Post by wheezy on Feb 26, 2014 19:02:36 GMT -6
Hey guys. As you know I have had fuel issues in the last week, with stalling and hesitation and such. I changed the filter and hoses, and adjusted the carb and valves. I thought I had it licked, but it showed again when I tried riding to work.
I did notice something very odd when I started up at the gas station last week. The fuel gauge went nuts, registering all over the place. At the time I didn't think much, but then it all added up. I suspected the fuel pump, and found a new Mikuni on Amazon for 20 bucks. I put it on today, which gave me an opportunity to do a post-mortem on the old. For those that don't know, vacuum driven pumps have two valves, one is closed when the other is open, then they switch, which forces fuel from intake to outlet. I found the fuel intake valve had come unseated and misaligned, never getting fully closed.
This is where the gauge came in. I did notice a pulse, almost like a heartbeat, in the fuel gauge. Turns out as the pump would attempt to force fuel to the carb, the open valve allowed it to be pushed back into the tank, which made the fuel level fluctuate, which was indicated on the gauge itself. The diaphragm of the pump was in good shape.
Only after tearing it down did I realize I might have been able to fix it. Still, 20 dollars was not money wasted for peace of mind.
Here are pics of the broken pump, as well as when I reseated that valve. You can see the rubber seal in the first pic is not set right, and in the second the tabs of the valve poking out from the hold down bracket.
I did notice something very odd when I started up at the gas station last week. The fuel gauge went nuts, registering all over the place. At the time I didn't think much, but then it all added up. I suspected the fuel pump, and found a new Mikuni on Amazon for 20 bucks. I put it on today, which gave me an opportunity to do a post-mortem on the old. For those that don't know, vacuum driven pumps have two valves, one is closed when the other is open, then they switch, which forces fuel from intake to outlet. I found the fuel intake valve had come unseated and misaligned, never getting fully closed.
This is where the gauge came in. I did notice a pulse, almost like a heartbeat, in the fuel gauge. Turns out as the pump would attempt to force fuel to the carb, the open valve allowed it to be pushed back into the tank, which made the fuel level fluctuate, which was indicated on the gauge itself. The diaphragm of the pump was in good shape.
Only after tearing it down did I realize I might have been able to fix it. Still, 20 dollars was not money wasted for peace of mind.
Here are pics of the broken pump, as well as when I reseated that valve. You can see the rubber seal in the first pic is not set right, and in the second the tabs of the valve poking out from the hold down bracket.
