Topic: Brass vs Black "Rubber" Carb Floats

[34barab]

After ultrasonic cleaning the brass floats from a 71 CB750K1 carb set, inside one of the floats there was a little bit of fluid.  I think there's a couple of tiny leaks around the circumference.  The solder plugs are still in place.  How can this be repaired?

Also, I have a spare black rubber float from a later set - can you use this one in one carb while the other three use brass?  Do they have the same density?  Will the floats heights be different for brass vs rubber?

[ekpent]

  If it was me and I have done it, I would replace all 4 of the brass ones with the later black style from a 1972-76 K model bike or 75-76 F model and be done with it and not have to worry about getting another 'leaker'. These things are getting up in age now and Honda probably got rid of them for a reason in 1972. Old Suzuki brass floats are prone to leaking with age also.
  I am sure people have fixed them, I've done a couple of Suzuki. I used to set them close to my woodburner and when they heat up a little you will see where the leak is as the pressure builds inside and it get a wet/damp weep around the hole if fluid is inside. Sure other light heat source would work also.

[34barab]

That's a tempting thought.  If I go with all rubber, does the float height change?  Presently using 110 and 40 jets.

[BenelliSEI]

I’ve repaired a few. If you dip them in very hot water you will see air bubbling out at the crack. I then drill a tiny hole in the centre of the split and shake the float until it is empty. A few minutes with a hair drier, hole facing up, and it will be dry. Sand the spot, flux, and a drop of solder.

Two problems...... the float gets heavier, so some compensation required when setting height. And, one that has started cracking, usually does it again. Go with the new ones!

Over the years, I’ve noticed most damage occurs when towing a bike (or race car) in a trailer. Especially over long distances. The shaking helps the float chamber dry out quickly and the floats “rattle” for the whole trip. In side draft Weber carbs, the float cylinder occasionally fell off the arm! The solution is to open the tap (or switch on the electric fuel pump) every stop!

[Kevin D]

I have 2 of each type of float in my CB, and I am replacing the original brass one at a time. The bike runs like a top, 48-50 mpg, and doesn't seem to mind a bit.

I did a little arithmetic and figured that there has been about 1800 gallons of gas through my tank or 450 gallons through each carb. 2 floats, and one float needle valve are all I have ever put in these carbs. Oh, rebuilt petcock, new 5.5mm fuel lines too... but that's not the carbs.

[ekpent]

That's a tempting thought.  If I go with all rubber, does the float height change?  Presently using 110 and 40 jets.

Float heights stay the same on both as you adjust them to your needles.

[34barab]

Just to be clear, if the original brass float heights were to be set at 26mm (per manual), then having brass and rubber floats  in one set of carbs would all be set at 26mm? 

[evinrude7]

i've found that 26mm on the 657 or 7a carbs is a little low with the rubber floats.  only by a couple mm's but still low.  however i never had brass floats to compare.  the little tang that depresses the float needle can be off some too.  clear tube got it spot on.   

[Alan F.]

I've read somewhere that the 10% ethanol fuel affects float height, IIRC to compensate float height was set 1 or 2 mm higher, has anyone heard of this?

[pjlogue]

I would doubt a 10% EtOH mix would effect the density enough to warrant changing float height.  EtOH weighs 6.6 Lb/gal.  Gas is !6.2 Lb/gal.  The density of a 10% EtOH gas mix is 6.56 Lb/gal.    That's 0.4% density difference.  For most riding, adjusting the idle air would be enough to compensate.  I think going up a number for the slow jet would be too much. 

-P.

[Doobie]

FYI, you can still buy the brass floats on eBay if you go that route.
https://www.ebay.com/itm/Honda-CB100-CB125-CB350-CB750-Brass-Carburetor-Float-Pin-16013-286-014/162686924343?hash=item25e0e57637:g:CpwAAOSwN5hcF2xt:sc:USPSFirstClass!02632!US!-1

[ekpent]

FYI, you can still buy the brass floats on eBay if you go that route.
https://www.ebay.com/itm/Honda-CB100-CB125-CB350-CB750-Brass-Carburetor-Float-Pin-16013-286-014/162686924343?hash=item25e0e57637:g:CpwAAOSwN5hcF2xt:sc:USPSFirstClass!02632!US!-1

Interesting reading the add that the same float was used in so many different carbs/machines and they go back a ways in years. Great option for a restorer who wants the bike all perfect inside and out.