Motorcycle Leaking Fuel (1999 CBR600 F4)

Question

Just fired up my motorcycle after 3 years in storage. Changed the oil and replaced the fuel in the tank. It starts easily. It is leaking fuel from somewhere under the gas tank. The engine has a caburetor (not fuel injected). Some reading tells me common problems are dry o-rings or gummed up carbs causing them to overflow.

Is there anything I should try before starting the daunting task of dissassembling the carbs?

(replace fuel filter, fuel additives, run the bike for a while?)

Answer 1

You said that it is leaking from somewhere "under the tank" and then jump directly to the carbs. If it is the carbs, you'll probably have to tear into them.

If it is from under the tank, there are a few things you can check:

1. Is the tank intact? You may have rust burrowing through the tank and causing leaks. This is bad. Should be visible in the fuel coming out of the petcock.
2. Are the fuel lines intact? The rubber fuel lines can dry-out and crack pretty quick.
3. Is there any leaking at the petcock? Depending on the design of your CBR, there may be a vacuum-activated petcock, inside of which the membrane can dry out and crack, causing leaks. Or the seal between the petcock and the tank has cracked.

That should give you somewhere to start.

Answer 2

I would get the tank up and take a very good look around for the leak. Does it only leak when running? That may give you a clue as to whether it's tank or carb related. The chances are that it'll have a vacuum activated petcock as Jack M. mentions above. They can stick open and allow fuel to flow all the time into the carbs, whcih then overflow into the crankcase. You can open up the oil check port and sniff to see if that smells heavily of petrol, that would indicate that the carbs are leaking the fuel.

Another trick to try it to get the tank off and wrap a little rag or paper towel around each joint in the fuel system and then leave it for a bit. Then go back and inspect the towel for petrol. the towel should be soaked if there's petrol leaking. (I also do the same trick when working on any home plumbing to make vey sure I've not left a slow leak in any joints)