Mikuni cone carbs

[Guest]

Picked up a set of "conehead" smoothbores for my GS ... anyone know the Origin Story of them?

Dale Walker (at Holeshot Performance) gave some helpful into when I contacted him; he said they were built by Vance & Hines Racing for their drag bikes. I contacted Vance and Hines ("I know there's some old guy/gal back in your shop who knows something about them!") but no info there.

The carbs look like they started life as garden-variety Mikuni VMs, but were machined to accept a jet block and smoothbore slides. I'm guessing (?) Vance and Hines wanted smoothbores, & that Mikuni didn't have a product back then, so V&H bought a bunch of VMs and converted them.

Anyone know more about them?

 

[GregT]

Smoothbores were only available in 29 and 33mm. I'd assume they wanted something a different size so adapted them.
VM's you could get up to 44mm.

 

[Guest]

Finally got around to cleaning these. Interestingly, all run Keihin hex-style main jets, not Mikuni jets!

 

[chris]

Finally got around to cleaning these. Interestingly, all run Keihin hex-style main jets, not Mikuni jets!

HI, the mikuni carb on my cr250 has hex main jets. Are you going to install them and see how they work?

 

[gs11ezrydr]

I remember back in the early eighty's we ran 4 big bore dirt bike carbs in Pro Stock,Never seen these till now, Just about all of the dirt bikes ran hex jets back then,Thanks.

 

[Guest]

I've got a $#!+load of Mikuni mains and a fair amount of Keihin mains. What was surprising wasn't the tool-style (hex/wrench vs. flathead screwdriver), but the fact that the "cone carbs" use Keihin jets in (what started life as) Mikuni carbs. I'm sure they had their reasons ...

Thread pitches on the Mikuni hexes are very close to the Keihins but not identical; I think one's a 0.75 pitch, the other a 0.8.

Anyhow, I started installing the carbs w/ cables and hope to finish up this week. I'll get some photos up when I have them.