'78 KZ650B Fuel System Leak Mystery - Kawasaki Motorcycle Forums
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post #1 of 16 (permalink) Old 06-20-2019, 05:05 AM Thread Starter
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'78 KZ650B Fuel System Leak Mystery

I have an interesting problem with my '78 KZ650B - I noticed recently that my #3 carb was leaking out of the overflow tube; every 45 seconds or a minute or so it would pee out of That #3 tube only - - OK, something in the needle valve, right?? I took the carbs out, opened them up, found a teeny little blade of grass in there, and thought my problem was solved - Nope. It kept doing it. (and Yes, I do have an inline filter in there).

A biker friend of mine said just replace the needle valve, there might be imperfections on it I can't see - OK, no problem. I replaced the whole needle valve jet with a new one, and #3 stopped peeing all over the floor...Awesome!...until #2 started doing the same thing!

#3 stopped, #2 started - I'm playing fuel Whack-A-Mole here and beginning to think the problem is not with the needle valve. Do I have a leaky petcock? And even if I did, wouldn't the needle valve, if working properly, shut off the flow of fuel until the fuel in the bowl dropped?

Another thing: I placed all four of the overflow tubes over a suitable catch basin, to stop the fuel from leaking all over the floor - but I found a smallish puddle of fuel UNDERNEATH the bike! And I have No idea where That came from! The carbs themselves are not noticeably leaking - just from the overflow tubes, from what I can see - -

The carbs are set to 23.5 +/- mm, fuel levels are set between the bowl and carb body as described in the wet-adjust/clear tube method....


What am I missing?
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post #2 of 16 (permalink) Old 06-21-2019, 07:54 AM Thread Starter
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Well, I found what I think I was missing: the floats were slightly off, so I think I was getting more fuel than necessary, but for the life of me I don't know why. When I redid the carbs the first time I had them set to 23.5mm+/- from the surface of the body...in any event I reset them, and am in the process of setting the gas levels via the wet-tube method. In case you're curious, or wondering where to get the little 'tool' for that, I got two of them here - Worth every penny, if you ask me...

https://www.ebay.com/itm/Mikuni-Carb...EAAMXQltxQ7icv


AND I found this post on KZRider which helped a lot to explain WHY my bike was pissing all over the floor - I hope it helps!
https://www.kzrider.com/forum/3-carb...ing-from-carbs
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post #3 of 16 (permalink) Old 06-21-2019, 11:53 AM
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Sometimes the overflow tube can be cracked where it meets the float bowl. Also, if a carburetor overflows, the excess fuel can end up in the airbox which has a drain hole at the bottom & there should be tubing connected to a nipple on the airbox.

Setting the floats to the 23.5mm spec doesn't necessarily result in the correct fuel level. I set mine precisely dry, then did the service fuel level check >> all 4 were off. So I redid the job by checking them wet via the clear tube method, setting them all to exactly 3.0mm below the bottom of the carburetor body. To speed up the process I made a simple carb stand w temp fuel supply using a large funnel & tubing, and I made a simple float support so that the floats or tangs wouldn't get mangled. Also, instead of bending the tangs, I flexed them X-number of times & only used 2 screws to install the float bowls for checking. I think it took a couple of hours to get the fuel level correct, plus the time spent getting set up. I wanted all 4 exactly the same at 3.0mm. probably not necessary, but that's what I did.

...

1981 KZ650-CSR. Competition, Sports & Road.
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post #4 of 16 (permalink) Old 06-22-2019, 09:04 AM
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If the carbs overflow with the petcock in the off position or it is the vacuum controlled type it is leaking also. If the vacuum type it can leak down the vacuum line and then the fuel might not come out of the overflow tube. They also have a small vent hole on the petcock body to allow the diaphragm to operate.
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post #5 of 16 (permalink) Old 06-24-2019, 10:38 AM Thread Starter
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Yes, its the vacuum type. I thought I had it yesterday - I measured my fuel levels in the bowls with the clear tube method, it was lining up about halfway on the upper rim of all the float bowls - about 2mm below the seam, so I thought it was good. Took the bike for a ride, filled it up, rode home, there was no peeing out of the overflow tubes; I loved it.

Got up this morning, and saw some fuel in the bowl I had placed under the tubes, just in case, and sure enough my #3 was leaking again! not a lot - but enough to make me think the jet needle wasn't sealing. I shook the bike a little, and some gas flowed out. Now, to be honest, I DID put the old jet needle back in because I thought it might've just been a case of bad float height; the old one didn't look bad; it wasn't dimpled or appear worn, which in turn led me to think it just might've been the float height...I corrected the float height again, put the old needle back in, went for the above ride, and today went out and found it leaking again. I'm an idiot, I know..,

So TODAY I go out, find the fuel in the bowl I put under the overflow tubes, and decided "Fcuk it - put the New one in;" I'm draining the carb bowls, and when I get to #3 and unscrew the drain plug, it just keeps draining...and draining...and draining...! (Found the problem, I think)… I stuff the drain screw back in to stop the flow, then go to take the tank off, and lo and behold the Petcock (vacuum operated, original 1978 Kawasaki petcock) won't stop draining either! That didn't happen before; but Talk about sticking a finger in the dyke...! And a full gas tank is Heavy!


I didn't find any fuel in the valves - it must've drained into the oil by now..(nice)…but anyway, I have the tank off; and its slowly leaking into one of my oil change bowls as we speak, so at least THAT's stopped for now - kind of...

I'm going to go over the carbs again, make sure my fuel levels are correct, and I want to ask if it's worth it to try to refurbish the old petcock, or...? I've read these original petcocks are crap, and I'm starting to believe it. If you have a 1978 KZ650, (A) did you have this problem too, and (B) what did you do to fix it? I can't think of anything else I can do to the carb - it is Spot On as far as measurements go; and I've also read that the petcock repair kits don't really work either! SO what are my options here...? Does anybody have a decent manual (or vacuum) petcock that works? I was also reading that Pingel petcocks are supposed to be totally frickin' Awesome - and they should be for $115 they want for one (!).


...Anybody..?
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post #6 of 16 (permalink) Old 06-24-2019, 11:21 AM Thread Starter
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Okay, well, Update: I went back out, took off all the bowls and filled each one with alcohol and attached one of the overflow tubes to it and blew thru it - care to guess which one I got bubbles out of?

Number Three! You Would Be Correct, Sir! Tiiiny little bubbles coming up from where the overflow tube goes into the bowl....Okay, so there's ONE symptom demystified...what do you think, a little JB Weld...? I know; if it breaks after it seals it I'll have another problem...or does anybody have another carb bowl they wouldn't mind donating?

I still have to figure out what to do with the petcock, though.



"I like my bikes like I like my women - Over 30 with lots of problems.."
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post #7 of 16 (permalink) Old 07-13-2019, 09:55 AM Thread Starter
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Update: what I did was take a soldering iron and attempted to solder the area around the base of the overflow tube. I wasn't sure if I got it - brass does not seem to like holding onto solder - but it appears to have worked. The carb is no longer peeing out of the overflow tube.

I also took apart the petcock and rearranged the 5-hole gasket in there - no more drips! I was also going to try making a shim for a fix I found online, but that didn't leave enough room to get the petcock faceplate back on, so I essentially just made sure it was clean and put it back in, and it worked.
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post #8 of 16 (permalink) Old 07-14-2019, 09:58 AM
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IF the carbs are overflowing a tad, I would consider the overflow tubes in the bowls are a likely culprit. Get a can of carb cleaner after removing the bowls and spray into the overflow nipple with your finger over the opening in the bowl. If you see carb cleaner go out sideways the pickup tube is cracked and would account for the minor leaking. Soldering around the overflow nipple is a waste of time. You can try soldering the tube that is cracked and that might make more sense. This has already been suggested so I am just restating.

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post #9 of 16 (permalink) Old 07-15-2019, 08:19 AM
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Don't waste too much time with the carbs, its the tap. Get in line basic 90 degree On/Off fuel tap from ebay and fit it in the fuel line below the tap. The tap issue is across loads of models of various manf. I have ZRX1100 in at the moment and its pissing fuel even after a repair kit. These taps are sh*t. When you park up for any duration, turn off the second tap.
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post #10 of 16 (permalink) Old 07-15-2019, 08:53 AM
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Some guys prefer a manual fuel valve. I prefer a vacuum petcock. I've replaced the diaphragm, but that's just normal maintenance. Results seem to vary on diaphragm replacement, but I installed a K&L rebuild kit with no problems (K&L stuff is made in Japan). Before installing the kit, I made certain the petcock body was in good condition w no scratches or pitting, and I buffed the mating surfaces w brass wool. The oem diaphragm assy for my KZ650 is still available at the Kawasaki dealer & it's pretty inexpensive, less than $20.

When setting the service fuel level, the reference point is the bottom edge of the carburetor body.
The Kawasaki service manual should have a drawing or pic.
....

1981 KZ650-CSR. Competition, Sports & Road.
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