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Mikuni VM - 2 stroke/4 stroke differences... #205268
12/19/06 2:38 pm
12/19/06 2:38 pm
Joined: Jun 2004
Posts: 1,115
Kansas
kboyd Offline OP
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kboyd  Offline OP
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Joined: Jun 2004
Posts: 1,115
Kansas
Just wanting to confirm what I think the Mik VM Super Tuning manual says (section 3-2-2)....

The only physical difference in the 2 stroke or 4 stroke carbs is the needle jet?

4 stroke (bleed type) needle jet having holes drilled for air from the air jet to be metered by the needle jet/needle.

Other than that, are there any physical differences that would require attention before converting a 2-stroke Mik for use on a 4-stroke?

Thanks for any help,
Kyle


Kyle#44x

1969 T100R Daytona
1979 Powroll Honda XR250 "Dallas Baker" flattracker
1975 XL350 project bike
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Re: Mikuni VM - 2 stroke/4 stroke differences... #205269
12/19/06 3:06 pm
12/19/06 3:06 pm

A
Anonymous
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Anonymous
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A



The 2-stroke Type 159 (primary) needle jet is standard for most 4-stroke twins using the VM 30, 32, 34, 36mm. The bleed type doesn't appear to offer any advantage, and not only will it need larger sizes than the 159 but also affects needle taper.
Watch out for extremely rich jet sizes, and anything used on snowmobile or PWC will have a small needle and seat assembly - must be changed to 3.0 minimum.

Re: Mikuni VM - 2 stroke/4 stroke differences... #205270
12/19/06 3:46 pm
12/19/06 3:46 pm
Joined: Jun 2004
Posts: 1,115
Kansas
kboyd Offline OP
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kboyd  Offline OP
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Joined: Jun 2004
Posts: 1,115
Kansas
Thanks Panic. I have a pair of "like new" vm28's from a Yamaha Banshee that I was looking to convert for my Triumph 500.

Thanks for the info!

Kyle


Kyle#44x

1969 T100R Daytona
1979 Powroll Honda XR250 "Dallas Baker" flattracker
1975 XL350 project bike
Re: Mikuni VM - 2 stroke/4 stroke differences... #205271
12/19/06 3:57 pm
12/19/06 3:57 pm

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Anonymous
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Anonymous
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The 28 has slightly different parts. The Yamaha may use its own proprietary stuff, but the generic 28 has the VM30/38 Type 169 primary type (looks like the Norton 850 spray tube on top), the bleed type alternate is Type 175.

Re: Mikuni VM - 2 stroke/4 stroke differences... #205272
12/19/06 4:41 pm
12/19/06 4:41 pm
Joined: Jun 2004
Posts: 1,115
Kansas
kboyd Offline OP
BritBike Forum member
kboyd  Offline OP
BritBike Forum member

Joined: Jun 2004
Posts: 1,115
Kansas
Thanks Panic. I don't know if they are stock Yamaha carbs or generic VM's. Looking down the mouth of the carb the spray tube looked different than a generic vm30 I used to have. It seems much more prominent.

The guy I bought them from may have changed things a bit, as they have aftermarket (Vito's?) needles and such. One of the other carbs that came in the lot was outfitted for alcohol and two nitrous jets. Not that I have a use for it... eek

Thanks again for the info, I'll double-check everything installed,
Kyle


Kyle#44x

1969 T100R Daytona
1979 Powroll Honda XR250 "Dallas Baker" flattracker
1975 XL350 project bike

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