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Author Topic: 250 Single - Performance Upgrades  (Read 1491 times)

Offline paddyshepherd

  • Posts: 71
Re: 250 Single - Performance Upgrades
« Reply #30 on: Jun 08, 2018, 16:20:45 »
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  ;)

Well, the info is shown on the retailers website, but I believe its Yoshi/Mikuni that are stating the fitment - they're supplied as a kit, with the correct spigot etc to fit certain bikes. I believe they also come with "somewhere near" jetting, the same as the BITO R&D Versions of the Keihin carbs.

Offline paddyshepherd

  • Posts: 71
Re: 250 Single - Performance Upgrades
« Reply #31 on: Jun 14, 2018, 14:51:39 »
Well, I've decided I'm going to pull the engine right to bits, purely because I want to get it all blasted so as it's halfway stripped I may as well go the whole hog. Cam is going off to Newman Cams tomorrow to have a "fast road" grind. I'll get the higher comp piston but I'm unsure as to whether or not I'll go for a big bore as of yet. Still deliberating over carb choice. Exhaust I'm not worried about for now as that'll be one of the last bits I sort, and it'll be a custom fab job anyway.

Offline paddyshepherd

  • Posts: 71
Re: 250 Single - Performance Upgrades
« Reply #32 on: Jun 15, 2018, 16:05:00 »
I also found out yesterday that apparently the Keihin PD70 is not a CV carb like I previously believed. I assumed that it was due to having a quick look at it off the bike and seeing a butterfly valve. Turns out that when it's all hooked up that's just the choke, in my limited experience with carbs I'd not come across that as it's apparently the older way of doing it. Still, it'll be quite a restriction. I'm swaying towards the standard Mikuni TM33 Pumper, as I can get that in the UK and it'll have better support if I need advice. Finding anyone over here that knows much about the Yoshimura MJN system is proving difficult, so I wouldn't have much to go on if I did run into problems. Having said that, it's claimed that the MJN is easier to set up than a standard carb.