The Mosquito!

I'm just getting started on this one, but here's the plan...

After getting a FREE KZ250, I found a titled frame and decided to build a stripped down, bare bones cafe' bike. Old school, 250cc Thumper. Clip on's or low Clubman bars, minimal wiring and lights, drum brakes, skinny tires, etc.
The old girl only has 19hp, but at less than 300 lbs from the factory, I figure I can strip this thing down to closer to 250lbs.

I did some research and found out that it's a 1980. I've got to pull the head and free up the piston, but the '78-79 KZ1000's share pistons with this bike and overbores are available.
Looking inside the clutch side, everything looks really nice and the bike only has a little over 4,000 miles on it.

Here's the ugly "before" pic:


And here's a little inspiration. I "believe" it's a Wards/Riverside or Benelli from the late '50's to early '60's. I snapped theses pics in the swap meet at Barber this year.

Excellent...keep those pictures coming...we love photo essays.

Here's the vicious powerplant. One fourth of the mighty KZ1000!
I've also determined that the carb isn't stock. It's a Mikuni round bore; no vacuum diaphragm. I haven't figured out what size it is or what it's from, but the P.O. had electrical tape wrapped around the throat to make it fit the manifold. Yeah, I'll have to do something about that.
But the velocity stack must add 2HP!

Now, just use your imagination....


Or maybe something like this?

I think the last one is actually a KZ250 twin, but you get the idea.
I wonder how I can tell what carb I have? There are no numbers on it. If I measure the throat and/or slide diameter, think I can find out?

Looks like a Mikuni VM series. Measure the inside diam of the (engine side) bore. Great project, looks like a fun one.

RLB454 wrote:

Looks like a Mikuni VM series. Measure the inside diam of the (engine side) bore. Great project, looks like a fun one.

The I.D. on the engine side is 29mm, the slide itself is 30mm and the throat is 40mm. Now, how do I use that info to figure out what model it is?

Here is a link to Mikuni's manual, the deminsion chart is all the way down at page 14: www.mikuni.com/pdf/vmmanual.pdf

Yours looks like an older model. Yamaha used them on the R5's and RD's until 75', and changed them slightly in 76' for the RD400's (like in the manual link)

A VM 28 (I am measuring up a RD350 VM 28 as I write this) measures i.d. 29mm engine side, i.d. 40mm on the air filter side, and the slide is 30mm......ding ding ding! I think we have a winner! You my friend have an older Mikuni VM28, left side. Rebuild kits are still avaiable by Keyster, K&L, and Mikuni. Hope this helps ya out.

Oh yeah, a Benelli Mohave fuel tank would look sweet on that thing, check this out... cgi.ebay.com/ebaymotors/Cafe-Racer-Gas-T...fPartsQ5fAccessories

Thanks RLB!
And the Mojave tank is one of many I have my eyes on.

Here are more pics. Notice how the bell mouth has extra "ports" or orifices whatever they're called compared to any VM29 I've seen.
I've heard of oil injectors on 2 stroke carbs...is that what they look like? But I've seen pics of VM28's for a Yamaha RD and they had two less openings.

scott s wrote:

Here are more pics. Notice how the bell mouth has extra "ports" or orifices whatever they're called compared to any VM29 I've seen.
I've heard of oil injectors on 2 stroke carbs...is that what they look like? But I've seen pics of VM28's for a Yamaha RD and they had two less openings.

....

Similar to middle pic below (intake entry portals).

But the middle pic doesn't have L nipple for vent hose (am guessing vent hose), as does the carb at hand. Nipple also on different side.

Good Fortune!

[Click on image to enlarge view.]