Topic: "hot" parts for a honda 125?

[jaguar]

im looking for some race parts for a 74 CB125.  i know that there were a bunch of cool things for the SL/XL125s and those parts will fit.  if you have any lines on where to get parts please let me know

[oconnor]

I know the 125 twins had hop up parts but I've never seen anything for the dingle. Which are we talking about?

[crazypj]

Modify a CB750 piston and you can fit it to get 145cc.
Depending on cam bearings you may be able to get XR185/200 cam or have yours re-profiled to different spec(XR200?)
PJ

[jaguar]

im doing some landspeed racing at maxton and it needs to stay 125cc
its for a single

[333]

Megacycle Cams for a start.  There is someone else that I forget, I'll ask on Tuesday when I visit the shop I used to work at.

[gregwaits]

Back in '72 or '73, Dirt Bike magazine had an issue that was devoted to hopping up the SL100/125. At the time I had an SL100 and was forbidden from riding on the street (mom's do that after you have an accident involving a car!).

The articles were very thorough. If you could track down the year and month and get a copy, it would give you great ideas.

I wanted to trick out my SL the way they did the one in the magazine, but my allowance didn't go too far at the time. I couldn't afford the aluminum frame and rims or the magneto system. All I could pull off was the Basani open header pipe.

[Sam Green Racing]

im doing some landspeed racing at maxton and it needs to stay 125cc
its for a single

I have been watching this thread and have been looking around to see if i could come up with anything. Apart from the Megacycle cam, I didn't find anything but I do know that tuning parts was made for this bike.
Why did you want to use this particular model in the first place ? Is there a class for vintage/classic bikes or do you just want to find out how fast you can get this bike to go ?
I have been doing this sort of racing for 40 years useing little Hondas in the 175cc class and find it fascinating the speeds these small bikes can achieve.
Keep us posted.

Sam.

[crazypj]

 I've had a bit of a think about this and remembered one thing we used to do 'back in the day'
 Fit the left carb from a GT250 Suzuki (only one choke/enrichener and cross over tube)
 Loose a litle botom end (but it didn't have much anyway )
 The gain at top end is more than worth it.
 You can probably get a 22/23/24mm carb pretty easy, just have to work out jetting, Mikuni use a different system to Kei-Hin ( flow in cc compared to actual hole size)
 We had XL125's doing indicated 85/90 (95 with a tail wind, but capable of 60/65 pretty much everywhere)
 PJ

[flatblack]

Check out these guys:

http://www.powroll.com/

HTH...

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[jaguar]

powroll has been helpful
i plan to run at maxton.  they have a 4 stroke 125cc class and the record is in the mid 60mph.  i know i cant beat a 2 stroke 125 but should be able to top a 60mph record
ok i should have started with what i have...
i have a 26mm carb
high compression domed piston
2mm over sized valves
17t front 35t rear( to start)
plan to have the head ported and polished.
the proplem im having is getting race vlaves and springs and also a neddle bearing cam.  ive found a ton of old dirt bike articals but cant get the top end done. 

[333]

I had a bone stock '80 CB125S that would do close to 70.  It would take a while to get there, but...

[jaguar]

im looking for 100mph out of it

[flatblack]

im looking for 100mph out of it

I don't see why you can't get there from here.  Hell, some fairings and a gearing change on a stock CB125 should get you to around 80-85...

Keep us posted, wilya?

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[jaguar]

found this guy in asustraila that makes custom cams and SS vavles.  i have to figure a time in the middle of the night here to call him....lol

[Sam Green Racing]

Just out of intrest, what do you weigh suited up, ready to ride ?

Sam.

[jaguar]

i honestly dont know.  im about 190lbs.
i should weigh more then the bike when its done

[Sam Green Racing]

You nearly do now ... bike weighs in at 194lbs dry.

You'll need to shed about 50lb if you want to get anywhere near 100mph

Good luck.

Sam

[jaguar]

im sure that you know how to figure this alot better then i do but how did you come up with that? 
me on a stocker did and indicated 65-70.  thats about 13hp.  im figuring the new motor to be in the 19 range.  add gears, lightness(i dont think the bike can lose 50lb) and a fairing and i thought i would be close

[Sam Green Racing]

Hi Jag, I have been looking at the specs for the CB125s and find that the weight of the bike varies a little from spec sheet to spec sheet, so lets assume an average weight of 200lbs.
I don't know if you have started work on the bike yet but you should be able to get 50lbs off it quite easily, what made you think you couldn't ? Let me know what you are doing to lighten the bike.

Getting the bike to produce 19bhp might be a little optimistic but I am no expert on this particular engine, I do remember however that these little motors got up to top speed quite quickly with the very nice 5 speed box. I was a Honda tech when they first came out and it was my job to build the bikes from the crate and get them ready for the road, I remember the first one I tested, I was quite impressed. whatever you do with the motor, the more you can get from it the better.

I probably don't need to tell you, getting the maximum speed from a bike is down to 3 basic things. Power, weight and streamlining.
A lot of people think that reducing the weight of a bike and its rider only makes it accelerate quicker, it doesn't. Because you are pulling less weight it allows you to pull much higher gearing and this is were the extra speed over the stock bike comes in.

Basically, if you can shed the same amount off your body as you can off the bike (50lbs) with the increased engine power and a decent streamlining you might be in with a shout.

Keep me informed of how you are doing and I'll do my best to offer advise where I can.

Sam.

[crazypj]

found this guy in asustraila that makes custom cams and SS vavles.  i have to figure a time in the middle of the night here to call him....lol

Depending on the sizes you want, you may find titanium valves from a new 4 valve head to fit (just get some valve guides made for different stem sizes)
I didnt think of this, a friend was going to fit Hayabusa valves into a CB350 but heads are smaller diameter than 350 ones.
 If you have lighter valves you wont need heavier springs so will reduce parasitic power loss.
 I'll see if I can come up with some numbers.
PJ

[jaguar]

^that would be great i could use all the help i can get

[jaguar]

had a few pic to show you guys. 
still working out the motor....got a spare 100cc in there for now.  still need to mount the seat and make lower shock mounts too.

[crazypj]

im sure that you know how to figure this alot better then i do but how did you come up with that? 
me on a stocker did and indicated 65-70.  thats about 13hp.  im figuring the new motor to be in the 19 range.  add gears, lightness(i dont think the bike can lose 50lb) and a fairing and i thought i would be close

 They only made about 8~9bhp at the wheel.
Best modified XR200 I've seen made 23.8bhp@ 12,500 (then the rod broke, Wiseco piston is a lot heavier than stock)
 19 from a 125 is probably asking a bit much, even if you rev it to 15,000.(may be possible with lighter piston though)
I think about 15~16 will be realistic (but I would be interested if you get more)
 KTM 125 MX ( two stroke) puts out about 34 bhp on same dyno
 You should be able to shed at least 35~40 lbs from bike, lights, mudguards, small seat and tank, lighter exhaust, cut of any brackets you don't need etc
You want to cut those bars down to the narrowest width you can mange (about 2" narrower than your shoulders overall width) and slide forks up a bit (or cut springs down, you only need an inch or two suspension both ends)
 Make up some rearsets and hang them off swing arm pivot, then you can get rid of huge heavy brake pedal.
 Look for some moped wheels,(or S90?) narrower tyres will have less rolling resistance (and use narrower drive chain)
 watch 'Worlds Fastest Indian' again, low and narrow
 It doesn't have to be street legal does it?
PJ

[mlinder]

the racing 160's here, faired, do about 85mph in a draft around PIR.
Good luck getting 100

[jaguar]

nope t doesnt have to be street legal...would like it to be though....just for fun
was thinking about excel rims.