Fuel leak when full

[VisionAirman]

My '82 Vision (3200 miles) leaks fuel from under the engine when full and shut off, but only with the tank full.  I have completely rebuilt the fuel petcock as it leaked when I bought the bike. Any thoughts as to what causes this?

Also, somewhat related, looking at adding a fuel gauge.  Hopefully there is information here for that modification.

Thank you in advance.

[fret not]

The 'best' method of adding a fuel gauge is to use a '83 tank that has the appropriate openings.  Other than that I think you would need to fabricate a float sensor like in a water tank.   There probably exists float sensors that would be suitable, but where to find them?  Industrial suppliers like McMaster/Carr, MSC, etc. might be a start.  Race shop suppliers might have something, and aerospace related companies would be a likely source.  An already in use design from the automotive industry might work.  Much depends on YOUR ability figure out what is needed, and how to fabricate.  Probably the easiest fuel indicator would be something that lets you know you have a few liters (5?) in your tank, which would give sufficient warning before running out of fuel. 

A tank with a transparent area that lets one see the fuel level would be handy.  This would require a plastic or fiberglass construction.  There was (long time ago, '60s) a small Japanese bike with a clear plastic tube on the outside of the tank, fitted to small elbow tubes near the bottom and top of the tank.  You could see the fuel level easily, but a tube like that is easily bumped or knocked free in an accident, and the resulting fuel spill would be a very bad thing.

[pinholenz]

A far less complicated "fuel guage" is to use your trip mileage meter to work out what your fuel consumption is on a demanding ride. Knowing that our tanks capacity is 17 litres, calculate the mileage you could achieve to run it dry. Allow say, a quarter tank, to get to your next gas station and you have a mileage that you can achieve without worry. When you fuel up, set the trip meter to zero.

At Fuelly.com, the average  MPG for an XZ550 under all riding conditions is between 36 and 39 MP/ UsG or 6.5 L/100km and 6.00 L/km

I usually start looking for a gas station after about 250km

[injuhneer]

Have you been able to see where the leak originates?

[jefferson]

If it's like any of the older vacuum petcocks they still leak even with new parts. I have been fighting this on my XS 750. New needle and seats didn't stop the fuel and filled the crankcase full of fuel. I suspect on yours fuel is leaking from the overflow tubes which means fuel is getting past the petcock and the needle and seat. At least the Vision has an overflow tube. Try some new needle and seats if you haven't done that and then you might try splicing an on/off in the fuel line.

[MikeScoot]

If it's like any of the older vacuum petcocks they still leak even with new parts. I have been fighting this on my XS 750. ...

Sorry to go a bit 'off-topic' but those XS750's were a gem - apart from their main bearing issues. The 120 degree crank timing gave a brilliant power delivery. I rebuilt my motor twice (main bearings both times) before crashing and bending the alternator end of the crank - so I hacked it off and put a bung in to keep the oil out of the sidecase. Went like an absolute rocket after that, but obviously the crank balance was way out. Rode it around a couple of thousand K's with a truck battery strapped to the back of the seat till the motor blew a third time and then I gave up on it, pulled the front-end off and put it on an XS2. But I have some extremely fond memories of that bike! I think one of the new Yam adventure bikes is also a triple. Probably nice too.

[jefferson]

I love the sound of a triple and was a major factor in getting this one. Our forum is gone, but from what I gathered when it was in operation was was the bearing issue resulted from the petcocks leaking and filling the crankcase with gas and diluting the oil which resulted in the bearings going bad. That's quite the bummer to have them go 3 times. That new triple Yamaha has is quite a nice one. I think I have figured a way to have an off on the stock petcock. Then I will just have to remember to turn it off and then on to ride.

[cvincer]

Non vac  on/off/reserve petcocks available on ebay for low cost (from China).  The one I got worked fine.  The outlet was to the right (as looked at when bolted to the tank) instead of the left...so the fuel line had to be a few inches longer.   I never had to run the bike on reserve, so can't comment on how far I could have traveled compared to the OEM vac petcock.

[VisionAirman]

Have you been able to see where the leak originates?

No I have not, haven't been riding as winter came and I have been on long hours (I am a govt employee).

Sorry for the long wait for a reply.  I may add a small on/off valve past the fuel petcock inline as a stop if the needle is leaking in the valve and overfilling the carb bowls.