Need help ID'ing these Mikunis...

[Garage Specialty]

Couldn't find any specs online that match up to these:

44mm ID x 55mm OD - filter side (A)
32.5mm ID x 43mm OD - (approximate) engine side (D)
End to end = 113mm (B)

casting numbers 153 13 on both carbs (engine side)
and one has b 63 and the other has b64 (left and right pair)

97.5 main jet
2.5 slide
30 pilot
2.5 air jet
88? p-4 needle jet (may be 38 and not 88)

***to note there is no large drain in the bowl like i've seen all the other Mikuni VM's.

Thanks!

 

[grizld1]

Welcome, GS!

I doubt that this is anything you don't already know, but back in the day Mikuni produced quite a few special application carbs for which specs are no longer easily available. Your spigot OD and intake bell OD, for example, don't correspond to dimensions of "standard" VM aftermarket carburetors in the range of your venturi diameter (nominal 32 mm.), and all VM aftermarket carbs in your venturi range had the usual fat plug in the float bowl. Mikuni also doesn't show a series 38 or 88 NJ in their aftermarket VM parts lists; the closest shown is series 188, listed for Kawasaki flange carburetors. The AJ has me scratching my head; Mikuni offers nothing larger than #2.

I have some carbs that show similar weirdness. The basic design is TM33/8010 4-stroke pumper. One pair shows strange accelerator pump nozzles with oblong bases; nobody seems to know what they fit, and the AP nozzles are currently unavailable. I have another bank of 4 in the same design with fixed air jets, both MAJ and PAJ. It looks like you have another orphan carb set.

The good news is that the 2.5 slides and P-4 NJ should be in range for tuning your 32 mm. carbs for the XS650, and VM32's take series 6 needles. If I were trying to dial those carbies in, I'd start with 6F9 needles, a range of PJ's between 20 and 25, and mains between 175 and 185 (might have to go to 190 to compensate for the slightly lean NJ, but smaller venturi size should compensate for that anyway). Spigot OD won't be an issue. It's the same as the spigot OD of the VM36, and boots for the OE BS34 work well with those.

Good luck!

 

[Garage Specialty]

Thanks that was a great reply. I'm on the fence about using these but may just bite the bullet on the jets.

Thanks again!

 

[Paul Sutton]

Externally they do look very much like VM32, but not from the motorcycle market e.g. those large fuel drains on the bowls. Could these carburetors have originally come from a snow mobile (Polaris) or ATV??

 

[grizld1]

You're welcome, GS. Those carbs look like they're worth some expense of time and money. I like the cable pull choke actuators; you'd have to spend some serious bucks to install those on aftermarket VMs. You can run cables to a junction tube, then to a bar mounted choke lever from a 1960's Suzuki or Brit bike; makes control during warmup much easier than reaching down and twiddling a pair of levers. 32 mm. of unobstructed venturi is plenty for an XS650 street motor; it's roughly equivalent to a 34 mm. obstructed by a throttle plate and should give superior throttle response and low to mid rpm tractability. A dyno comparison to a VM34 would show loss of a fraction of a horsepower at wide open throttle, but you'd never feel that difference on the road.

 

[c3camdaymday]

Couldn't find any specs online that match up to these:

44mm ID x 55mm OD - filter side (A)
32.5mm ID x 43mm OD - (approximate) engine side (D)
End to end = 113mm (B)

casting numbers 153 13 on both carbs (engine side)
and one has b 63 and the other has b64 (left and right pair)

97.5 main jet
2.5 slide
30 pilot
2.5 air jet
88? p-4 needle jet (may be 38 and not 88)

***to note there is no large drain in the bowl like i've seen all the other Mikuni VM's.

Thanks!

Those are gt500 Suzuki carbs from around 1975 trying to fit a pair to xs650 C at the moment

 

[Paul Sutton]

GT500 - What a grunty machine. Very easy to wheel spin but the turning circle was a bit too big. A friend had one and he would pull up outside then start spinning the back wheel. There is one for sale on Eb@y UK at present - US Import.

 

[grizld1]

Hey GS, how did those carbs work out for you?