collapse

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.cognitomoto.com

www.sparckmoto.com

www.Moto-Madness.com

www.pistonsociety.com

www.steeltowngarage.com


Author Topic: 250 Single - Performance Upgrades  (Read 1369 times)

Offline crazypj

  • Posts: 13157
  • Split personality, I fake being smart
Re: 250 Single - Performance Upgrades
« Reply #20 on: Jun 01, 2018, 11:00:53 »
It would be more difficult to make but a long reverse cone megga would be far better than any 'shotgun' style system.Parallel pipes are best for max power over a very very narrow rpm range (as little as 500rpm in my experience)
'you can take my word for it or argue until you find out I'm right'
Best thing I ever overheard
"yep, PJ's my boss, he taught me everything I know, just didn't teach me everything he knows"
Brian Morgan, 1982

CB360's,  http://www.dotheton.com/forum/index.php?topic=11736.0
XS650,  http://www.dotheton.com/forum/index.php?topic=11922.0

Offline paddyshepherd

  • Posts: 59
Re: 250 Single - Performance Upgrades
« Reply #21 on: Jun 01, 2018, 15:19:24 »
Hmm, possibly. I know reverse cone megas have always been the done thing on caffs and are good for power but I've never really been that keen. My other option is have an upswept pipe either side that matches the lines of the frame 🤔

Offline crazypj

  • Posts: 13157
  • Split personality, I fake being smart
Re: 250 Single - Performance Upgrades
« Reply #22 on: Jun 01, 2018, 18:38:44 »
Yeah, it's always been difficult to find one that looks good and still works. Gold Star style would be different but damn difficult to make unless you could find a bottle with right diameter (rolling cones isn't too difficult after you've done the development)
'you can take my word for it or argue until you find out I'm right'
Best thing I ever overheard
"yep, PJ's my boss, he taught me everything I know, just didn't teach me everything he knows"
Brian Morgan, 1982

CB360's,  http://www.dotheton.com/forum/index.php?topic=11736.0
XS650,  http://www.dotheton.com/forum/index.php?topic=11922.0

Offline paddyshepherd

  • Posts: 59
Re: 250 Single - Performance Upgrades
« Reply #23 on: Jun 02, 2018, 14:03:14 »
Yeah, I agree cones are nice and simple in that sense.
I have however just realised that upswept may not be so easy for me, since my rearsets are going to sit so far back on the bike. I may have to just run underslung pipes.

Offline paddyshepherd

  • Posts: 59
Re: 250 Single - Performance Upgrades
« Reply #24 on: Jun 06, 2018, 08:54:10 »
I'm wondering if an oil cooler may be a worthwhile addition, if there is a suitable oilway that I can pick up from and return to. I know kits used to be available that mounted where the starter was on the normal cb250's, but I've not seen anything of the sort for an RS, so I'd probably have to use a universal cooler.

Offline crazypj

  • Posts: 13157
  • Split personality, I fake being smart
Re: 250 Single - Performance Upgrades
« Reply #25 on: Jun 06, 2018, 11:11:05 »
If you have service manual with oil flow diagram it should be relatively simple to find oilway on/in clutch cover or crankcase to tap into. If not, you have to figure out oil flow from the castings which csan be much more difficult. RS motor has pretty long cases though so you have more surface area to help keep oil cooler, it may not be needed?
'you can take my word for it or argue until you find out I'm right'
Best thing I ever overheard
"yep, PJ's my boss, he taught me everything I know, just didn't teach me everything he knows"
Brian Morgan, 1982

CB360's,  http://www.dotheton.com/forum/index.php?topic=11736.0
XS650,  http://www.dotheton.com/forum/index.php?topic=11922.0

Offline paddyshepherd

  • Posts: 59
Re: 250 Single - Performance Upgrades
« Reply #26 on: Jun 08, 2018, 04:39:39 »
If you have service manual with oil flow diagram it should be relatively simple to find oilway on/in clutch cover or crankcase to tap into. If not, you have to figure out oil flow from the castings which csan be much more difficult. RS motor has pretty long cases though so you have more surface area to help keep oil cooler, it may not be needed?

I have a manual but not sure if it's got that kind of info. Will have a check tonight.

I've narrowed my carb options down to a Keihin CR33, or possibly the Mikuni TMR32 (there's a fancy yoshimura version of that, too). The F-CR version of the Keihin I think will be too tall, and is definitely more a race carb without the choke. The TMR, despite being a similar beast, has a choke. The benefit to the TM series is that I can get it as a pumper carb whereas the CR I can't. The TMR32 is, granted, smaller than the stock carb, however from my logic being a mechanical carb rather than a CV it should flow much better and still be an upgrade. They do however also offer a 34mm, but I think that might be overcarbing the engine by quite a bit.

Offline crazypj

  • Posts: 13157
  • Split personality, I fake being smart
Re: 250 Single - Performance Upgrades
« Reply #27 on: Jun 08, 2018, 11:22:09 »
33mm 'flat slide, smooth bore' will flow way more than a 32 (and probably 34mm) conventional CV carb. You will probably be way better off with a 31mm or even a 29mm as even the smallest one will flow at least as much as the CV on there now. Your right about having accelerator pump, it will let engine pick up much quicker. You may need to change metering jet for it though and possibly limit pump stroke
'you can take my word for it or argue until you find out I'm right'
Best thing I ever overheard
"yep, PJ's my boss, he taught me everything I know, just didn't teach me everything he knows"
Brian Morgan, 1982

CB360's,  http://www.dotheton.com/forum/index.php?topic=11736.0
XS650,  http://www.dotheton.com/forum/index.php?topic=11922.0

Offline paddyshepherd

  • Posts: 59
Re: 250 Single - Performance Upgrades
« Reply #28 on: Jun 08, 2018, 13:36:37 »
33mm 'flat slide, smooth bore' will flow way more than a 32 (and probably 34mm) conventional CV carb. You will probably be way better off with a 31mm or even a 29mm as even the smallest one will flow at least as much as the CV on there now. Your right about having accelerator pump, it will let engine pick up much quicker. You may need to change metering jet for it though and possibly limit pump stroke

Pretty much what I thought PJ. However, what's odd is that when I'm looking online at the yoshi' Mikunis and the Keihin Kits, it doesn't seem to match that logic. The smallest Keihins in either flat or round slide both spec 33mm for the RS, with a 35mm kit also available.

Yoshi don't specifically do a mikuni for the RS, but do one for the XR250. Which believe it or not, is a 34mm TMR Flatslide with their MJN (from what I gather, their MJN relieves the need for mega accuracy on the main jet as it's apparently good for multiple engines). They also do a TMR32 and 28 in the same spec, but they quote these as being for bikes such as the NSF100 and various 125cc bikes.

Weird.


Offline crazypj

  • Posts: 13157
  • Split personality, I fake being smart
Re: 250 Single - Performance Upgrades
« Reply #29 on: Jun 08, 2018, 14:51:57 »
Is the carb information from Mikuni site or from a retailer?I got info direct from Mikuni on the VM's, only bit I can remember off top of my head is VM32 will support 50bhp per cylinder.
If you work out various throat sizes, a 36mm has almost double the area compared to a 26mm carb with a corresponding reduction in flow velocity. May be OK for a bike that rarely sees less than 6,000rpm but would probably be pretty horrible around town  ;)
'you can take my word for it or argue until you find out I'm right'
Best thing I ever overheard
"yep, PJ's my boss, he taught me everything I know, just didn't teach me everything he knows"
Brian Morgan, 1982

CB360's,  http://www.dotheton.com/forum/index.php?topic=11736.0
XS650,  http://www.dotheton.com/forum/index.php?topic=11922.0