collapse

www.cognitomoto.com

www.dimecitycycles.com

https://www.townmoto.com/collections/vanson-leathers


www.restocycle.com

www.CITYLIMITMOTO.com

www.jadusmotorcycleparts.com

www.bisonmotorsports.com

www.speedmotoco.com

www.lostapostlejewelry.com

www.sparckmoto.com

www.pistonsociety.com

www.steeltowngarage.com


Author Topic: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp  (Read 24828 times)

Offline zap2504

  • Posts: 363
Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #130 on: May 22, 2018, 13:51:54 »
Really following this with interest and I like your approach to upgrading the bike.

As you say the preload adjusters will just reduce the sag in the forks but not eliminate the mushiness in the forks, only stiffer springs will solve this.

I'm guessing the forks on the SR250 are 32mm which could open up the possibility of using RD250/350LC springs which given the racing heritage of these little bikes, springs should be readily available in a range of rates. As to what rate you require, I would guess you're looking at around 0.8kg/mm at a rough guess which Sonic Springs are listing for around $85 which I don't think is too bad. Add in the emulators and with a bit of setting up you will totally transform the bike
Yes, the SR250 forks are 32mm. But I thought the RD250/350LC forks are 34mm (E and F are 35mm)? Maybe their springs are loose like the Honda CB360/400? Maybe contact Sonic to see if their springs are less than the 23.95mm Jake measured?

Offline Pod70

  • Posts: 70
Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #131 on: May 23, 2018, 12:25:21 »
From the what I could find, the 80-83 model RD250/350 LC had 32mm forks - I certainly remember them being pretty spindly on mine all those years ago.. ;D

Offline zap2504

  • Posts: 363
Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #132 on: May 23, 2018, 13:06:14 »
I think you may be correct - found this reference - https://hvccycle.net/yamaha-rd-specs/ - that says the liquid-cooled (LC) RD350 had 32mm forks. I don't think the USA ever got that model (just the RZ350) and the air-cooled RD models (except for the RD200) look like they had 34mm forks.

Offline JadusMotorcycleParts

  • DTT SUPPORTER
  • *
  • Posts: 896
    • Jadus Motorcycle Parts
Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #133 on: Jun 19, 2018, 07:50:05 »
Thanks for all the input guys.  I will be looking into these springs for sure.  I have a couple of old fork sets on their way to me from Australia so I can use them in the development of the spacers and spring specification.

This project is going much slower than I would like - mainly due to the fact that my day job has been much more demanding recently than I thought it would be, plus I am focusing on providing the best service I can for my customers and prioritizing that over these other projects. 

I have however managed to add a video showing how to service and rebuild the SR250 carb, plus written a blog post to compliment it.  I also created a bit of a jetting guide for SR250's with various intake and exhaust set ups - share for all and report your own feedback and results!  :D :D :D



https://www.jadusmotorcycleparts.com/single-post/2018/05/17/Yamaha-SR250-carb-rebuild-maintenance-tuning

I am just as hungry as ever to get back into this project so hopefully when time becomes available it will be all on again!

Offline JadusMotorcycleParts

  • DTT SUPPORTER
  • *
  • Posts: 896
    • Jadus Motorcycle Parts
Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #134 on: Jul 28, 2018, 07:51:47 »
Finally an update worth posting...  I got around to lacing up one of the wheels this week.  I am not sure how other people do it, funnily enough I have never watched a how to vid, but I have screwed up a few times and learnt some tricks by doing.  Now that I am more confident with the process (have done around 10 wheels I guess) I think I'll make a video how to do it.  Anyone have any good tips?  Ie good youtube videos or blog posts/articles other people have done? 

I also got that package from Australia.  Most relevant to this project are the forks...  Which I can begin dissecting and experimenting with ;D Yay!

Offline zap2504

  • Posts: 363
Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #135 on: Jul 28, 2018, 11:02:48 »
I assume the Excel wheels are for the weight reduction program. If so, how much weight did you lose over OEM, and did you use the OEM size or go more narrow to reduce rolling resistance?

Offline JadusMotorcycleParts

  • DTT SUPPORTER
  • *
  • Posts: 896
    • Jadus Motorcycle Parts
Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #136 on: Jul 30, 2018, 05:04:37 »
I assume the Excel wheels are for the weight reduction program. If so, how much weight did you lose over OEM, and did you use the OEM size or go more narrow to reduce rolling resistance?

Exactly.  I will weigh an entire wheel assembly - old and new and compare once complete.  I expect weight savings to be 1-1.5kg for each wheel.  Because yes, I will be running less tyre than stock as well.  According to the rim size to tyre size charts, the stock SR rims are right on the edge of acceptable for the stock tyre sizes.  So I actually went with wider rims and narrower tyres (matching optimal sizes according to the charts) - I guess this lets the tyre perform better, or at least as the manufacturer intended.

Offline CrabsAndCylinders

  • DTT SUPPORTER
  • *
  • Posts: 1992
  • Careful With That Axe Eugene
Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #137 on: Aug 02, 2018, 23:34:16 »
I think the alloy rims alone usually save about 2.5lbs and that is reciprocal weight!
Lighter, Quicker, Faster.
ZX-14, 900F x 2, 1100F, R100, CBR600, SR500, GT500, RZ350, KZ1000 x 2, Moto Guzzi Lemans lll, CBX550, RD 350, 750 SOHC police special, RG250, TL1000R, GT750, KTM Super Duke 1290 R, Harris/Z-1, Norton 750 Commando, Green 77 KZ650

Offline JadusMotorcycleParts

  • DTT SUPPORTER
  • *
  • Posts: 896
    • Jadus Motorcycle Parts
Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #138 on: Aug 06, 2018, 12:41:17 »
I was really keen to do something fun with the project on the weekend.  Fun does not always equal the best for the project but it's a good way to keep yourself motivated and moving along.

Anyway many years ago I created a meticulous drill template for the drum brake covers/drum lever holders that I used on a project that was never finished (my Dad will get the wheels from it though!).  The template was created to allow the most drilled holes practical without messing with the structural integrity of the parts - missing all the cast details, bosses and ribs.  Which meant it needed to be scanned front and back and a pattern laid out to suit.

The process was pretty simple but time consuming.  Some might laugh at the effort but I think it looks cool and will give a special hand built touch to the bike.  I must admit, it is mostly for looks, but I weighed the parts before and after just for a laugh - a 50g weight savings!  Woohoo!  Haha.  Just gotta do that in 20 places and It'll be a kg savings total  ;D

Offline zap2504

  • Posts: 363
Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #139 on: Aug 06, 2018, 13:31:38 »
If you still have a bike with the OEM drums you could do a comparison test on braking performance improvements - especially fade.