Gas coming out the tank cap? WTF?

Hello, all.

I need some help. Yes, I've searched the old posts here.

My 1997 KZ1000P runs just fine, except for one thing: recently, gas started flowing out of the filler cap while riding and after riding while it's parked in my garage. The flow is small enough that it evaporates before it runs off the lower edge of the tank. This happens even when the tank is less than half full. How is this possible? Bike mechanic says I need a new gas cap. OK, but why? He doesn't really know, just says the seal and other rubber parts there are shot.

Cheers,

Dave

You can get a new gasket for the cap, from z1enterprises. Then I would disassemble the cap, and make sure the vent holes are clean.
You could also add some heat shielding to the bottom of the tank. Many later bikes have this stock, not sure about yours being a cop bike. The auto stores or online for the insulating shielding.

I would take a close look at the cap to make sure the vent is not obstructed, clean the vent if necessary, and replace the rubber gasket. That should solve the problem. Ed

Thanks, gents. Will do.

Still a mystery how gas could flow uphill. You'd think a pressurized tank would tend to overflow at the carbs or into the airbox. The oil is not contaminated, so it's not getting into the motor.

Dave

I wonder if it is fuel that splashes up into the cap internals and when you shut the engine off pressure (from the hot engine heating the tank) pushes it out the vent? Ed

I don't know the style of cap used on your police bike, but if it's the rectangular piece of junk as used on the 79/80 MKIIs ect, they will always leak. The vent through the keyway in the cap will condense gas and gas will run down your tank. Actually I've even sat on the sidestand in hot weather and due to fumes going uphill actually had gas running "uphill" on the tank. I replaced the gasket, then the whole cap to no avail. Bad design on that rectangular cap.

RonKZ650 wrote: I don't know the style of cap used on your police bike, but if it's the rectangular piece of junk as used on the 79/80 MKIIs ect, they will always leak. The vent through the keyway in the cap will condense gas and gas will run down your tank. Actually I've even sat on the sidestand in hot weather and due to fumes going uphill actually had gas running "uphill" on the tank. I replaced the gasket, then the whole cap to no avail. Bad design on that rectangular cap.

It is not a bad design and seal well as long as all the rubber pieces are in good condition. I have the retangular one on my ELR Clone, 82 GPz750 tank. It too leaked and I fought it for about 1 year. I replaced the large rubber gasket with a new one and it still leaked. The vent holes were clear and working correctly but it still leaked. Found a small rubber o-ring that seals the key tumbler all cracked and falling apart. Put in a new one, I have no leaks now. You have to completly take the gas cap aprat though to get at it. The o-ring is nothing special, I just took it down to the hardware store and found one that was close, $.57 and leak fixed.

I never could make that cap work on the MKII, just got used to it. The motorcycle had 500 miles on it when I got it, has 80,000 now and it's leaked for 79,500 miles so far despite replacing the seal on the old cap and even replacing the entire cap with a brand new Kawasaki cap. I found I could minimize leaking by never hotrodding the bike if tank was more than 1/2 full, and never park in the sun, but if parking in the sun was unavoidable, make sure tank was less than 1/2 full. Even at 3/4 full, in the sun, gas would leak.

Gents;

Yes, it's the rectangular cap.

I replaced the entire cap with a brand new one from Kawasaki that is chromed, not black like the original. The problem is solved. My garage no longer smells like gas and there are no dribbles on the tank when parked in the sun. And, my fuel economy is back up to 42 MPG on regular Chevron (was down to 30 MPG during the leaky time).

Cheers,

Dave

Dang I wish I would have seen this sooner, just went through this on my KZ1000. There's a small o-ring inside the vent that gets squished and rotted, I replaced it and everythings good now (it's about the size of a dime.)

DesertKZ wrote: Dang I wish I would have seen this sooner, just went through this on my KZ1000. There's a small o-ring inside the vent that gets squished and rotted, I replaced it and everythings good now (it's about the size of a dime.)

Where'd you get the replacement o-ring? How about the dimensions? Thanks.