kz550 A2 stalls on highway run

Hello,

I have an 81 kz550. I drove it over a friends house and it sat for about 3 hours. Then I headed home. I let it warm up a bit (3 or 4 minutes) and then headed for the highway.

I wound her up on the entrance ramp and got up to about 90 (it burried the needle, so I don't know how fast for sure). I slowed down a bit got over and then after about 1/4 mile it began to die out. I kicked the petcock to reserve, but no difference. I was down to 45 about now and decided to kick on the choke, and it breathed a little life in her.

It was sputtering... speed up for a second, then bog down for a second, repeatedly. I felt like I was on one of those "penny pony rides at meijer". I was able to get off the freeway at the next exit, and then it stalled completely. I kicked the petcock to prime, and turned the choke on and she fired right up. Turned the choke off and it drove fine the rest of the way home (took side roads)


I cleaned the carbs and bench synched them a few weeks back, but still waiting on the carbtune to arrive. I didn't touch the floats, but the slides in the carbs were way out of wach when I cleaned them. I couldn't find a measurement of what height to set floats so I left them alone (they were all even).

After searching the forum, I am going to check the gas cap vent to see it is clogged in any way. Is there anything else I should look at?

Sounds like the gas cap vent to me

If it runs okay in the prime position, would consider that your petcock may need to be rebuilt, or the screen inside the tank is partially stopped up. Just sounds like a fuel starvation issue.

Also, check for a crack in your vacuum hose that goes from the carburetor to the petcock.

GPz550D1 wrote:

If it runs okay in the prime position, would consider that your petcock may need to be rebuilt, or the screen inside the tank is partially stopped up. Just sounds like a fuel starvation issue.

It runs just fine in any position while on city streets at speeds under 50 mph. I have not tried it on the highway, I am kind of afraid to. Near my house, I have to go about 6 miles to the next exit once I get on, and just don't want to stall out get hit or anything.

I have a keyed gas cap, so I cannot open it up while driving but I can open it before.

Does this sound like it could be a float level issue?

I have adjusted floats in my honda's carb, but I dont understand the process for this bike. On my honda it is adjusted to 12.5 mm. On the Kawi you need to use a clear fuel line with marks on it or something? can someone elaborate on this or provide a link for dummies/ newbies?

Thanks again

I would first look at tank cap vent as mentioned or look for kinked fuel line. Ed

The clear tube method is similar to a water level. Unscrew the drain screw on the bottom of the bowl, you can buy an adapter that screws in the bowl or you can get the right size hose and shove it into the hole where the drain screw was. With the carbs level and on the bench bend the hose so it is vertical up and down and hold it against the carb body. When you add fuel to the carb you now have a sight glass so you can see the level inside of the carb. The level should be just under the carb body where the bowl mates to the body. I dont have a pic but its pretty straight forward

That makes a lot more sense than the clymer!

I tried reading the clymer and it's kind of hard to understand.

Thank you

Got to thinking some about this and the vacuum operated petcock. The petcock needs engine vacuum to open up the valve to let fuel flow and when you shut the engine off, vacuum goes to zero and the the valve closes. Always thought that at wide open throttle (like when he had his bike going 90 mph) that engine vacuum went to zero? How does the fuel flow through a vacuum operated petcock at wide open throttle with little or no engine vacuum present?

When the bike is at WOT, the vacuum should be at its highest leve. When you sync carbs, the higher the idle, the more vacuum on the manometers.

I would bet money on the fact that it has something to do with the vaccume line from the petcock. Had the same problem and it ended up being the vaccume line. Sometimes the cracks are small, at WOT, pulling the highest vaccume and a lot of air through the cracks, results in starving for fuel.

I also resolved the symptom by opening the choke until I got home and called myself an idiot for not realizing it was the vaccume line the whole time.

Like the guys said, check the vent at gas cap and also replace the vaccume line for peace of mine if nothing else. I got a new line for less than $5 bucks at the local bike shop.

GPz550D1 wrote:

Got to thinking some about this and the vacuum operated petcock. The petcock needs engine vacuum to open up the valve to let fuel flow and when you shut the engine off, vacuum goes to zero and the the valve closes. Always thought that at wide open throttle (like when he had his bike going 90 mph) that engine vacuum went to zero? How does the fuel flow through a vacuum operated petcock at wide open throttle with little or no engine vacuum present?

The vacuum is lower, but nowhere near zero. The petcock only needs a little bit of vac to open. (But if the vac line is leaking, like Yukabodos suggested, that could be a problem.)