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Yamaha Tech Originally the Yamaha XT600 Tech Forum, due to demand it now includes all Yamaha's technical / mechanical / repair / preparation questions.
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  #1  
Old 15 Jun 2009
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Gasoline Leak
Hi!
I've got a weird problem on my XTZ660 3YF, 94 mod.
When i have been driving for a while, it starts to leak from the overflow hose from the floatchamber. If I stop the engine, it stops leaking. I have changed the float valve needle, and the float valve seat. I have also set the float height.
What i think is weird about this, is that the leaking stops when the engine stops... And that it the leaking doesn't occur before i have been driving for a while, and when it starts leaking, it leaks a LOT!
Any suggestions??

Does anyone know what this hose does?(Marked ??????)
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  #2  
Old 15 Jun 2009
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If the bike has a vacuum fuel tap, that would account for the leak stopping when you stop the engine. You seem to have checked the obvious. Did you check that the floats actually float? A punctured or porous float would give exactly these symptoms. The float level check is done dry, and wouldn't tell you anything about the float condition.
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Old 15 Jun 2009
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Quote:
Originally Posted by lumzar View Post
Hi!

Does anyone know what this hose does?(Marked ??????)

I dont have a 660 but if it has vacuum fuel pump then that hose is what powers the pump.

is the leak definately coming out of the overflow and not dripping down it from somewhere else.

if its coming out of the overflow then i think you are right to suspect the float valve, there isn't an obstruction moving down and stopping the valve from closing?

oh and top marks for the diagram
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Old 16 Jun 2009
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i have suspektet that litle boks to be a vacum pump povered by the ?-hose, but when i blowed air in the tank hose, gasoline came out the hose that goes to the carb. and when i sucked the ?-hose nothing hapend, it seemd to be clogged, but when i blowed i the same hose, gasoline ran out of both the tank hose and the carb hose
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Old 16 Jun 2009
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if it is a vacuum tap it will have 3 positions 1 prime 2 on and 3 reserve
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  #6  
Old 16 Jun 2009
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its not a vacum tap, the possitions are on, off and res
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Old 16 Jun 2009
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i'd bypass the vacuum pump by blocking off the ? hose and fitting the fuel line from the tank tap direct to the carb.
if it still leaks under gravity feed then its definately a float/shutoff valve problem within the carb.
if it stops it leaking maybee the fuel pressure via the pump is too high and forcing the fuel through the fuel shutoff inside the carb either way its a carb fault.
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Old 16 Jun 2009
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Vacuume pump
The box marked ???? is a vacuum pump and is driven by the changing pressure from the hose marked ?????. The pressure changes as the engine turns over working the pump.

The pump requires sucking and blowing to pump the petrol from tank to the carb, vacuum fuel taps only require sucking to allow the petrol to run through.

I'd suspect your problem to be the float in the carb. Try setting it slightly lower than what you currently have and see if it is still leaking, or cleaning it out if you havent already done so as it could be some muck in the float valve seat.
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