83 to 85 GPz750 Carbs Leak

I've got two 85 GPz750's that leak a small amount of gas out of the #1 carb if they are left on the side stand for an extended period of time. I've done carb rebuilds on both, Mikuni BS34s, set and verified the fuel bowl levels, but continue to see this issue. No issues on the center stand. In fact if I just put a small piece of 2x4 under the kick stand, no issues. They don't leak continuously which I suspect means the needles on the float valves are doing their job. Once it piddles on the floor a bit, it stops and doesn't do so again until it has been running. It behaves as though fuel from carbs 2,3,4 is trickling into the #1 carb and leaking out the airbox boot. Is this a model specific issue because of how it leans over on the kickstand or does there have to be an issue with float levels or...???

Any thoughts here would be appreciated.

Ive been having similar problems,only mine was on the No.4 carb. The bike would be fine for a couple of weeks then just let go,petrol all over the engine and floor. (Lucky it went out the air filter and not into the head). Anyway,the fuel tap (vacuum tap/CV carbs) was jamming open. I think dirt from the tank keeping the diaphram open.
The problem is,after any work,It would be a couple of weeks before I would know if I fixed it or not. A real bugger of a problem. In the end I fitted 4 new sets of float needles,cleaned the tank(again) and cleaned the petcock(again) after fitting a rebuild kit.
There was a very good tutorial on petcock overhauls from an XS 650 site Theres a link to that in my thread somewhere and elsewhere on the forum. Try the search engine.
Its now 3 or 4 weeks since I last did mine and so far,no leaks. Fingers crossed!

Sounds like the fuel level is too high and/or there is poor sealing on the float needles and seats. Mikuni doesn't sell float needles alone, you have to buy them with the seat. They are not cheap but in my experience the real Mikuni parts are superior to most of the cheap aftermarket "carb kit" junk there is on the market. For example, many if not most aftermarket float needles have weak springs that won't hold up the weight of the float. The proper Mikuni float needles will though. Amazon is a good place to find those Mikuni parts. You just need the part number from some place like Jets R Us.

Thanks Ed. I've reused the hard parts on this last carb rebuild. Only replacing the gaskets and o-rings with Viton o-rings. Magnified inspection of the current set showed only the slightest signs of the needle being affected by the seat. Checking the fuel level is very easy, but getting it set to the exact level you want is tedious. I may just move them all down another MM or two. See if it resolves the issue without affecting performance. Speaking of tedious, carbs on and off repeatedly is all of that. Thanks for your thoughts.