Last week with the promise of an impending heatwave I thought it best to finally get around to sorting my Z13 carbs, cognisant of all the helpful comments.
Could see absolutely nothing untowards to cause No.1 float valve to malfunction, thorough clean, double cherck and and reassemble and she is back on song - none the wiser as to what was causing fuel to overflow via the airbox breather.

Repeated start ups and 5 short journeys and she is again behaving herself: Today went for a bimble to hrough some of the local villages, ran absolutely perfectly: couple of pics of her sunning herself in the freak 27C temperatures.





Just hope she continues to "play nicely" throughout the summer
Cheers Tim

Hi all, my old '79 has a worn latch on the gas cap so if I fill her right up I get some fuel leaking out around the cap, I am going to look at it one day, the reason I mention this here is that i'm pretty sure the vent line is blocked, I've tried compressed air both ways and even tried to stick a wire down the tube but nothing seems to get it's way thru, any ideas on how to clear the line ?, I don't want to force anything down there as i'm afraid that I may puncture the line and don't want to stuff up the tank having fuel piss out the overflow from a hole in the line somewhere inside the tank, at present with the slightly loose cap it runs ok but would like to have the cap seal better, thanks for any suggestions, cheers Pete.

The "System" that's being discussed does both. It's a vent so the tank can remain at atmosphere as the fuel level changes and it's also a drain for a fuel overflow condition. The hole in the breather helps avoid a vapor lock in the entire length of the vent system, allowing vapor and liquid to be discharged freely. Think of that little hole working in the same way as a plumbing vent pipe that for a good reason must be within a required distance from the sink-drain.

Kawboy wrote:

stocktoy wrote: Looking at the images of the aftermarket and the OEM fuel caps I would think that you'd get fuel splash because there's nothing there to draw the fuel down the overflow tube correct me if I'm mistaken

You're losing me here Stocktoy. That hole in the top of the tank is not part of an overflow system. And when all of thr right parts as designed by kawasaki are in place, fuel nor air can go "down" that hole and out to the ground because the fuel tank breather is a one way valve only allowing air into the tank.

The fuel tank breather is the item below item #2

My thinking was that if the OEM cap had a nipple on it that went into the vent tube thereby letting any expanded fuel vapor/raw gas flow to the ground that if the nipple isn't there and the cap is vented as you feel the non OEM one is then it vents under the cap cover (under the cap cover - my thoughts) and would allow the vapor/raw fuel to expel on to the top of the tank (on my 79's I don't have that check valve in the hose - just the rubber hose)

I believe the breather could cause all sorts of trouble. I'm sure the fuel in the tank when heated up under the sunlight will vapor off somewhat and if it can't relieve to atmosphere, could build up pressure and possibly overcome the floats in the carbs and push fuel (overflow) the carbs. This is a complete guess at this point. The breather may be an over pressure relief device as well? I find it hard to believe that Kawasaki didn't think of pressure buildup in the tank under sunlight or heat from the engine.

stocktoy wrote: Looking at the images of the aftermarket and the OEM fuel caps I would think that you'd get fuel splash because there's nothing there to draw the fuel down the overflow tube correct me if I'm mistaken

You're losing me here Stocktoy. That hole in the top of the tank is not part of an overflow system. And when all of thr right parts as designed by kawasaki are in place, fuel nor air can go "down" that hole and out to the ground because the fuel tank breather is a one way valve only allowing air into the tank.

The fuel tank breather is the item below item #2

Looking at the images of the aftermarket and the OEM fuel caps I would think that you'd get fuel splash because there's nothing there to draw the fuel down the overflow tube correct me if I'm mistaken

If you can't get it fixed , the cheap replacements do fit and work , but as Scotch mentioned , they have no breather. Maybe the tank overflow pipe allows air into the tank as the fuel is used ? I had a look at the replacements on the german site , and from the small photo they have , they look like the ones I bought - the rather pathetic keys they show sitting in the lock is the give away. Maybe someone who has bought one from them can verify- there are not many options .

If I'm not mistaken this happens to all our bikes especially when it is on the side stand, that's why number one gets filled up. only way to avoid this is to remember to turn your petcock to the off position. It's also been reported that if your still using the original petcock fuel can still make its way into the cylinder and some members have installed a second inline cut off valve to stop this.

These previous post may be of interest.
Fuel Overflow

Fuel

You may find the root cause by reading the FAQ section, when you navigate to the Faq section use your browsers search facility and search for 'fuel', you may find your answer there

My carbs failed the leak test which means,on this bike, that any overflow of fuel will end up in the inlet manifold or in the airbox- not good. To that end I have just finished fitting the three new float valves I got from Allens Performance. I will pit pictures here because although they are very high quality items, they are slightly different to manufacturers OE spec.



As you can see the valves are slightly shorter which means they will not close when the chamber fills with fuel. On the Z13 the floats must be set so that the valve will shut the fuel off with the float in the level position. To get this to happen Ihad to reshape the tab on the float that actuates the needle valve.



The valve bodies themselves are slightly different and have a second O-ring that goes under the horse shoe shaped valve holder. The valve bodies are a satisfyingly snug fit in the carb bodies.

Next I ran the tops and bowls through the polishing wheel and finished them off with a set of new stainless bolts bought off Ebay for next to nothing
The final things to do were to reassemble the choke parts and leak test them again. Thankfully they have stood there all day with petrol above them and not leaked a drop. Job done

www.kz1300.com/index.php/forum/carburato...over-flow-drain#6707

I've converted three sets of carbs to incorporate this overflow. My own carbs too. This is not intended to circumvent other concerns but this mod works as intended and the Hydro-locking risk is eliminated.

I and others over the years have made numerous comments and referrals to Fuel-valves, fuel line routing, fuel-solenoids and fuel filters. It's all there if you take some time to look for these recommendations.

A leaking stock fuel valve can be repaired if the internal damage is not too significant. The reason they leak is a result of the internal tank-filter being removed or damaged. The rust and any other debris gets into the valve and scores the plastic valve-cone and tapered bore of the body. The fuel will then leak using the scratches/gouges as a path. If the damage is minimal the plastic cone can be "lapped" into the body. I used some polishing compound as the "lapping' medium and used a cordless variable speed drill and a "slotted" driver to spin the cone within the body. For my own - It worked as planned and the valve was restored and shut off as intended. If the gouges are too significant then this will not work but you won't know until you've tried.

Regarding: .....<For anyone looking for the floatbowl overflow modification,you can send your floatbowls to this co. after contacting them.
sites.google.com/site/shoodabenengineering/ click on"pricing"....I think they charge $80.>


Note that this is for a "traditional" drain for a carb that has a Siamese float, allowing the drain to be inserted in the center of the bowl, extending upward. This will not work on the "1300" carbs.

It will be interesting to see if they "boot-leg" my idea though !

I used to get this issue with my B2 and I don't have the ballast resistor as I have a Dyna ignition system with three ohm coils. When I was younger I would have just taken the opportunity to have a cigarette but I don't smoke any more.

I only say "used to" because my bike is still off the road. As far as I can tell it will probably still suffer this issue when it returns to the road as I never got to the bottom of it.

I'm now wondering if the carb overflow modification documented by Scotch would help with carb boiling issues? I had wondered about pressure build up in the larger B2 fuel tank but I've checked the tank breather is clear - however - I can't vouch that the circuit to it through the fuel cap works effectively.

I guess Momma K found there were heat issues with the B2 tanks as they installed a thermal barrier on the underside of the B2 fuel tank. I don't think this was standard on the smaller A1/A2 tanks.

Hello , For anyone looking for the floatbowl overflow modification,you can send your floatbowls to this co. after contacting them.
sites.google.com/site/shoodabenengineering/ click on"pricing"....I think they charge $80.

A recent picture here and many threads here and elsewhere regarding bent rods from cyl. Fuel-lock gave rise to this idea. Here's some photos of a carb-bowl over-flow I just installed on my own '80 carbs. Bench testing was accomplished with an actual body & bowl. The final location of the over-flow tube was determined by testing various outlet locations and various carb-body angles, fuel levels and needle-valve flow rates. I was satisfied enough to proceed.
NOTE: Something became very apparent when testing my design. Neither my design nor a "factory" over-flow is capable of draining any bowl which is flooding due to maximum fuel flow through a wide open needle-valve. Clearly, by virtue of the factory design which has a restricted opening, the purpose of the over-flow is to deal with a defective Fuel-valve,needle/seat or O-ring which is "leaking". My full-open tube design should inherently out-flow more fuel in this case and is less prone to plugging as it has no tiny "metered" inlet as is the case with most of the factory designs I looked at.
There are some obvious differences between my design and typical overflow tubes. Whereas the standard location for an over-flow is the center of a float-bowl, the single float location and unique bowl design of the Mikuni BSW32's forced an alternative location.
1) My over-flow is on the left side of each carb. This is the "high" fluid side when the bike is on the side-stand.
2) The tube is installed in the base of the carb-body, not the bowl.
3) The 1/8"brass tube I've used is not "metered". It is full open diameter. I believe the intent of reducing (metering) a drain tube is to reduce fuel loss when the fuel sloshes around. My higher location in the body seems to deal with this while providing a faster rate of drain, if needed. That's my theory, anyway. The final discharge location is optional but common sense must prevail.
Several details need to be emphasized, given the way I proceeded:
1) You must use a brand new "sharp" drill. I chose not to "center-punch" a starting point for obvious reasons. The new drill dealt with this omission easily.
2) Block-up the carb-body solidly so one hand can hold it securely. I used a drill-press. Hand-drilling should work satisfactorily.
3) The point of the drill is not going to make 360 contact initially due to the angle of the body where it is being drilled. A sharp drill with very little contact pressure will "mill" the high-side until the drill point is making full contact. If you force the starting procedure the drill will skip-off. The location of the drilled hole is critical.
4) Using a 1/8" bit for 1/8" tubing gave me a loose fit. This was desirable so the tube would have an epoxy coating inside the hole. Additional epoxy was used inside the body for strength, and I believe is required. Note the left and center carb drain is angled forward. This was strictly for esthetics to minimize the "clutter" under the carbs.

As with anything involving gasoline, Implement at your discretion.

The '79 carbs have been removed and the '80's with the drain have been installed. Once the carbs were syn'd i went for a ride around the block. Riding, on the center-stand or the side stand - All appears OK. Any further pros or con will be posted.