Motorcycle Repair: Fuel Starvation

Question
Hi I have a Virago VX750 1992. It runs lovely until it grts to 4500-5000 RPM then its just as though it is running out of petrol. If I operate the choke it then runs OK iT SEEMS TO DO IT IN ALL GEARS. hAVE STRIPPED AND CLEANED CARBS BUT MADE NO DIFFERENCE hELP pLEASE

Answer
Peter, I am not very familiar with Yamaha products specifically, but a quick look at some online microfiches shows that the petcock/fuel valve has screens up inside the fuel tank, which may be plugged up from rust/debris or just aging components.

The things that slow fuel flow are the petcock filters and perhaps if the gas cap or venting system for the fuel tank is causing a partial vacuum at higher fuel demand situations.

If your petcock looks like this:

http://www.ebay.com/itm/like/360501250613?lpid=82&chn=ps

There is also a vacuum diaphragm line on the back side. If the diaphragm fails, you get an air leak and loss of fuel delivery.

Bill Silver