Weird quick gas leak

[Mullineaux]

I had been on my xs11 in a few weeks and decided to take her for a spin today. I put the petcock on pri for 30sec or so and switched it back to On. When I started it gas leaked out the air box, less than a cup. I stopped the bike, let evaporate a little, started it again and same thing. Tried a third time, at which point the bike was warm enough I could take the choke off. No problems, not a drop. Went on a couple 5mi rides, no leaks when I stopped and nothing I could see or smell while riding. I did do the dipstick/lighter check and it doesn't seem like any gas got into the oil. Anyone else see this? I suppose if pri runs off the res plug on the petcock it could allow some gunk in the carbs and the gunk could have fallen to the bottom of the float bowl. In general I don't trust problems that fix themselves. On the other hand I don't have much in terms of bike futzing cash at the moment.

[3Phase]

Mullineaux,

If you have the '80G carburetors the rubber tip on one of the float needles could be dirty/bad, or one of the o-rings on the float needle seat assembly is bad.

Since you said it stopped leaking it's probably a bit of <something> on the float seat/needle that went through after the bike ran for a while.

Grab your handy-dandy fire extinguisher and with the bike outdoors (not on the front porch, under a parking structure or the big oak tree with a tire swing) tap on the float bowls a couple of times with a rubber mallet or a deadblow hammer, then drain the float bowls into a small clear container and look for water, rust, and dirt in the fuel. You'll know what to do when you see the fuel.

If the fuel is clean but it keeps leaking out of the airbox anyway, pull the carbs and clean the float bowls, needles and seats. While you have the float bowls off you should clean the enrichener jets in the float bowls and replace the o-rings on the seat assemblies too.

[DGXSER]

Turn the petcocks back to prime, I would also remove the lower air box and filter. Wait about 30-50 seconds and see if any gas come sout the back of the carbs. If nothing your good to go.

Most likely, the gas had evaporated from the bowls enough to let the float levels drop down and one or more got hung up. The vibrations from riding and such let it free up and work properly now.

When I sold Ruby to her new owner, we never went over the starting procedure completely (my mistake), so he did not know to turn on BOTH petcocks. He drained one side dry and it was missing and sputtering. After I filled him in on the need to open both petcocks, he said it also spit gas out the air box. I told him to tap the bowls with a screwdriver, cleared up and he has not had the issue again since.

[natemoen]

Just as a FYI, the dip stick lighter trick is a terrible way to check the oil for gas contamination. I did a test awhile back to see how much gas it would take for the oil to light. I don't remember the amounts but it was a significant amount of gas that had to be in the oil before I ever got a noticable ignition on the dipstick that I used. The amount of gas that would need to be in the oil was welll beyond the point at which it would cause significant damage to bearing surfaces in the engine.

So in conclusion: When in doubt, Change it out! A few quarts of oil and a filter is much cheaper than a new engine!

[GLoweVA]

Most likely, the gas had evaporated from the bowls enough to let the float levels drop down and one or more got hung up. The vibrations from riding and such let it free up and work properly now.

My theory exactly. Something VERY similar happened to me the other day.
I usually turn my petcocks off after I get home and 3 days later when I tried to start her and get ther to the gas station, it sputtered the entire time there, I thought it was due to very low fuel. I filled the tank and wouldn't you know it, gas out the air box. Tried tapping the carbs there at the gas station, no joy. I shut off the petcocks and limped it home.
The next day, I pulled the carbs, #4 float had hung up. It wasn't rotating very well on the float pin. I guess when the bowl emptied out (I found that the drain bolt was slightly not tight and the copper crush washer was toast.) that the float dropped too much and hung up.

So I guess that carb bowls like having fuel in them. Now I don't go more than 2 days before I open the petcocks and start her up.

[Mullineaux]

Thanks for all the replies so far. FWIW my petcocks don't have an "off" just res, pri, and on.

[Mullineaux]

Ugh! I was hoping to not have to do this. Where I am the motorcycle oil with zddp for the over head cams and without moly for the wet clutch runs close to $10/qt. Hopefully riding it for 20mi or so didn't screw anything up.

Just as a FYI, the dip stick lighter trick is a terrible way to check the oil for gas contamination. I did a test awhile back to see how much gas it would take for the oil to light. I don't remember the amounts but it was a significant amount of gas that had to be in the oil before I ever got a noticable ignition on the dipstick that I used. The amount of gas that would need to be in the oil was welll beyond the point at which it would cause significant damage to bearing surfaces in the engine.

So in conclusion: When in doubt, Change it out! A few quarts of oil and a filter is much cheaper than a new engine!

[Mullineaux]

Crap, I did some sniff checking on the crank case and compared it to gasoline, clean oil, and spent oil and I'm pretty certain I rode the bike 20-ish miles with gas in the oil.

[BA80]

Is the oil level raised? Over full?

[Mullineaux]

Is the oil level raised? Over full?

Hard for me to tell. When I did the last oil change I changed the filter too. I pretty much put in the 4.5L (if I recall correctly) and didn't check the sight window figuring it'll change when the filter fills up anyways. On the center stand now, the oil level is at the top of the window. But I don't really know what it was at before.

[BA80]

What I'm getting at is if the airbox had fuel in it that's the direction it flowed, away from the intake. From experience I can safely say that it won't flow both ways. It either flows into the engine or into the box not both.

My driveway is slightly uphill so if I do get leakage it naturally runs to the box. Also with the oversize tire I run on front it will do so on level ground also.

If your oil isn't over full I would say you haven't gotten any gas in there.

On another note. That $10 a quart oil your running is completely unnecessary. A gallon of Castrol 20w50 is about $14 at Wally World and works just fine.

[Mullineaux]

What I'm getting at is if the airbox had fuel in it that's the direction it flowed, away from the intake. From experience I can safely say that it won't flow both ways. It either flows into the engine or into the box not both.

My driveway is slightly uphill so if I do get leakage it naturally runs to the box. Also with the oversize tire I run on front it will do so on level ground also.

If your oil isn't over full I would say you haven't gotten any gas in there.

On another note. That $10 a quart oil your running is completely unnecessary. A gallon of Castrol 20w50 is about $14 at Wally World and works just fine.

My driveway is pretty level. Here's what my oil site looks like now:


I did notice the gas going into the airbox started running out the lower lip of the box for a little. I used 10w40 oil. IDK the crank case definitely smells "sharper" than either my left over 10w40 or last season's oil.

[BA80]

It looks OK to me but if it would give you peace of mind change it.

20w50 is what these engines call for and the Castrol GTX works just fine. Just be sure the API Service tag looks like this. The bottom of the circle being blank.