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Louie, Technician
Category: Motorcycle
Satisfied Customers: 11943
Experience:  25+ yrs. experience
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198 nighthawk SC700S. fuel will not flow through petcock at

Customer Question

198 nighthawk SC700S. fuel will not flow through petcock at bottom of tank. I have removed petcock, sediment bowl is clean, no dirt, rust ,nor small particles. can not force air through connection to carbeurater fuel feed line end of sediment bowl with bowl on, air flows fine with sediment bowl off. When on/off/res is switched from on to res and back (through off posisiton), a small amount of air can flow for a short time only then stops, near the off position (not at off). Rust in valve? Fuel drained from tank (not much) appeared clean with no rust specks observed.
Submitted: 7 months ago.
Category: Motorcycle
Expert:  Louie replied 7 months ago.

Hi, I’m Louie. Sorry you had to wait awhile but I’ll do my best to help.

Initially, can you please post a clear picture of the petcock? Click HERE.

Also of interest would be the back.

Expert:  Louie replied 7 months ago.

Depending on the version/petcock, it is possible that the vacuum activated valve has an issue; either no or weak vacuum or the vacuum valve itself has failed. This vacuum activated valve is responsible for automatic On/Off of the petcock depending if there is vacuum/engine is running.