MKII fuel cap issue

Just finished my bike and after I ride it, the fuel tank hisses from the cap. Some fuel had splashed around inside the tank and spit out the cap. Got under the paint and screwed up my new paint job. Needless to say, I'm pretty pissed. Where is the vent on a MKII tank?

The vent is probably built into the cap. If it is hissing the vent system might be getting plugged up. Take the cap apart and inspect vent holes, passages, and gasket.

Also I recommend never filing tank more than 2 inches from top. I have seen a couple of my lacquer paint jobs ruined from sitting in the sun on the side stand with a topped off tank. Urethane clear is a lot more fuel resistant.

Noticed my tank doing the same thing. when using the kick stand gas started coming through the keyhole?! My searching shows to check the pin hole vent and make sure the rubber seal is still good.

PaintWorkz wrote: The vent is probably built into the cap. If it is hissing the vent system might be getting plugged up. Take the cap apart and inspect vent holes, passages, and gasket.

Also I recommend never filing tank more than 2 inches from top. I have seen a couple of my lacquer paint jobs ruined from sitting in the sun on the side stand with a topped off tank. Urethane clear is a lot more fuel resistant.

Good advice, esp. the overfilling.

Think about it folks. If you fill a fuel tank up to the very top with cold fuel that came from tanks underground at the gas station and then have a hot motorcycle engine sitting directly under the fuel tank and/or the sun warming up the tank from above the fuel will expand some as it warms up. Under those circumstances the expanded fuel is going to come out either through the vent, the carbs, or a weakness in the tank itself. Ed

I bought my MKII with 500 miles on it. The cap would always leak all over the tank if ridden anywhere near hard, and leak while stopped, sometimes would leak all over while stopped even at 1/2 full. The cap is vented through the keyway just for info. I replaced the gasket and made sure venting was working through the cap, and even though these items were fine, the cap still leaked. I boought a new Kawasaki cap and no change. The cap just plain leaks. I even saw goofy things like sitting on sidestand in sun and leaking uphill on the tank. It's really a bad design on the cap is all I can say, as I never had any luck in 80,000 miles trying to make it not leak, but thankfully would never consider repainting, so nuisance was purely wiping off fuel spills constantly.

Are you sure your MK. II gas cap itself is leaking?? Kawasaki had a service bulletin on fuel leakage from MK. II gas caps. It was not the caps them self, the fuel leakage was coming from the two 5mm screws that bolt the gas cap to the tank. When I first put my MK. II Superbike together, I did have fuel leaking around my gas cap!!!! Kawasaki in their service bulletin told you to use two new o-rings that fit into grooves on the bottom of the mounting bracket of the gas cap. Then use a sealant on the threads of the two 5mm mountings screws and their plastic sealing washers to keep the fuel from coming up the threads. The bulletin also stated to make sure there was no type of paint on the sealing area where the rubber gasket of gas cap would come in contact with the tank. Plus it said never fill tank any higher than that inner lip that is about 3/4 of an inch below the top of fuel tank.

I went a step further than the service bulletin said. I used TB-1211 sealant on the o-rings, the two 5mm screws, and on the plastic washers that fit around the two 5mm screws. Then let it set up for 2 days or so before putting fuel back in tank. After doing this, my MK. II fuel tanks NEVER leaked a drop of fuel ever again!!!! I have always run my MK. II's on race fuels like VP's C12, or UniCal leaded 105. In real hot weather a fully filled fuel tank with race fuel would expand so much that the caps actually hissed!!!! But no fuel leaks!!!

The inner lip I am talking about can be seen in this photo. The white coating is Kreem coating I did back in 1979!!!!

Notice there is no paint on the sealing surface where the gas cap rubber would touch the tank.

You can see some of the TB-1211 sealant oozing out from under the cap mounting bracket.

That is crazy that KHI designed the screw holes right into the tank.....what were they thinking!

PaintWorkz wrote: That is crazy that KHI designed the screw holes right into the tank.....what were they thinking!

Most Kawasaki models in the early 80's used gas caps with the same style mounting!!!!!

The ELR's, GPz's, and the KZ1000 J models had the same style caps.

If you seal up the screws, most of the time they don't leak!!!!