So I recently bought an 87 CBR600F and have had a consistent leak from the overflow tube between carb 3 and 4. I have disassembled the carbs MANY times, cleaned them, set and measured the float heights, replaced the needles and seats, re set the float heights higher (to test) and nothing seems to permanently fix the problem. If I rip apart the carb and adjust the floats (up or down) and then put it back together everything is fine for a day or two. It's only after 3-4 days the carb starts leaking (spewing a steady stream) again. I've had this bike apart 15+ times and am starting to lose hope. The last thing I can think of that it could be is that my petcock is missing the **** so I haven't been turning off the fuel supply when it's not running. Could this be slowly leaking through the pump and flooding the carb? That would explain why after opening the carb and draining the fuel it stops for a day or two. I plan on replacing the petcock anyway but I really want to figure out the leak and fix it. Thanks in advance for your help!

 

I can leave my petcock open indefinitely and it never leaks into my cylinders or out the overflow. You said you replaced the needles and seats and adjusted the float height so as long as those are good it should be ok. One thing I would check is to take all of the floats out and shake them to see if its slowly filling up with gas from a crack or pinhole. If its filling up it will drop and open up flow

 

Thanks for the response. I checked the floats and they're empty, I also held them submerged for 30 or so seconds to look for bubbles and they seem to be airtight. I've checked and re checked the float heights but short of rip it apart every time I want to ride it I don't know what to do.

 

I'd check all your orings at the "T's

one if these can take care of leaking petcocks

 

Man that's weird I was for sure it was a bad float when you said it takes 3 to 4 days to start overflowing

 

Maybe leak is the wrong word, it's a steady flow of fuel out of the overflow tube. I did check the o-rings a while back and actually did replace them but it isn't leaking from the base of the T it's coming straight out the tube.

 

Bad fuel pump perhaps. It has an auto shut off feature that turns itself off at 6psi. If it was broken it could continue to pump past that point, opening up the float by sheer pressure.

Bypass the fuel pump and run your fuel line as gravity feed to the carbs inlet. If it continues to leak it is something else. If it stops, well, There's your problem

 

Yeah i thought about that too. The pumps seem pretty hard to find also so i hope that isnt it. I imagine not, but would a gravity feed to the carb be enough to ride with?

 

I found a new pump on ebay so I ordered that and we'll see. I'm also going to extend the overflow tubes and route them out the bottom of the bike. I have no idea why that wasn't done that way from the factory. It makes more sense than dumping excess fuel directly onto the engine and exhaust.

 

2 things. 1) it usually doesn't dump fuel 2) there should be a catch that funnels the fuel into a drain, exiting near the right rear set, IIRC