1983 kz550 LTD C Petcock positions

Recently took my bike to a mechanic to have the fuel delivery and electrical looked at. Apparently, The PO seriously molested this thing. Some how I managed to not screw it up with all of my tinkering. *wipes brow*

Mechanic Replaced the petcock line. Prior to this, the bike wouldn't start on any other position than PRIME. It would run, but crumby if I switched to ON after starting the motor. Mechanic said "You should never have to use prime. prime is for me."

My understanding prior to him saying this was that prime could be used to get the bike started. Can anybody shed light on this?

Thank you!!

PRI prime position is supposed to always allow fuel to flow through the petcock, vacuum being irrelevant.

Other positions (ON and RES) are supposed to allow fuel to flow through the petcock only when vacuum is being supplied to the petcock, such as when the engine is running or is being spun over during the process of being started. There are several conditions that could result in lack of fuel flow through a vacuum operated petcock in the ON position or in the RES position.

Vacuum hose should be in good condition, unobstructed, un-kinked, clear, and with no leaks (snugly attached at both ends, and no cracks). Being readily available and very inexpensive, if in doubt, replace the vacuum hose with a brand new one.

Good Fortune!

Patton,

So in layman's terms: Using PRIME to get the bike running and switching back to ON is acceptable and will not damage anything?

Mechanic said "You should never have to use prime. prime is for me."

That's bs. The fuel level in the carbs can be low from evaporation or if you run out of fuel, so at times you may have to set it to prime for a minute or two prior to starting the bike. If the fuel in the carb bowls is low, it can take a little longer to start the bike. I use PRI regularly to ensure fast starting.

ON = normal riding position. engine vacuum actuates a spring loaded diaphragm to allow fuel to flow by gravity. when the engine is stopped, the spring returns the diaphragm to the closed position.

RES = reserve. switch to reserve when the fuel is low, then fill up the tank ASAP, within 10-20 miles or so. operation is the same as ON, except it uses the remaining 0.5 to 0.7 gals of fuel.

PRI = prime. bypasses the diaphragm assy. allows fuel to flow by gravity, engine running or engine stopped. operating the petcock while the engine is running doesn't hurt anything, but don't leave it in PRI or RES, as you could run out of fuel unexpectedly.

LesbianSeagull wrote: . . . So in layman's terms: Using PRIME to get the bike running and switching back to ON is acceptable and will not damage anything?

Won't damage anything.

The petcock has an intake tube extending up inside the fuel tank that quits feeding fuel when the tank level gets low, which tube is operational in the ON position. In RES position, all fuel will feed from the tank, from full to empty. Both ON and RES positions require vacuum supply.

In PRI position, all fuel will feed from the tank, from full to empty, without requiring any vacuum.

Accumulation of dirt or crud inside the petcock can obstruct the spring loaded diaphragm and cause the petcock to malfunction. Sometimes disassembly and cleaning of the petcock will restore it to serviceable condition. Other times, replacing the diaphragm and o'ring is also necessary. If needed, Z1 Enterprises offers petcock repair kits.

Good Fortune!

Cool! It's confusing getting different information from just about everyone I talk to.

Martin and Patton, your input is greatly appreciated and has helped me with alot on this bike, since I began posting and reading the site. You guys kick ass.

Thanks again

Another reson to use PRI. If the bike sits unused for extended periods (2 weeks or more), especially if the weather is hot, you can use PRI to drain the stale fuel from the carb bowls. set it to PRI, then open the float bowl drain screws. The fuel in the tank stays fresher longer as it's typically a much larger amount. After draining, sometimes you can detect the difference between the smell of the old fuel & fresh gasoline. old fuel can have an odd odor.