What carbs for a buffalo

tz375 · Post by **tz375** » Fri Nov 14, 2008 3:39 pm

I almost gave this post a title of "best" carbs, but that left too much room for interpretation.

The question is simple - has anyone changed from early VM32 to BS40 or vice versa and if so was there any discernable difference?

I have pictures of Blueboy with what appear to be both, but I have no idea of their dates, so i don't know which came first.

I'm sure that larger flatslides would be an improvement, but that requires tilting the intakes for clearance, and I have enough other changes to do without adding that to the list if it can be avoided.

I should have said - this motor is for the street and needs to make more Hp than stock but at relatively low rpms.

cabz · Post by **cabz** » Fri Nov 14, 2008 3:49 pm

I have had both setups on my 73's the vms are ok but I think the bs carbs are generaly in better shape and once set are realy trouble free. since they have far fewer cables to play with it tends to be easier to adjust them.

as far as performance I think they are about the same

rngdng · Post by **rngdng** » Sat Nov 15, 2008 3:21 am

Blueboy has 34 VMs on it. The BS40s are good carbs, but they do hesitate a bit compared to the VMs. Ed has a 72 (which happens to have a 75 engine) with the VMs and it does power wheelies! The CVs (in my experience) won't do that. They are great for touring, but if you want performance, go with the VMs.

Lane

chainsaw · Post by **chainsaw** » Sat Nov 15, 2008 5:40 am

can somebody post a pic of the VMs? I am lost. where would one get some and how expensive are they?

tz375 · Post by **tz375** » Sat Nov 15, 2008 10:11 am

Thanks guys.

I suspected that would be the case, but figured that asking is a lot more reliable than guessing.

Lane,
With the 34's did you have to tilt the intakes or did you use longer intake rubbers to push them back behind the clutch hump?

GT Tim · Post by **GT Tim** » Sat Nov 15, 2008 10:31 am

I think I am about to learn something here.....

What is the difference between the VM and BS carbs? Assuming CV are the constant velocity carbs which I associate (maybe mistakenly since I have never owned a late model Buff) with '74-'77 models.

So if this is the case, (which may not be) what carbs are on the '72-'73s.

What years got what carbs?
I am slightly confused now...

GT Tim · Post by **GT Tim** » Sat Nov 15, 2008 2:16 pm

....did I just answer my own question???

http://cgi.ebay.com/ebaymotors/1972-THR ... ccessories

Wayne Meuir · Post by **Wayne Meuir** » Sat Nov 15, 2008 4:17 pm

The BS carbs are CV carbs, VM's are the standard round slide carbs that use a cable to move the slide. The are what is found on most bikes that do not use CV's.

Wayne

rngdng · Post by **rngdng** » Sat Nov 15, 2008 4:44 pm

Yep, what Wayne said. The CV carb Mikuni model number is BS40. And they are 40mm carbs, but they don't flow as well as the 34 VMs (round slide).

They cleared the hump using the mounts from the CV carbs, HOWEVER, some slight mods had to be done. The throats on the 34s are a lot smaller than the CVs, so you can either use mounts from a 73 model, which still have to be clamped really violently to get them to seal.

OR you get creative, and use the late-model sleeves, like so:

That's plain old PVC pipe, 1.5ID, I think, but anyway, it slid right onto the carb. I JBWelded the PVC adapters on , and used a 1/4" dremel bit to cut the groove in it. Now it fits the original sleeves perfectly.

Also notice on the first pic that I copied the vacuum port from the CV carb, and epoxied it in place. I made the hol in the carb the same size as the original vacuum port . It works great, and they've been this way for about 3 years.

Lane

GT Tim · Post by **GT Tim** » Sat Nov 15, 2008 4:50 pm

..So what I originally thought was right? There are TWO kinds of carbs. Round slides and Constant Velocity. not 3 kinds, right?

Wayne Meuir · Post by **Wayne Meuir** » Sat Nov 15, 2008 5:03 pm

YUP!

Wayne

Arne · Post by **Arne** » Sat Nov 15, 2008 7:13 pm

I have a set of 36mm flatslides for my project (mikuni TM), and had Eric mill the intakes flush and then angle them so the bowls miss the cases.

(the TM's don't come stock on the GT series)

I'll tell you how they run when I get those cylinders back!

Arne · Post by **Arne** » Sat Nov 15, 2008 7:20 pm

rngdng wrote:
Also notice on the first pic that I copied the vacuum port from the CV carb, and epoxied it in place. I made the hol in the carb the same size as the original vacuum port . It works great, and they've been this way for about 3 years.

Lane

Do you ever have any fuel delivery problems? I've heard the vaccuum diaphragms don't pump as much as open petcocks, but was going to run them on mine anyway...

Arne

GT Tim · Post by **GT Tim** » Sat Nov 15, 2008 7:35 pm

Arne wrote:I have a set of 36mm flatslides for my project (mikuni TM), and had Eric mill the intakes flush and then angle them so the bowls miss the cases.

(the TM's don't come stock on the GT series)

I'll tell you how they run when I get those cylinders back!

Any ideas on how these would work on a '72 T500 with pod filters and chambers?

Should I stick to the stock 32's?

Arne · Post by **Arne** » Sat Nov 15, 2008 8:47 pm

GT Tim wrote:
Any ideas on how these would work on a '72 T500 with pod filters and chambers?

Should I stick to the stock 32's?

I wouldn't hesitate to go to 34's, you'll want to think about 36's tho.

I'm taking a bit of a gamble on mine going to 36's, as with bigger carbs you lose throttle response and it makes it less 'streetable'.

The drag racers put big old carbs on but they don't necessarily care about throttle response.

This guy has some interesting things to say about carburetors and size.

http://homes.midmaine.com/~shoeman/inde ... dcarbs.htm

Note that he's writing about the reed caged RD motorcycle and not the piston ported T series, but some of it's applicable.

From what I've read about Lane's GT750 bike it runs good with 34's.

Note that flatslides are supposed to have throttle response like the next size down but wide open throttle flow like the next size up in comparison to round slide carbs, but I haven't run mine yet so I don't know that for sure (yet)

Good luck! Arne