Lean dilemma

So I have a problem with my KZ650...

First off some history. When i picked it up, the owner had installed a plastic on/off valve below the petcock. Why? According to him, the no.2 carb would overflow and spill gas out of the overflow tube on the bottom of the bowl. He also mentioned going into the no. 2 carb because of that very reason.

After getting it home, I soon discover that the petcock is frozen to "on". Now after a month or so of ownership, ive noticed a few things here and there, like a soft misfire while cold, choked and warming up. This would appear to clear up after it was warm, but i would notice if i was slowing down with engine braking, the exhaust would give off a crackling noise like there was extra fuel being burnt in the exhaust.

Last night, me and couple friends were shooting the shit while I sat on it waiting for it to warm. With the choke on about 50% my friend quickly told me that the exhaust off of cylinder 2 and 4 were glowing red hot. I immediately turned the hoke off, the idle smoothed out (that soft misfire started to clear up) and the two headers cooled down to match the other two.

Today, i was out riding it and at highway speeds, i peaked over for a second and noted that the no.4 cylinder... again was running incredibly hot. In the sunlight i could see that it was red, but in small spots of shade, you could definitely tell the exhaust was extremely hot.

My thoughts are, with the petcock frozen, whatever is in that that to make the lever stick could be breaking off and going into the carbs and clogging up jets. Also, the fact that this guy said he went into the no.2 carb specifically and thats one of the cylinder running hot, makes me thing he messed up the jetting. On top of all this, there is a Vance & Hines 4-1 but the OEM intake box and intake assembly are still equipped. With that in mind, this also makes me think that the carbs again, are jetted incorrectly and i could probably have cylinders 1-3 running rich and cylinder 2-4 running lean.

Thoughts?

Assuming your bike has the stock petcock there should be a vacuum line running from the #2 carb to the petcock. If that line is not there, and if that vacuum port is open (it would be forward of the vent port on #2 carb) the #2 carb will be drawing in raw air which can cause a lean condition for that cylinder. If the vacuum line IS there and the petcock is screwed up (which you indicated is the case) the petcock can allow fuel to pass through that vacuum line which can cause a rich condition in the #2 cylinder. Either problem should be fixed. You should rebuild or replace the petcock as the first step. Second, I would make sure the carbs are all jetted to the stock settings. I also would clean the carbs and ensure they are not overflowing. The overflow condition will result in fuel inside the crankcase which will corrupt the oil and cause internal problems. Ed