Fuel in the Airbox, 1980 Kz 1000 Shaft

I have fuel leaking from the airbox. I decided to first remove the air-suction system(A.S.S.), vacuum lines, switch etc... While removing the vacuum lines I noticed a small bit of oil at the large vacuum line connected to the airbox also. The bike is beautiful and has always ran great, what can I do? I have a service manual and am ready to tackle the problem but need to now where to start. Thanks in advance for any assistance you provide. One more thing, I was told to plug the different openings left from removing the A.S.S. with Black RTV. Any additional assistance with what black RTV is and how to use it would be helpful.

Volktron58 wrote:

I have fuel leaking from the airbox....

Would sniff-test crankcase oil for fuel contamination.

Good Luck!

........I have fuel leaking from the airbox.
There isn't supposed to be any gas in there. I can get in there in one of two ways... PLEASE don't presume you know the answer as any assumptions will cause massive wastes of time... FIRST reason is that the bike is usually parked on sidestand and when you shut the bike off and park it, the petcock misbehaves and allows gas to flow. The gas will then overwhelm the float valve(s) in the carburetors and will fill the bowls and then overflow via the overflow tubes AND the hole in the venturi... when it comes out the hole in the venturi, it will go in two directions. Into the combustion chamber and into the air box. The fix here is basically to buy a new air filter, change your oil but most important, fix the petcock problem. To test the petcock, with the bike OFF and not running (parked), just take the gas line off the petcock... if there are two, just one is fine. If gas comes out, the petcock diaphragm is defective OR the hose that maintains a vacuum when the bike is running was removed or is otherwise compromised. It will likely be going to carb #2. Carbs are counted 1 to 4, left to right as you sit on the bike. The SECOND possibility is that one or more cylinders are NOT firing and the gas that is being drawn in is NOT combusting. If this is the case, the fuel will get into the airbox during operation. Easiest way to test is after a ride, take a SPRAY BOTTLE of water or orange cleaner and spray each exhaust downtube. If the water vaporizes, the cylinder is firing. If it rolls off, not matter how hot it seems, the cylinder is NOT firing. Check it out.

......I decided to first remove the air-suction system(A.S.S.), vacuum lines, switch etc...

If you don't know what you are doing, you could harm, the bike or create a fire danger situation. STOP and read before running the bike anymore....

There are hoses connected to TWO of the three carburetors. 1 and 4 are joined at a tee. 2 has a hose running to the petcock and 3 will likely have a rubber cap on the vacuum fitting which is located adjacent to the mixture screw on the top of the carb on the engine side. LEAVE THE HOSE CONNECTED TO THE VACUUM FITTING AND PETCOCK (#2 carb) ALONE. IT NEEDS TO BE THERE. Remove the hoses from 1 and 4 and put vacuum caps on the vacuum ports. You can buy vacuum caps at ANY autoparts store. Use 3/8" and normally found on a board in a purple packaging in packs of 5 or 6. Don't use caps that are too big as they will fall off and check them regularly for cracks. Cap 1 and 4. Trace the hose back to a metal vacuum switch. Remove it and the hoses connected to the switch. Plug the holes in the airbox where hoses connected. There will be one large diameter hose connected to a tee fitting and two large hoses connected to your valve cover. Remove the big hoses. The place on the valve cover where they connected will be a metal sleeve. You want to fill these with BLACK RTV. Black RTV is essentially silicon and you can buy a tube at any autoparts store. It looks like a tube of toothpaste. They will have different colors of RTV. Black is a general purpose goop. The reason you fill those tubes on the valve cover is that if the reed valves below (essentially flappers) open, there is a direct passageway to a hole just outside the exhaust runner in the cylinder head and any backfire will result in flames coming out the metal tubes located UNDER YOUR GAS TANK. The one hose you want to leave in place is the crankcase breather hose. It is a crooked hose under the air cleaner joining the air cleaner and crank case vent. In the event you get a little engine oil blow-by going into the air box, that is normal and is as it should be. That is why the hose is routed up into the air box... so it won't drool on the road. The crankcase MUST be allowed to breather else it will develop negative pressure and ruin the engine.


........0While removing the vacuum lines I noticed a small bit of oil at the large vacuum line connected to the airbox also.

See above

George is the king of carbs, but I'll add my $.02 to the mix on the carbs leaking.
#1. It takes both a bad petcock and bad or misadjusted floats/valves to cause fuel overflow when the engine is stopped. One or the other cannot cause it if the other piece is working. The petcock can be left in prime position for years and no fuel will ever leak unless the carbs are not functioning correctly.
#2. The vacuum hose is only used as an on/off switch for the petcock. When the engine is running=vacuum=on. When the engine is stopped=no vacuum=off. You could take the entire vacuum line off the petcock and throw it away and two things will happen. You have rough running because you have a vacuum leak, and you get no gas flow out of the petcock in the on/res positions because there is no vacuum applied to it to allow gas to flow.

Ron, I have seen NEW float valves leak when overwhelmed with a gas supply left ON when the bike is parked. This is why the manufacturers put the vacuum petcock on. I suspect that the puddles on the bikes parked in garages all over the country made them think it was necessary to take the responsibility to shut off the gas away from the rider. And the effect of having an open vacuum port will not necessarily be "rough" running. The bike will generally start but idle high. Usually, you can't get it to idle under 2K rpm with a vacuum plug off (or hose off). Once you get past idle, a missing vacuum plug isn't all that noticeable in fact. I would fear the leak could eventually hole the piston. I know this because I occassionally have had vacuum plugs blow off or forgot to install them after synchronizing a carburetor assembly.

I have not had great experiences with vacuum petcocks. On bikes I have had through my shop equipped with this type petcock, about a 1/3 of the petcocks didn't work properly.