Back in Dec.09 I posted a thread "Leaking fuel when on the side stand", and received many good Ideas, I was prepared to remove and check all the floats, valves to find the bad one. I have ridden a few times since I had the leaking and used the side stand to try and see when/where/ temp etc. it was going to leak, well it didn't, at least when sitting for short periods of time, 15 mins to 45 mins.
Well today went to club meeting at about 9:15, lasted until 12:00PM so bike was almost cold when I got back on it. I had filled up prior riding to the meeting which may relate to the problem. It had been sitting on the side stand and no fuel was leaking, so I was a happy guy until it wouldn't start. With choke on, it would try but start, acted as if it was not getting fuel or flooded (can have similar symptoms). So then I tried with no choke, no real difference. I opened the tank and closed it, all seemed OK. While I was doing the checking tank and trying to start now it was on the center stand. After a few more attempts, with and without the choke, it started and acted normal.
I left and rode about a mile, stopped at a light and it started idling slow then wouldn't run, pushed it off the road, put it on the center stand, opened the tank again, and in a few minutes it started and ran fine the 13 miles home.
This seems like a simple case of not venting properly, right. Well about three weeks ago I made a 160 mile run with 30 other bikes, about the same conditions, tank full, and had NO problem. We were, at times, running 130 + mph, if there was a venting problem I would think that is when it would show itself. It ran fine, I could eat everything else that was riding, 600s, etc except the 2 busas. My point is at that rate fuel venting should have been a problem.
It seems that the venting issue is only a problem if bike has been on the side stand, maybe, still not positive venting is the problem.
Didn't have time to pull it apart and check out anything today, so I came here for some ideas. I did check the oil and no fuel is in it.
Has anyone had a tank apart for any reason that may know what the venting system looks like or had any similar problems.
I am looking for ideas and places to look for this " sometime" problem.
I know that there some GREAT minds here (well at least one or two,lol) and really have to get this issue resolved so I can depend on the bike.

 

Mine started to leak from under the plate on the front underneath the tank - where the mounting plate is welded. I had to have it coated to resolve the problem - the vent is a thin pipe that runs from under the tank to a position behind the filler cap, and reaches almost to the top of the tank. You can try running a thin piece of wire up it but be careful - don't break the wire in the pipe or you'll have plenty of problems !
I would say that you may have two issues,
1 a seam leaking on the tank (happens quite often on the older ones)
2 an intermittent blockage somewhere ..........

I'd suggest removing the heat shield under the tank and looking for seepage
(mine also didn't leak when less than half full)
Run some carb cleaner through the bike - added to the petrol.
Check the routing of your choke cable...........
It COULD be an intermittent fault on your kill-switch - or the sidestand switch...I had that happen to me..........

TRY LEAVING THE BIKE ON THE CENTRE STAND - let's see whether angle or sidestand switch has anything to do with the problem.

Let me know what you find, and we'll go from there.....

 

Shadow, thanks. I have tried all those things, and more. If I park the bike on the centerstand I don't have the issue. This is a fuel issue, either too much, or not enough connected to a venting issue. While running the starter it will try to start and sometimes does start, but if U open the throttle any, it will die, with or with out the choke.
I really think it is the vent. But I will recheck almost everything.

 

I would think that running at high speeds (high RMP's) would say "no venting problem". If it is leaking on the side stand and hard starting, I still think the needle or needles are sticking or the floats and letting to much fuel in the bowls. There may be just enough to run at high speeds but to high of a bowl level and spills out into the carbs when on the side stand. After hard starting (just cranking not running), have you pulled the plugs and checked them to see if they were wet?

 

here is what i believe to be your problem. i have an 87 1000 witch had the same symptons. i am a diesel\tractor trailer mechanic by trade. on most bikes all the fuel contained in the carbs is all in the float bowl. on cbr,s part of the fuel level extends above the float bowl into the carb body making the carb body part of the bowl or vice versa. on my bike the float bowl o rings were leaking very slightly, not enough to drip as the fuel evaporated as quickly as it leaked. eventually the fuel would drain from the carbs and the supply line from the pump and presto the bike would be very hard to start. here,s how i fixed it. new o rings for the bowls are not available from honda and are quite expensive in the carb kits i have seen. i bought gasket material from napa and traced and very carefully made gaskets to seal the bowls. this corrected the problem. hope it helps