Gas dripping out of airbox on KZ1100

Any ideas why gas would be dripping from my airbox? It's not too much - when it's on the center stand I might get a small puddle overnight, and it's not consistent - sometimes it does it and usually it doesn't. I set the float levels last spring and rebuilt the carbs the summer before. The engine runs great

Forgive a little guessing here, but where carbs don't have overflow circuits or where an overflow circuit is clogged, and fuel is getting past the float valve when the engine isn't running --- fuel may rise up into the carb throat and flow both ways (forward toward the engine and rearward to the airbox).

Fuel reaching the airbox may drain down through the crankcase vent hose into the crankcase and contaminate the oil. (See image below).

Fuel flowing forward may go through the intake port and enter the combustion chamber where it flushes down past the piston and rings into the crankcase.

Would sniff-test the oil and examine its physical condition to help determine whether fuel contaminated oil might be an issue. It's bad enough in some cases to cause an increase in the apparent oil level.

Where there's fuel intrusion into the crankcase, it's best imo to change the oil and filter, and correct the problem before allowing any fuel to reach the carbs.

Good Luck!

[Click on image to enhance view.]

During our carb rebuild, did you replace the float valve assemblies?

If not, I would seriously recomend doing so...

Good luck!

Thanks Patton. The oil smells OK and looks OK through the sight glass but I'm not sure if it would look different if it has gas in it. The breather seems to open into the portion of the airbox with the filter, and there is a slightly sunken portion of the floor of the airbox with a drain hole near where the breather comes in, so it seems like gas would drain out before it would go into the breather.

Is a bad float valve the only way gas could get into the air box or cylinder when the engine isn't running?

I can't remember if the rebuilding kits had both the float valve and the seat or just the valve. Whichever it had I replaced.

KYKZ1100 wrote:

...Is a bad float valve the only way gas could get into the air box or cylinder when the engine isn't running?....

If the float itself is leaking or sticking or maladjusted or broken or has lost buoyancy for whatever reason (such as becoming "water-logged"), it can fail to push the float needle into its seat, whereby the valve remains open.

Good Luck!

Thanks. I've had a problem with exhaust popping since I got the bike. I'm going to take the carbs off to install larger pilot jets to see if I can fix that so I'll check the floats when I do that. They looked good last time I had the carbs apart.

KYKZ1100 wrote:

Thanks. I've had a problem with exhaust popping since I got the bike. I'm going to take the carbs off to install larger pilot jets to see if I can fix that so I'll check the floats when I do that. They looked good last time I had the carbs apart.

Hoping the clear tube test has been done to assure correct service float bowl fuel level.

In otherwise perfect carbs, too low fuel level could cause lean condition (with exhaust popping), and too high could cause rich condition.

Sometimes, slightly enriching the pilot circuit via the adjustment screws will reduce or eliminate the popping.

Any doubt as to integrity of the carb holders or attachment of carbs (such as a loose clamp)? As an air leak could cause popping.

Good Luck!

I have done the clear tube test and floats were right on. Carb holders were new two years ago and I've only put 2,000 miles or so on them. Spent a lot of time removing and sealing up air recirculation system and other possible sources of air leaks. Have tried adjusting the air screws. Exhaust gaskets are good and seem to seal well - the last two sets have been the Yamaha fiber filled copper gaskets from Z1 and when I take them off there seems to be a good circular indentation all the way around. Bigger pilot jets is the only thing I've seen suggested that I haven't tried yet. I went from 37s to 40s when I put the turned out mufflers on but so far I haven't been able to find a larger size online.

Sounds like your petcock is not shutting off the flow of gas when the bike is turned off. I'm assuming your bike has a vacuum actuated petcock. If this is the case, the flow of gas is overcoming the sealing ability of your float valves and once the level exceeds the travel of the floats, the gas overflows into your airbox--and possibly down into your crankcase via the crankcase vent hose.
You should look at the petcock as well as the float valves.
Best of luck,
Grant.

Grantl wrote:

Sounds like your petcock is not shutting off the flow of gas when the bike is turned off. I'm assuming your bike has a vacuum actuated petcock. If this is the case, the flow of gas is overcoming the sealing ability of your float valves and once the level exceeds the travel of the floats, the gas overflows into your airbox--and possibly down into your crankcase via the crankcase vent hose.
You should look at the petcock as well as the float valves.
Best of luck,
Grant.

It makes sense that both the petcock and at least one float valve would have to be bad in order for gas to be leaking when the engine is off. I'll add rebuilding the petcock to my list.

Did rebuilding the petcock work for anyone? My kz1100 is too leaking gas into the airbox and through the float valve and seat.
Jim

My KZ 1000 did the same thing.Rebuiding the petcock helped, but what really helped was a bright,shiny,chrome Pingel petcock.bj