'78 KZ650B - fuel dripping out of overflow tubes

wargoth wrote:

I have had good luck with this repair.

As far as the clear tube goes, I overstated what I actually meant to make a point. Most manuals do not have a dynamic float measurement. if you move the tube up and down at all during the test it makes it innaccurate because fuel cannot flow back out the float needle and you have increased the float bowl volume with the tube.
My Chiltons vintage manual (Motorcycle and atv repair manual 1945-1985, possibly the most useful shop manual for the vintage wrench-bender) states that the fuel level with the clear tube test is "2.5~4.5mm" using special gauge p/n:57001-208. This is a big range, while the spec for doing it the right way is 30mm or 1.2". Note that there is no + or - in this spec. Also be sure that the needle is fully seated, but the spring-loaded pin is not pushed in at all. I do this by holding the carb with the float pivot horizontal on top and the carb base flange vertical. I also use dial calipers locked to the proper measurement and use the depth rod on the far end from the dial.
Also note that the proper synch mismatch is 2cm, or approx 3/4"... not too much.
I will go get some pics and post them in a bit...

That's a good point about not moving the tube. When I did mine, I just stuffed the tube between the pair of carbs so I didn't have to handle it at all. Not moving that way. Thanks for being civil, it is all too common for someone to take offence at an opposing viewpoint. I feel that all the flamewars do nothing to help a man having trouble with his carbs. Put a gold star on your chart today.

sbruton, the reason that I asked about the ultrasonic cleaning was to see if there was a correlation between the ultrasonic cleaner, and cracked tubes. I used an ultracsonic on mine, and was wondering if all the high frequecy vibes didn't crack that tube. I guess that my theory is not definitive.

Good luck replacing the tubes. Sounds like a valid solution.

I am not sure why the tubes sometimes crack, stress risers from installation? Metal impurity? stress from vibrating? I actually suspect condensation fost heave from storing in sub-freezing temps. The water condenses in the metal from diffrential temp, and then freezes, then more water forms during temp change, and freezes again. ever expanding it cracks the brass so slightly. Had the one I'm posting pics of cracked around the base, but not bent I live in Spokane WA and it gets pretty cold here.

So as promised here are some pics

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best way I know of to adjust float height. I am not the electrical Wizard, but I do have a degree in M/C master repair and worked on all sorts of flying machines for 17 years and have an A&P lic.

also note that I am showing the caliper in the CENTER of the block foat. This is where the average fuel height is determined. If you measure this type of float at any other point, it will not be exactly right, even far off. Also dont forget to make sure the other side pod is the same height too, the frames often get misaligned from handling and stress. It is not hard to straighten, but be careful and use 2 pairs of pliers to do the work. Do not bend too close to the pod.
Round brass floats are easy, just measure at the highest point

if they dont all have the same bouyancy, they will never work properly. They are extremely precision made.
The float and needle have multiple functions, not only do they maintain the correct fuel height, but also meter the fuel flow volume. When the throttle is at WOT the fuel level actually is supposed to drop, metering the pressure balance in the main jet. Also, note on some carbs there is a float drop arm that only allows the float to drop so far, and sometimes you can even get a spec. for the correct float drop.
My '79 XS750 with an 81' 850 engine, would suck the float bowls dry with the stock 750 Mikuni's. Solution, bigger flow rate needle and seat. Problem solved

wargoth wrote:
"if they dont all have the same bouyancy, they will never work properly. "

Not so. Think of it this way, you have 2 beer cans, one is empty, one has 4 ounces of beer in it. You seal them both up real good so they cannot leak. You put them both in a bathtub with 4 inches of water in it. The empty one floats a little higher than the other, but they both float. Now, you add water to the bath tub until it is 10 inches deep. Both beer cans have risen 6 inches. It doesn't matter that one is more bouyant than the other, they still rise and fall at the same rate as the water. Ed

I mean, floats must weigh the same between the carbs. also the beer can with beer in it floats at its water line, not just a little lower. if they were connected it should approximately split the diff. in a balanced carb, too much.

If a brass float has just a little of gas in it, it is garbage. Unless you know a way to repair the leak in it, I have tried and had no luck.

testarossa wrote:

wargoth wrote:

I have had good luck with this repair.

sbruton, the reason that I asked about the ultrasonic cleaning was to see if there was a correlation between the ultrasonic cleaner, and cracked tubes. I used an ultracsonic on mine, and was wondering if all the high frequecy vibes didn't crack that tube. I guess that my theory is not definitive.

Good luck replacing the tubes. Sounds like a valid solution.

Hi Testarosa,

It seemed strange to me that the tubes were cracked, but my bike has been sitting for 15 years and I know some of those years were definitely outside. My theory is the same as Wargoth - must be water getting in there and freezing up.

Thanks again.

wargoth wrote:

I have had good luck with this repair.

Thanks for all the pics and information. This will help a lot. I found some 1/8" tubing and a small tube cutter at a local hobby shop. I hope to start the repair today.

I will let you know how I make out!