CruzinImage BS38 carburetor floats -- Review

It would be interesting to see if there's 2mm difference in natural float level between oem floats.

That 2mm variance in the OEM float level would require a 1.5 gram variance in the float weight, at the float cells. That's a lotta brass/solder for those thin-walled cells. It would be much more if the weight variance were at the crossbar.

... real Mikuni parts are made to close tolerances, cheap repops are not, and defects are going to make a difference.

That's why the OEM float level variance is highly unlikely.

...You can't get something for nothing, but if you buy cheap enough you can easily get nothing for something.

Well, it was worth a try.
Now we know...
 
Thanx, Griz.

Spent the evening going thru some older threads with carb problems, and I'm suspecting that some of those may have these narrower floats, creating an overfill/overrich condition.

For reference, here's some "clear tube" pics from 5twins and Robinc.

BS38-5Twins-24mm.jpg


BS38-Robinc-24mm.jpg


And my '71 XS1B BS38 float level with floats set at 25mm.

BS38-2M-XS1B-Carbs-FuelLevel-25mm.jpg
 
Well, it was worth a try.
Now we know...
You haven't answered the question would they have worked? I really suspect so, If not, I suspect the ones you got when you returned them would :) I also suspect you would get more variance than you think with oem floats. How many years, and how many machines, and how many subcontractors, and how many design changes, and how many scab laborers, and how many workers thinking to hell with a *$*%($ float, and how much testing, and how many slipped through the cracks anyway are talking about? And you think they will all float to within 2mm?
 
You haven't answered the question would they have worked?

(Time to employ some ambiguity matching)

Of course they would've worked. Just carry a bunch of spare, higher heat range plugs for the possible overrich fuel fouling. And a screwdriver, for clanking on the carburetor for the possible occasional stuck float.

If you order a screwdriver online for this task.
Stanley-60-004_1.jpg

And receive this:
depositphotos_166677630-stock-photo-worn-out-old-bent-screwdriver.jpg

Sure, that'll work just fine as well.

If you order up a handlebar, and receive this:
bent-xt225-handlebars.jpg

No problem. It'll also work.

If the purpose of a motorcycle is to get you from point "A" to point "B", then this model may be of interest to you:
MildNegligibleGazelle-size_restricted.gif

... those who'll hear it know. Of course some won't hear it, and they'll just have to feel it.

I reckon so...
 
I consider the carburetor to be a precision instrument, trying to function in a harsh environment, and should be treated as such.

In the old dealership days, you could toss-in new factory parts just as mindlessly as putting gas in the tank, and things would work. Nowadays, with questionable aftermarket budget parts quality, and a history of rough transport and storage, it is prudent to measure/check all replacement parts...
 
I'll toss these pics in here.
Right are stock floats, many were just kicking around in a carb parts tub.
Left are 650 central floats. kept in dedicated new parts drawers, they came in individual bubble wrap pockets.
The 3 bowls all measured 68mm +

DSCF7725.JPG


You can probably read the float ODS in my hen scratching, all left plenty of room to the float bowls.
I've installed at least 5 sets of the MM floats with NO problems.
I measured the round float "thickness" Came up with about 15.7-8 on all ten i tested tried to measure just the brass and not the solder blob as part of the thickness.


Couple of 78-79 stock choke plungers that I thought would snap before they came out of the bodies and some aftermarket Keyster, maybe? plungers, the neck on those aftermarket is 0.1 smaller diameter. So will probably be a touch sloppy in the rubber boot. I didn't measure the piston part but none of them would slide all the way into the choke bodies the stock pistons were stuck in.
View attachment 116775


DSCF7726.JPG

Guess I'm showing the manufacturing quality and consistency of the MM floats Every float had (about a mm) of twist, the left float is slightly above the bench top. I did not check the tool bar for parallelism.

DSCF7727.JPG

Full disclosure; these floats have been in MY inventory for ahem several years.
 
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2M, if somebody comes along with an even finer measuring stick and shows your work isn't really symmetrical your defense will be but it worked, same as Crusin's. One thing we learned is do a clear tube test with a new float. It probably wouldn't be wise to assume even a genuine Mikuni made last year would exactly replace one made in 1972...
 
I consider the carburetor to be a precision instrument, trying to function in a harsh environment, and should be treated as such.

Truer words were never spoken. In my 60th birthday thread, those of you who read it might remember just how much grief my carbs gave me until I FINALLY got everything dialed in. Even though I did my homework before the initial rebuild and ensured that all the correct jets were in place. I had those carbs off the bike and on the bench half a dozen times , replacing worn parts and eliminating air leaks and messing with float levels.
I had SO many issues before nailing everything down, now it just amazes me that I just go out and thumb the button and it starts and runs perfectly! They really are precision instruments, and they don’t like to work if they’re not dialed in.
 
Well, after all that fiddle-fussin' with these floats, I've decided to not use them, and just put them back in their bags, into parts storage.

Why? I've uncovered even more reason to avoid the thinner floats, due to reduced flotation, reduced reserve buoyancy. So, not gonna fuss with them. OEM it is...
 
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Aww....that’s understandable but too bad. I was looking forward to a real test of these and also of your realignment job 2M.
 
On the positive side, they survived a very harsh environment.
 
I understand the reduced flotation bit, but what is reduced reserve buoyancy? And by O.E.M. do you mean directly from Yamaha only, or do you think just genuine Mikuni, like the ones from 650Central, would do the trick? The Yamaha offering is awfully expensive, all their 650 floats are. That's what got me looking at the Suzuki ones.
 
I understand the reduced flotation bit, but what is reduced reserve buoyancy?

Well, a bit tricky and difficult to explain. Tedious, but enlightening. Made some graphs to try to get the idea across.

...And by O.E.M. do you mean directly from Yamaha only, or do you think just genuine Mikuni, like the ones from 650Central, would do the trick? The Yamaha offering is awfully expensive, all their 650 floats are. That's what got me looking at the Suzuki ones.

Gads, those expensive Yamaha floats. No wonder we're looking at alternatives.

I'd like to have some of *all* the offerings, to evaluate, test, compare. But, the main thing now is to avoid the "thinner" floats. I can modify the fixture to work on the wider floats, in case of crooked assemblies. Could go broke from ordering some from everyone. Then wondering if they'll do a bait/switch sometime later...
 
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