CruzinImage BS38 carburetor floats -- Review

TwoManyXS1Bs

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This is a follow-up to xjwmx's review thread:

http://www.xs650.com/threads/bs34-diaphragm-and-piston-from-cruzinimage-review.50651/

CruzinImage offers BS38 float pairs for 1970-1979 carbs.
Even though there's different listings for various year groups, they're all the same float set, 20-1J7FT-2.
CruzinImage-BS38-Floats.jpg


https://www.ebay.com/itm/70-72-YAMA...T-2-/142442236778?vxp=mtr&hash=item212a380b6a

His store:
http://stores.ebay.com/cruzinimage-...42600011&_sid=526414511&_trksid=p4634.c0.m322
 
They come as a pair of floats with new hinge pins.
CruzinImage-BS38-Floats01.jpg


First examination is the pivot hinge.
The new floats match my OEM float pivot hinge opening. My OEM pins are brass, the new pins are stainless, and match in diameter and length.
CruzinImage-BS38-Floats02.jpg
 
Comparison pic of OEM to new floats.
CruzinImage-BS38-Floats03.jpg


Something seems a little different.
CruzinImage-BS38-Floats04.jpg


The new floats have slightly thinner float bodies.
CruzinImage-BS38-Floats05.jpg


The new float bodies are about 10% thinner, and will have about 90% of the buoyancy of the OEM floats. This could affect the proper float height setting. I plan to use the "clear tube method" for setting these.
 
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good write up 2M and a good price and quality item too . I guess with something like floats even the OEM floats would have required some fettling at the factory. Whether they actually got them or not is a moot point ;)
 
I kind of remember the rocket equation, but not the boat equation. Not sure if smaller means less buoyant.... Less force against the seat maybe. I think jetsRUS is selling both aftermarket and genuine at different prices.
 
... Not sure if smaller means less buoyant.... Less force against the seat maybe...

In this case, the reduction in surface area (which represents the amount of sheet brass used) is not as great as the reduction in volume, so the float density is higher, and will set a little lower in the fuel.

My brain went offline today, took a day off, so haven't progressed on this.

Took a piece of 0.100" (2.5mm) rod, fitted into the float hinge, took pics.
CruzinImage-BS38-Floats12.jpg


Staring at the pic, it seems that the float bracket was soldered on crooked.
CruzinImage-BS38-Floats13.jpg


It's off by almost 3°.

Rather than bending and twisting the floats, what I really want to do is make some sort of fixture that'll hold the floats, and/or the bracket, and do a rapid resolder of the bracket's joints. So, I'm in contemplation mode...
 
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Sometimes I think that we too readily rely on manuals and handbooks without bothering to fully understand how things were designed to work.
This attitude gets the job done most times but if we were to take 2Ms approach and really get to know our bikes components more intimately then we would not only be better able to better diagnose and correct problems due to our comprehensive understanding of how a thing is intended to work but also to make modifications and adjustments to optimise reliable operation and maximum performance and efficiency.

From memory I believe the recommended maximum tolerance for float height at setting is +- 2.5 mm which is quite a considerable latitude so clearly Yamaha didn't think that the float height setting was a particularly critical factor in reliable operation of the fuel supply and regulation within the float bowls however over 30+ years of DIY butchery and wear takes its toll on precision.

That said ,..the closer we get to zero tolerance within the float pivot system the more reliable performance one might expect but at some point there would be insufficient tolerance in the pivot pin/ post/ float assembly which would likely have a greater detrimental effect than a too loose float pivot pin/float fit due to friction.

Float height is of course just one very small part of reliable fuel regulation and it needs to be seen in context with all the other important parts of fuel regulation particularly the angle of the float tang to the float needle valve and general friction within the float needle assembly.
Something that is set, adjusted and tested on the workbench may very well perform quite differently when working at an angle or under acceleration deacceleration or even with the bike leaning on the side stand.

I look forward to following 2Ms exploration into the operation of the Mikuni cv carburettor :)
 
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Rather than bending and twisting the floats, what I really want to do is make some sort of fixture that'll hold the floats, and/or the bracket, and do a rapid resolder of the bracket's joints. So, I'm in contemplation mode...
Here's what I would try first. Unsolder the bracket from both floats quickly as possible, using a butane micro torch. Stick the floats to the table using Blu-tack. Quickly solder the bracket back on with the micro torch.
 
Yeah, the best way would be to unsolder the thing, and remake it.

I've figured a rebending operation at a certain point near the hinge would also work, but that grinds my gears.

Spent most of today researching various numerous offerings of these floats, and found a disturbing intermix of straight/warped and narrow/wide floats. Whatever these new floats were originally built for, they've become infused in the supplier stream, some even being sold for the outrageous OEM price.

Think I'm going thru burnout.

The floats offered on MikesXS show a huge fitment table covering bikes from 1963 to 2005! Click on the "fitment" tab and hang on:

https://www.mikesxs.net/yamaha-xs65...79-bs38-cv-oem-256-14985-00-127-14186-00.html

Their float pic shows the proper, wider float cells, but is that what's sent out?

Starting to think that somebody figured out a suitable interchange for these floats, and separating the properly dimensioned and built floats from the knock-offs is now near impossible.

Continuing the grinding...
 
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One time I had to get into my carbs and I adjusted the floats about 1/2 mm in the rich direction. I was sure there was a big difference; you could even hear it in the exhaust, more throaty instead of lean sounding. But consider how the floats bounce around in there while riding. Probably, and this might have to do why there arose some questions on bs-34 height setting, is the only thing that matters is that they are able to shut off the fuel under some set of circumstances. It's kind of an interesting physical science and statistics problem I think. You might think the open and closed state are in some kind of equilibrium, but I think if you shook the carb it would eventually overflow. Or rather it would depend on the rate of flow through it but that is arbitrary.
 
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It's an age since I last did any buoyancy figuring.
Otoh, gut instinct tells me the original and the replacement are so far up the buoyancy tree that they'll shut off just as well as each other (unless the replacement is bent and twisted, of course). In other words, they're not cruising on the edge of buoyancy, like a liferaft full of drunken leprechauns.
 
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