TOPIC:

Issue with fuel dripping while resting on the side-stand, but none when the bike is on the center-stand.
The drip only happens after the engine is turned off, and the bike is left for a time to rest on the side stand. Then, after a small measure of fuel eventually leaks out, the dripping stops.

My latest attempt to correct this incessant and annoying little problem, was to reset the floats to 19 mm versus 17mm+/- 1 mm. per the Mikuni single-sentence instruction booklet, which caused the fuel level to drop a drip, but not sufficient to stop fuel from breaching the overflow tube (located way up-high inside the float chamber btw), and out from carb #1.

This RS34 set was purchased new by the PO in 2015, and was used for one riding season before being removed from service.
When it arrived here, I immediately pulled all the jets, floats, and float valves to examine and clean. I found some residue buildup in a few areas, but I didn't see any on the float valve needle tips or the orifice that they seal. One area of buildup was found between the float bowls and carb bodies where fuel injects the pump nozzle in each throat bore, at the location where the bowl gasket prevents fuel from leaking.
Could a clogged or faulty check-valve allow the accelerator pump fuel to drain back through its isolated system into carb #1, making that one bowl overfill?

Does Mikuni spec out the fuel level in the carbs so the clear tube method can be used to measure fuel level? You would have to make a tool but that shouldn't be difficult.

I'm thinking one of the gaskets on the needle seats might not be sealing correctly. A little smear of grease on them helps old ones to seal like old bowl gaskets.
Steve

Nessism wrote: Does Mikuni spec out the fuel level in the carbs so the clear tube method can be used to measure fuel level? You would have to make a tool but that shouldn't be difficult.

Got the clear tube tool from Z1 Enterprises last year. It works like a champ, but there is no clear tube level spec for RS series carbs that I know of. Levels shown w/floats set at 19 mm, not 17 mm per spec.:

Right side, on center-stand


Left side, on center-stand


Left side, on side-stand

swest wrote: I'm thinking one of the gaskets on the needle seats might not be sealing correctly. A little smear of grease on them helps old ones to seal like old bowl gaskets.
Steve

Hmm...
Great suggestion! I will check that out. There was dried fuel residue on the o-rings, and some caked on the carb bore surface where they seal.
I may go ahead and reset the floats to 17 mm. while I'm in there.

daveo,
your photos show that the fuel level is too high. The fuel should be a few mm below the top of the float bowl. I'd bend the float tangs some and get the level lower.

Nessism wrote: daveo,
your photos show that the fuel level is too high. The fuel should be a few mm below the top of the float bowl. I'd bend the float tangs some and get the level lower.

Perhaps this perceived discrepancy is why there is no spec for the clear tube method on Mikuni RS series carbs.
The levels shown in the photos have the floats already set 1 mm. out of spec at 19 mm. rather than 17 mm. +/- 1 mm. The floats would likely need to be set at 22 mm.+ for the fuel level to drop that much, at which point there may not be room in the bowls for them function correctly. Mikuni does not suggest such alternative settings for the floats.
Last year when I ran the clear tube test on my sold set of RS36's, the results were exactly the same, so I think the RS series carbs were uniquely designed to have fuel levels higher than other types of carbs.

IMO, the fuel levels are too high, and should be below top of float bowl.

Measured float height is correct ONLY when it produces the correct fuel level.

A true overflow tube located inside a float bowl would usually be expected to have it's top opening slightly above the designed service fuel level and below the top of the float bowl (i.e., below the float bowl gasket).

I don't know if it's possible to install the float upside down on these particular carbs.

Good Fortune!

Patton wrote: IMO, the fuel levels are too high, and should be below top of float bowl.

Measured float height is correct ONLY when it produces the correct fuel level.

A true overflow tube located inside a float bowl would usually be expected to have it's top opening slightly above the designed service fuel level and below the top of the float bowl (i.e., below the float bowl gasket).

I don't know if it's possible to install the float upside down on these particular carbs.

Good Fortune!

This suggests that faulty information has been printed in Mikuni's Owner's Manual and Tuning Guide, and that every owner of RS Series Carbs has been instructed by the manufacturer (including everyone else) to set up Mikuni RS Flatslide carbs incorrectly for years...

It doesn't surprise me though, since there are two such instances of faulty information printed in the Mikuni RS Series Carburetor Application Chart. The chart indicates the spigot diameter size on the RS34-21-K is 42 mm. when it actually measures 40 mm., and the recommendation to use RS36 size on the Kawasaki KZ1100, which I chose to follow instead of the wise council from forum member's here, who suggested that size was too-big.

Float height is an inexact method of controlling fuel level in the float bowl. If done correctly it should get you close but there are a lot of variables in play. For example, if the weight of the float is compressing the float needle spring then you need to hold up the float while measuring, and that typically leads to inaccurate height measurements. Also, if the float needle spring is weak the needle seat pressure level won't be up to the proper level and the fuel level will be higher. Most Kawasaki FSM's don't even list a float height spec for this reason.

Going back to the photos, you have at least one carb with a fuel level noticeably higher than the others. Is this the carb that is leaking? If so, I'd address this first.

Here, for reference, is an earlier thread seeking “clear tube” and “fuel level” information as to RS34 carbs (with excellent pics): www.kzrider.com/forum/3-carburetor/60229...-please?limitstart=0

The purpose of adjusting float height is to achieve the correct fuel level. Boo on Mikuni for inexplicably failing to provide a “service fuel level”. Which thereby makes it impossible to confirm whether or not the float height adjustment achieved its purpose.

One side question (probably stupid, I know) --- Is it positively certain that the tube shown below is an overflow tube and NOT a vent tube?



The reason for asking is that the Mikuni description includes the following:
• Float Bowl Vent: Allows atmospheric pressure into float bowl for fuel flow.
And I haven’t been able to find anything from Mukini that mentions an overflow tube or an overflow circuit in the RS series.

As gaskets sooner or later deteriorate, a service fuel level above the gasket is an open invitation to leakage past the gasket.
If Mikuni designed the RS Series this way -- again, Boo on Mikuni.
On the other hand, perhaps Mikuni deems frequent or routine gasket renewal to be acceptable with high performance racing carbs such as these.

BTW, does the top of the pictured tube exit into the carb bore? Hopefully not, especially if it's an overflow tube, as an overflow circuit should prevent raw gasoline from ever entering the carb bore in the first place.

Good Fortune!

The size of the opening suggests a vent tube. Overflows typically have a small hole.
Steve