kz550 A2 stalls on highway run

Also, even though the petrcock takes a key, it is not "keyed". Pretty much any key that fits in far enough will open it.

I doubt it's a float level issue. That would show up anytime you were accelerating hard. Because it's a sustained speed issue, I think others had it right, it's a fuel delivery issue.

Have you taken the petcock out of the tank and inspected the internal screen filter as GPZ550D1 suggested?

Also, don't use an inline paper car filter. Those have been problematic.

As was mentioned, rule out the tank vent as a possibility.

Well i drove it today on the highway with the cap open and the problem was gone. There is some kind of build up where the vent hole is. I am going to take it apart tomorrow and give it a good cleaning.

On another note, the petcock does not turn off. I pulled the fuel line off and it never shut off. It flows the most on prime, but still comes out on res and on.

Will cleaning the petcock fix this, or do I need a rebuild kit? I am new to vacuum petcocks.

Thanks again

You probably need the rubber seal for the inside of the lever assembly. That's the round part that has four holes in it. I don't think I've seen them available separately, but they do come in the rebuild kits.

(It should turn off in "on" or "res" position with the engine stopped.)

shizzomynizzo wrote:

...petcock does not turn off. I pulled the fuel line off and it never shut off. It flows the most on prime, but still comes out on res and on.

Will cleaning the petcock fix this, or do I need a rebuild kit? I am new to vacuum petcocks....

Would disassemble, inspect, and carefully clean.
Might find grit or crud impairing the diaphragm action, 0-ring, spring, or position gasket.

But the diaphragm or 0-ring or gasket may be damaged beyond further service.

If parts look okay, reassemble and see what happens.

Good Fortune!

I'm going to try and run most of the gas out before I remove the tank and tinker with the petcock. The inside of the tank is spotless, but I'm sure there is some build up of crap on the screen.

I looked at the bike after I was done riding it and there was a puddle of gas below it. The #3 carb started spewing gas and it has not done this before. I tried tapping it with a screw driver, to no avail. I loosened the screw to empty the bowl, let it fill and emptied it a few more times and it stopped. I hope I don't have to remove the carbs again, they are a real PITA!! well at least compared to my honda.

Thanks for all the help guys!

Sounds like were able to flush away whatever grit or crud was impairing the float valve function.

Hoping an inline fuel filter is fitted.

Good Fortune!