Gas in oil

Seems I am getting gas in the oil somehow. Bike (85 xj700x) sits in the winter for 3-4 weeks at a time. The pee tube then drains a cup or so of a gas smelling like fluid. I noticed that the oil level was higher than in the summer as I usually keep it at the half way mark. I keep non ethanol gas in the winter and it starts right up. What would cause this?

 

I'm going to guess some combination of the petcock not functioning properly and at least one of your float valves in your carbs not sealing completely - so fuel a float bowl fills up and overflows through the intake, into a cylinder, and into the crankcase.

The petcock on the gas tank is supposed to stop fuel flow when there is no vacuum present. These can get leaky over time and need to be rebuilt. Or, if it was left in the "PRI" (prime) position, then of course fuel could have flowed freely.

The float valves are supposed to stop fuel flow when a certain amount of fuel is present in the float bowl of the carbs. These too can get worn out or dirty and allow fuel flow when they are not supposed to.

An internally leaking petcock by itself is usually not a huge deal - the float valves do their job and stop fuel flow. A leaky float valve by itself is usually not a huge deal - the petcock does its job and stops fuel flow when the bike is off. BUT, if you have both problems together, that's when fuel flow can get out of hand and you end up with it in your crankcase.

Anyhew, just my guess. Do you know anything about when the last time the petcock or carbs were serviced? Also, for the XJ700XN, you can still get shiny new OEM petcocks from Yamaha, so you don't have to mess around with rebuilding if you don't want to.

 

Makes sense what you say. I put a new OEM petcock on along with full carb service 2 years ago. Bike runs really good and this leaky condition only occurs when it is cold out. Bike sits in garage. I am going to do the carbs again with new shaft seals this spring. Just to be sure I will replace the float valves as well. Thanks.

 

An easy test is to just run some fuel line from the petcock to a container of some sort and see if fuel flows when it is not supposed to be - see if it starts filling up after an hour, day, etc.

 

Be sure to get the gas issue fixed, then change the oil before running the bike again.

Dan's explanation of the cause is likely spot on.