Petcock question

Which tap coming out of the petcock is for the fuel on my kz650, the bigger one or the smaller one? Also should there be fuel coming from the vacuum tap when the petcock is turned to prime? Thanks

on my 550 big one is feed small one is vacuum,and yes prime will dump fuel to carbs

Thanks for the quick reply. Anyone with a 650? because I think my vacuum is the bigger one?

Pwallace30 wrote:

Which tap coming out of the petcock is for the fuel on my kz650, the bigger one or the smaller one? Also should there be fuel coming from the vacuum tap when the petcock is turned to prime? Thanks

My understanding - - -

The larger petcock nipple is for fuel leaving the petcock which flows through the fuel line to the carb fuel intake.

The smaller petcock nipple is for vacuum supplied through a tube from the carb, which vacuum operates the diaphram inside the petcock. The vacuum tube is not supposed to have any fuel in it, regardless of the petcock setting position. Carbs take in fuel from the carb floatbowl -- not from the carb vacuum nipples.

Good Luck!

Alright thanks guys. There is a third nipple right beside the vacuum nipple on the engine, any idea what that is for?

Here's a typical setup, "yellow" being the vacuum line to petcock.

The vent hoses should be clear and routed to open air, usually around the swingarm to exit underneath the bike OR routed to underneath the seat.

The other vacuum nipples (usually four of them) are found on the carb holders OR on the carb bodies, and are supposed to be capped with rubber caps (when not being used to sync the carbs).

[Click on image for slightly larger view]




Good Luck!

Hey thanks a lot, it looks like im missing one of the float bowl vent tubes.

2 stroker wrote:

on my 550 big one is feed small one is vacuum,and yes prime will dump fuel to carbs

meant to say prime will dump fuel to carbs thru fuel line not vacuum:blush:

How long should my fuel line be (I have an inline fuel filter that is about 2" end of niple to end of niple)? Im having trouble running my fuel line without it getting pinched once I set the gas tank down in its place.

Pwallace30 wrote:

How long should my fuel line be (I have an inline fuel filter that is about 2" end of niple to end of niple)? Im having trouble running my fuel line without it getting pinched once I set the gas tank down in its place.

Length of the fuel line is not critical.

I use the small cone-shaped in-line filters from Z1E.

Would replace fuel hose with the best new line available in a supposedly "non-kinkable" type. Perhaps to be found in a bike repair shop or local tool rental agency.

For me, the automotive style is usually too heavy-duty, thick and bulky for motorcycle application.

Most of the inexpensive clear plastic line will harden after a short time, believed as a reaction from contact with the fuel. Have not yet discovered any clear line that won't eventually harden.

Imo, Tygon is the better clear fuel line, but will never-the-less harden over time.

I now use a relatively expensive "grey line" obtained from a local tool rental agency which uses it in maintenance of their motorized rental items and also in a sideline motorcycle repair business. It is touted as "kink resistant" and actually works very well and has lasted a long time and remains flexible.

Old hard lines will often kink, crack and leak, and should be replaced.

Would exercise some planning and ingenuity in routing the new lines so that gental loops are used to avoid kinking.
Imo is best to design the routing and affix the new line while the fuel tank is already mounted in place on the bike.

There's enough room under there behind the carbs to do it, even on a KZ900 with dual fuel lines from the petcock to the carbs plus the normal dual floatbowl vent lines, crankcase vent hose, and four floatbowl overflow lines, and even the dual oil cooler lines (heavy-duty style).

Good Luck!

Just open your petcock and see which tube the fuel comes out of.............chris3

I was able to get my fuel lines worked out and take the bike up and down my street for its first ride in 20 years. I still have a petcock problem though, the bike runs fine when my petcock is turned to PRIME, but when I try and run it on FUEL, it will run for 5 mins or so then the bike will shut off. Could it be that I have a vacuum problem? Also what problems will I cause if I continue to run my bike on PRIME? Thanks