TOPIC:

My wife fired her KZ 550 up today for the first time in about a year. Last winter I pulled the carbs and cleaned them and set the floats.

The bike fired up immediately and ran fine until it warmed up. Then, when the petcock in the "On" position it began to rev higher...up to around 3500 rpm. Then it stalled out. While fiddling with the petcock position I discovered that the bike runs fine when the petcock is in "Prime" position. But in "On" it's unstable.

Seems to me that there is something wrong with the petcock or with the vacuum system. I dismantled and cleaned the petcock but that didn't seem to help. So...just wondering if anyone else has had this problem?

Are you positive that when the bike is running there is sufficient vacuum applied to the petcock from the carb vacuum port? If the petcock is working properly, which is always questionable with vacuum operated petcocks, then it may be a lack of consistent vacuum from the carb. Ed

Thanks Ed. No, I'm not sure. I don't know what the vacuum pressure is supposed to be and don't have any easy way to measure it. I might be able to rig up one of my synch gauges but don't know what the pressure should be normally.

It doesn't take much vacuum at all. You can get a little syringe at a drug store for a couple bucks. That will have way more vacuum than it will ever need . It's probably in the 1 to 2 psi range or less. That's like 5 to 10 cm of mercury vacuum. The bike will usually have around 20cm of mercury vacuum.

So what do you think would cause the over revving when the petcock is in the "on" position? After it revs up to about 3,500 I switch back to "prime" and the revs drop back to normal...about 1100.

Could it be when in the “on” position it’s allowing an air leak making the engine run lean?

Tomorrow when I get time I'll pull the air hose off the carbs and check it. Then maybe pull the carbs and check #4 where the air hose connects, and check to see if the choke system is functioning properly. Pulling the carbs off and putting them back on is a regular pain in the axx.

I finally got around to pulling the carbs off the bike. The air hose was fine...no blockage. But I found something interesting. All four of the choke valves had slipped out of the slot holding them. The choke lever is over-rotating past vertical, and this is what allows the choke valves to slip out.

I'm trying to figure out how to fix this problem. Has this happened to anyone else?

Does that happen when the covers are installed?

Looks like some one bent the choke leveler end stop.

Yes, I noted the bend but there is no stop on the lever so I don't think it's a problem. There is a little ball behind the lever and two indents on the inside that correspond to full choke and no choke. The lever seems to be a bit too far from the ball for it to sit in the indents correctly. Not sure why. I tried to remove the lever and rotating arm but it seems to be fixed in position.

Yes, I think it was occurring with the tops on, but not positive. I will check that when I go back at it tomorrow. I was trying to do a mech synch and having some issues so I gave up for the night.

Someone probably bent it as a shortcut to remove the choke plates in order to maintain the choke flaps. The proper way is to remove the screw on the bell crank.