gas in oil..

Info: 78 kz650

With that being said..
fuel in the oil..


when I pulled the tank yesterday, some fuel came out of the tank through the fuel line. Only a little, maybe 4 ounces. I had the petcock set to on. There is a leak in the side of my tank (someone dropped the bike at some time, and attempted to fix the crack in the tank with silicone) So, I thought it was due to the lack of a vacuum in the tank itself..

Is it a bad petcock? When I pulled the carbs yesterday there was a gas in the air box, and I had tapped the boots to the carb bodies due to the boots being stiff.. But..

Now, I had gas in the oil, the oil is dark. I am going to change the oil, and I have a petcock rebuild kit.. should I use it?

Thanks.

The 650 had both a vacuum and a regular petcock in 78. Do you have a vacuum line going to the petcock? Is there a PRIME position on the petcock? The gas tanks aren't vacuum tight, the filler cap breathes. This is necessary because the fuel is gravity fed to the carburetors. A vacuum in the tank would not allow the fuel to run down to the carbs.
If you're asking why the tank didn't empty itself when you pulled the line off with the petcock in the ON position, if it is indeed a vacuum operated petcock, this is normal as the the lack of vacuum to the petcock will cause it to close. If it's not a vacuum petcock, then you might have a clog. If you feel comfortable rebuilding it, go ahead. The bottom of the petcock comes off and inside of it is a sediment cup and a screen. You are supposed to take them off periodically and clean them out anyway. Check that out before you tear into it.
Below is the drawing from Kawasaki.com of the petcocks, make sure you have the right rebuild kit.
The vacuum petcock is on the left.

Gasoline may enter the crankcase because of a leaking carb float valve.

Regardless of petcock function, a perfectly operating float valve will stop gasoline flow into the float bowl when the fuel level reaches specification height. And this is applicable even without any petcock at all.

Good Fortune!

Like mentioned, float valves stop the gas from rising beyond the set level so with good floats the petcock could be theoretically left on prime forever and no gas would ever leak. (78 KZ650 uses vacuum petcock). It's possible for the vacuum petcock diaphram to be torn and let gas go right down the vacuum line into the engine. Also I know this has been beaten to death, the gas in the oil debate, but on the stock 22-28mm mikuni slide carbs it is near impossible for gas to enter the engine. Reason is they have a drain tube at a height considerably lower than the openings of the carb to airbox or engine. By considerably lower I mean about 5mm or a good 1/4". This is not to say a little raw gas will not possibly find it's way into the airbox, but it should be minimal if any. If a float is not shutting off and the petcock is not shutting off, that is 2 problems, then gas rises up to the overflow tube in the carb, runs out the rubber hose to the ground. You could drain the entire tank this way and have a puddle of gas 40ft diameter on the ground, but still no gas in the oil. So be sure the drain lines are not clogged for sure. I've tested this theory many, many times over 35 years and have yet to get gas in my oil. Newer CV carbs possible, slide carbs not a problem.

RonKZ650 wrote: Like mentioned, float valves stop the gas from rising beyond the set level so with good floats the petcock could be theoretically left on prime forever and no gas would ever leak. (78 KZ650 uses vacuum petcock). It's possible for the vacuum petcock diaphram to be torn and let gas go right down the vacuum line into the engine. Also I know this has been beaten to death, the gas in the oil debate, but on the stock 22-28mm mikuni slide carbs it is near impossible for gas to enter the engine. Reason is they have a drain tube at a height considerably lower than the openings of the carb to airbox or engine. By considerably lower I mean about 5mm or a good 1/4". This is not to say a little raw gas will not possibly find it's way into the airbox, but it should be minimal if any. If a float is not shutting off and the petcock is not shutting off, that is 2 problems, then gas rises up to the overflow tube in the carb, runs out the rubber hose to the ground. You could drain the entire tank this way and have a puddle of gas 40ft diameter on the ground, but still no gas in the oil. So be sure the drain lines are not clogged for sure. I've tested this theory many, many times over 35 years and have yet to get gas in my oil. Newer CV carbs possible, slide carbs not a problem.

The issue may arise when the carb overflow circuit is obstructed (which is all too often the case), and may also arise in a manual slide carb than doesn't have an overflow circuit, such as Mikuni smoothbores.

It's a good idea to sniff-test the oil between changes, especially if the oil level seems to have unexpectedly risen for no apparent reason.

Speaking of smoothbores -- on a Z1 with the stock crankcase vent hose connected to the stock airbox, excess gasoline entering the float bowl past a leaking float valve rises into the carb throat and flows into the air box, from where it flows down the crankcase vent hose directly into the crankcase.

This condition is particularly critical because it may allow gasoline intrusion into the crankcase while riding the motorcycle.

Riders running smoothbores are well-advised to assure perfectly functioning float valves (and float operation).

Some owners choose to eliminate the stock "S" hose between crankcase vent and airbox, and run a longer vent hose to exit underneath the bike*. However, this doesn't avoid gasoline into the crankcase via the combustion chamber, such as might happen where a petcock allowed fuel to flow (for whatever reason) while the bike is parked.

*



Good Fortune!

Thank you for all the information. It hadn't dawned on me that gas could get in through the airbox to the crank case. This is much rwlief as I have pulled the air box, and moved to pods. On my list of thinks to check are:
Clogged overflow tubes, and petcock vacuum hose leak.

I still have something that doesnt make sense..
Why am I leaking fuel in surges? Its not running out. Its water running into a bucket. It hits 4 ounces, then dumps, repeat. The floats appear to be moving freely, and there is no debris the float bowl.

Eddyv54 wrote: Thank you for all the information. It hadn't dawned on me that gas could get in through the airbox to the crank case. This is much rwlief as I have pulled the air box, and moved to pods. On my list of thinks to check are:
Clogged overflow tubes, and petcock vacuum hose leak.

I still have something that doesnt make sense..
Why am I leaking fuel in surges? Its not running out. Its water running into a bucket. It hits 4 ounces, then dumps, repeat. The floats appear to be moving freely, and there is no debris the float bowl.

Your 1st posting says you have a KZ650. Gas cannot get through the airbox into the crankcase on a KZ650. No way; no how. Even if you were to deliberately pour gas into the airbox it would run out through the drain in the bottom of the airbox before rising all the way up to where the breather tube enters the front of the box. Take another look at Patton's excellent diagrams. Ed

Same with the Z1 air box -- if you were to deliberately pour gas into the air box it would run out through the drain in the bottom of the air box before rising all the way up to where the breather tube enters.

Am thinking this is what happens with the Z1 air box:




The KZ650 air box design (with L shaped crankcase vent hose) would not have an open end facing upward inside the air box so as to invite something to run down into it.

Good Fortune!

Hopefully today I will have time to pull the carbs off and take pictures. I have no idea what would be wrong with the throat valve. It looks fine.......

Figured out why I had gas in the oil..

.. sort of made it stop spewing gas by tying one of the overflow tubes when a float got stuck..

Really bad idea that is. Good that you found it and one good thing comes outta this is that youll have a nice clean engine on the inside after this