77 .

AB was second in the '76 125 title to Steve Cramer but Darryl Willoughby did win the '77 Oz title on a CR.

Jeez you're good . Anyway they were competitive in the day with some work and a good 125 pilot.At that level its all about max power , a reed valve  have less significance .

Yeah i like the CR even though i raced a RM125b in '77.
That's why i've got a Mugen kit sitting here and a '76 CR125 stripped down ready to build one day...

Is the kit complete ? What are you waiting for ?

Time is the biggest problem.. with so many projects already on the go and weekends where i'd rather go riding it takes forever to get them done.

[JohnnyO]

For me its an RM 125A  the B was a better bike in most respects but the A motor really revs 

I would probably run B forks dropped through the clamps to keep the ride height lower like a A and decent modern shocks .

When i got my brand new RM125B to replace the A i thought the B was better in every way, especially the engine with more bottom end.

[Nathan S]

Someone please say a stock yz125d with a far below average rider with above average weight is the go!!!
Please

It is, actually. Mostly because of the motor that is relatively tolerant of being asked to do something when you're in a too tall gear.
They're also physically larger than the other pre-78 jap 125s.

If I were to set out to build the fastest possible bike for the class for me, I'd start with a YZ125D. DG swingarm, modern shock internals (and modified to get 9" of travel), 250D 38mm forks, plus all of the usual motor stuff.
I know the pro-Suzuki arguments, but I firmly believe the Yamaha is the better bike for the bigger and/or less talented rider.

I've got 95% of the bits to build such a bike but haven't, because I love riding my YZ-X - and I reckon that's the bit that really matters.

[firko]

I know that there's no way I'd have an RM125B or C with an alloy swingarm. Too many train spotters out there with their parts books in their back pocket.

Being a biggish fella for most of my life I've rarely felt the need to dive into the 125 pool except for my Bully Sherpa S in 1969, Hodaka Combat Wombat in the 70's and MX125 Yammy in the early vintage days. Having said that, Jonesy and I have pooled our resources and we're building a pre 78 125 based on the Trackmaster motocross frame I got from Rob in Whyalla. It's a featherweight little Chro-mo creation already but AJ's fitted a Boyd and Stellings swingarm, we're using 36mm YZ250 X forks and front wheel, MX125 rear wheel, Ohlins shocks from a Maico, Yamaha MX125 5 speed engine with a Noguchi barrel (looking for a matching head), 34mm Mikuni, Vintage Iron pipe, YZ125X seat and tank. Neither of us have done a bike for this era before so it's all new ground. I realise that we're a bit restricted by the 5 speed MX125 motor but I was given a ute full of them so it would have been silly not to use one....plus the fact that the frame's made for that engine and all of the other parts were laying around both of our sheds. It'll be legal, trick, cheap and above all a fun little bike.
                                                                      

[Slakewell]

IMO the best looking Pre 78 125. I did look at fitting a Honda crank or even complete bottom end to make one race ready but even I'm not that much in lust.



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