Motorcycle Repair: V-Star stalls out at high speeds, volt power supply, yamaha 650 v star

Question
I'm stumped I don't know much about my motorcycle, but I thought I'd give it a whirl if it was something simple.  I ride my 1998 Yamaha 650 V-Star about 80 miles 3 to 4 times a week and suddenly it stalls out at speeds around 70mph.  It'll only restart with the choke completely opened up and if I stay at low speeds I can get it back home.  I've drained the fuel tank--didn't notice any particles. When I drained the tank the fuel only ran freely while on reserve, but completely stopped on the "on" position (is the fuel sucked out with vacuum pressure on the "on" position?) so I removed the petcock--the filters look as good as new but I ran carb cleaner through it anyway. I changed the fuel filter and the air filter and.....it's still stalling out!! Any advice would be appreciated.

Answer
Hi Michelle!!

Well, I'm impressed that you had the good sense to get this far in diagnosing the problem. You are on the right track. I too would suspect a fuel delivery problem is to blame. Near as I can tell, the petcock is not vacuum operated. The reason you are not getting flow from it except in the reserve position could be because the fuel level in the tank is to low to feed the "on" tube... so fuel only flows when placed on reserve. I would be more inclined to suspect the fuel pump (or fuel pump relay) is acting up. On your bike, a fuel pump forces the fuel from the petcok to the carbs. The fact that it will run fine at low speeds but not at higher speeds indicates that the pump is not pumping to capacity. The only good way to test a fuel pump is to remove it from the bike, rig it with temp hoses and measure the amount of fuel it pumps over a period of time. You need to rig a 12 volt power supply to the pump (hence, a shop manual will be needed). Put the intake hose into a container of gas and use a measuring cup/container to catch the gas from the output hose. run the pump for 5 seconds. Now look at how much fuel it pumped out during that 5 seconds and multiply that by 12 to determine the flow capacity. A good pump should deliver approx 800cc per minute. If yours is drastically lower, then the pump is the problem. And Michelle, if you decide to do this test, PLEASE be careful as gasoline can be ignited by electrical sparks. Do this test in a well ventilated area away from other combustables and make sure you have a B/C rated fire extinquisher on hand... just in case. Good luck and let us know what happens. Ride Safe!!

Jack