Gas smell; dirty residue on underside of tank

[oldandslow]

Hi All - Thanks in advance for your help.

A couple of months ago I began noticing a gas smell by my '02 B12.  This occurred when the bike had been parked (all day at work, or overnight at home).  The bike is outside in both cases.  Same situation, every day since then.

More recently the smell got worse, and I began noticing it while riding, which I hadn't previously.

I inspected the bike and found the underside of the tank to be coated with a dirty residue that smelled like gas.  Mostly on the left side, right above the petcock.  Plenty of residue on the leftmost carb and adjacent hoses.

Lifted the tank and inspected further.  Could not see anything resembling a drip, but it sure is dirty under there!  Most of it wiped off with a paper towel.  Cleaned the rest with Simple Green, toothbrush, and a hose.  Dried it off and let it sit (warm, breezy day), then started it and let it idle for a few minutes.  Switched off and inspected the underside of the tank, petcock, and hoses.  No sign of a leak.  I'll keep checking it each day - maybe it's so slow it will take a while to show.

After cleaning, I couldn't really tell if the gas smell was gone, because by now I reeked of gas :(  but I *think* it smelled less.

I searched the Forum and read all the posts about bad petcocks, running rich, etc., but none quite seem the same (apologies if the solution is out there and I missed it!).  I don't believe there's gas in the oil - oil level drops slowly, consuming maybe a quart in 2000 miles, same as it has for a while.  I don't think the gas smell is from the exhaust, since the smell is evident when the bike has been off for hours.

Any ideas what I should check next?  I suppose I can just replace the petcock – they seem to be a weak link – but hate to do that until I've reasonably diagnosed it as the culprit.

Other info:
- '02 Bandit 1200, purchased new/leftover in '03.  California model. Sole owner
- 28K miles
- Generally ridden daily (35 mile R/T commute) – ridden conservatively
- All stock engine, carbs, exhaust
- Carbs have never been touched – the bike fires easily on the choke, and can be ridden immediately, even on cold days, so I've chosen not to mess with it;  Probably coud use adjustment / synch.
About 38-40 mpg consistently – I think it should be better - a synch might help
- Last checked valves and plugs at about 13,000 miles – both were good (yes, I know, it's time to check them again; might account for the poor mileage, but not the gas residue on the tank underside....I think)

Thanks again!
Rob in Half Moon Bay, CA

[pmackie]

Check the two hoses that connect to the tank at the RH rear. One is the overflow drain tube, the other is the tank vent. If either is missing or the hoses and/or tube cracked, you might be getting some fuel collecting on the bottom of the tank and then moving around.

While you're there, check the fuel level gauge sending unit for leaks.

[txbanditrydr]

Check the breather hoses that run beside the airbox on either side - especially the left side.  They terminate at a tee connector that spans each pair of carbs.  They (the tee connectors) may be rotten or otherwise cracked.  Mine were - only recently found them when I installed a jet kit and pulled the carbs (first time).  FWIW - my left side carb was covered in gook just like you describe.

[PaulVS]

Give it another month and let us know what's on the underside of your tank.

[oldandslow]

Update - after cleaning the area and then riding for a week the residue has reappeared.  It is on the underside of the tank right behind where the petcock bolts to the tank.

From looking at Bike Bandit's diagrams, I'm guessing it's the gasket:
O RING,JOINT 499433-001  -  $4

Anyone else have this part leak?
Thanks!
Rob

[PitterB4]

Sorry I'm just reading this thread for the first time...  From the start, I was wondering if the petcock gasket was bad.  I assume you've tried just tightening the bolts on the petcock.  I was also wondering if you had any rust in the tank?  You could have a pin-hole leak.  I hope its just the gasket.  Keep us posted. 

[oldandslow]

No, hadn't tried tightening the bolts on the petcock yet - good suggestion,  !  I'll try it this weekend, clean it again, and observer for another week.

The bike rarely sits, so I'm hoping that rust is unlikely

Thanks again!