Fuel coming out of air box - Diagnosis

[Thierry]

Hello guys,

Was wondering if anyone could help me to diagnose this issue.

Last weekend I had a cool ride to a friend's place about 130 km away. The bike ran great, it was a wonderful day and a wonderful ride.

About 30 hours later, I get back on the bike to go back home and the bike runs really bad. I stop on the roadside to check it out and notice a strong fuel smell and some fuel dripping off the air box. So I smelled through the oil cap, didn't smell like fuel and oil color/level seemed fine so I made it home anyway to check this out at home.

I then checked my carbs because I've had fuel in my air box before due to a stuck carb float. So I suspected the same issue.. To my surprise, all floats were fine.. Petcock valves seem fine as well.. I inspected them according to Clymers' instructions.

I googled a bit and after a while, here is my theory:

I left my bike on the grass on the side stand for 30 hours, leaning in a strong angle because the stand was digging in the soft ground (my bad.. newbie here). I think that most fuel in the carbs must have run down in the left carb, making the fuel level very high. Then, I started the bike and left right away (without warming up) to avoid disturbing the neighbors and had to climb a very steep hill right away, which I did really slowly on 1st gear to warm up before hitting the main road. I think that during the steep climb, the excess of fuel in the left carb must have run back to the air box.

From then, the air filter was soaked with fuel, which would explain the bike running really bad, strong smell and fuel dripping from air box.

Does that make sense? What do you guys think?

Cheers

[motoman]

My first suspicion, would be a float is touching a bowl gasket. Float is either cocked a bit or most likely, when bowl gasket is tightened down gasket getting squished a tad is slightly hanging over to inside of float bowl. I suggest removing ALL float bowls and leaving gasket in place. Using a razor blade or X-acto knife, slice around inside of bowl removing any excess gasket material. Clearance for float itself is very minimal from sides of float bowl.

[motoman]

To add, I'd resolve that fuel overflow before riding bike again! That fuel hitting hot exhaust has caused more than one bike going up in flames here on the site!.

[Thierry]

Just had a look at those gaskets and there is close to 1/8" gap between them and the floats. I don't think this is the problem.

Also, if the gasket was the problem, I really don't get why would the bike run perfectly all the way to my friend's place, and would run terribly as soon as I left from there.

Something had to happen while the bike sat there. That's one of the reasons why I suspected the leaning angle..

[skids]

Just had a look at those gaskets and there is close to 1/8" gap between them and the floats. I don't think this is the problem.

Also, if the gasket was the problem, I really don't get why would the bike run perfectly all the way to my friend's place, and would run terribly as soon as I left from there.

Something had to happen while the bike sat there. That's one of the reasons why I suspected the leaning angle..

You say the petcock seems to be working OK. Did you put an open hose to it? With the spare fuel hose attached, you can suck on the vacuum line and fuel should flow (into a container) and stop immediately when the vacuum stops.

Other possibilities:

The pin in the float valve can stick in a depressed position, allowing a lot more fuel into the bowl. Don't check this unless you try flushing the valve first.

The pivot pin on the float goal posts can get corroded causing sticky floats. The fuel valve can get debris in there allowing leakage. Don't check this unless you try flushing the valve first.

You can flush it out (maybe) if you run the bike with the vacuum lines to the petcocks disconnected. Block the vacuum nipples at the heads by placing golf tees in the open ends of the vacuum hoses. Run the bike on choke to draw down the fuel levels. The engine will eventually become fuel starved and start cutting out. Then switch over to prime to flush fuel past the fuel valve needle seats.

[Thierry]

I did check the petcock valves like you said and everything worked as it should.

I just reassembled the bike and went for a ride as I couldn't find anything wrong. The bike ran just fine. So whatever the problem was, it seems like it was not permanent...

I'm still curious about what happened though..

[skids]

Just a hiccup. It happens.

[TopCatGr58]

Hey Thierry,

Your parked on the sidestand theory sounds close. The floats could have slid a little sideways on the float pin and THEN hung up against the case/gasket. Also, then running it low on fuel could have allowed the float to drop so far as to possibly catch the float needle and get it stuck sticking the float and needle valve OPEN so it then FLOODED. Eventually with enough fiddling with it, putting it upright, filling and draining, running it, etc., the float and needle seat could have worked loose and started working properly again.

Lesson learned, for more than a few hours parking...put on centerstand!

T.C.

[GUNNY1966]

I have similar issues with mine as well!

For starters:
1982 Yamaha XJ1100 Maxim
I bought this bike & have restored it from the ground up! I didn't rebuild the carbs however I did replace all the petcock seals ( kits ) & I also replaced the Diaphram ( kit ) & since it now leaks gas even with the petcocks turned in the OFF position! I have removed the air filter only to find it is flooding the air box. I've read the thread on carbs here within the forums: http://www.xs11.com/forum/forumdisplay.php?f=30
& I think I can solve this problem without taking it to the shop but as for the parts that I am concerned about.

If you have any suggestions as to what I can try feel free to reply!
Thank You :-)

[Thierry]

I would double check your work on the petcock valves. Then I would rebuild the carbs, give them a good clean and inspect all components you can.

There are tons of information on this website to help you do that. Also, Clymer has been a huge help for me.

[Bonz]

Yes, search function is your friend for a good start to information on any issue you can dream of, and even some you can't.

If it is coming out the airbox then it was a float/float needle/float seat o-ring in the carb bowls issue, no question. Petcocks may or may not be an issue as well depending on whether it stops at a nice puddle or you flood the driveway.

My SG did that on rare occasion and a tap-tap of the carb bowls with a screwdriver handle usually jiggles stuff back into position. Sounds like a one-time deal, like Skids said. More or less normal/expected if you own an XS long enough.

When I knew I had a problem was when it did it each time I shut the bike down and let it sit on the side stand then I knew something needed attention in the float/needle/needle seat o-ring combination. Usually one of the o-rings on one of the needle seats was the culprit.

[TopCatGr58]

For starters:
1982 Yamaha XJ1100 Maxim
I bought this bike & have restored it from the ground up! I didn't rebuild the carbs however I did replace all the petcock seals ( kits ) & I also replaced the Diaphram ( kit ) & since it now leaks gas even with the petcocks turned in the OFF position! I have removed the air filter only to find it is flooding the air box. I've read the thread on carbs here within the forums: http://www.xs11.com/forum/forumdisplay.php?f=30
& I think I can solve this problem without taking it to the shop but as for the parts that I am concerned about.

If you have any suggestions as to what I can try feel free to reply!
Thank You :-)

Hey there Gunny,

Just reviewed the manual for the XJ to refresh my memory. The carbs are essentially the same as the 80-81XS's, they use an O-ring under/around the base of the float needle seat, and viton rubber tipped float needles. You will want to get GENUINE MIKUNI carb parts/float needle/seat. The generic K&L ones are a different length and require a lot of float tang adjustment to get them to be set right. ALso, the float level is supposed to be set with the clear float bowl tube held against the carb body and plugged into the port on the bottom/side of the float bowl. However, the actual float height setting is about the same as the 81, at ~23mm NOT 25mm. If the carbs leak/flood then the float needle/seat is at fault. They should stop fuel flow no matter if the petcock is ON or OFF.

Once you get the carbs fixed, then address the petcocks. Did you take both apart at the same time and possibly mix up the handles....they are marked in the center outside with an R or L and are side specific. You say you replaced the diaphragm, I'm assuming you mean IN the octopus valve, that's the only thing with an actual diaphragm device. The petcocks just have the holy valve, the O-ring seal around the handle, and then the spring/washer against the outside of the handle to apply pressure against the petcock housing and rubber washer. The octy valve piston can stick, the spring can get compressed, etc..

T.C.

[GUNNY1966]

Reply!

I ordered the Petcock kits & rebuilt both of them as well as I re-sealed the sending unit in the freshly painted tank. I also rebuilt the diaphragm that controls the vac while I had it apart. Today I removed the carbs & it seemed the #2 carb was the soaker best I could tell but since I gott'em off I think it's best to go thru them all so as to avoid future problems. So with that being said, where is the best place to order all the necessary parts with a reasonable amount of $$$??
Before pic: https://gyazo.com/76efd56d241e65226cdb923661f9e0b8

After pic: https://gyazo.com/623e80fa9e262d028dec48730d93d9a5

Once the carbs are finished I'll upload some more pics!

[MPittma100]

Petcocks

Petcocks may be leaking, but not the cause of fuel in air box. Pull carbs off and rebuild all four. Before you reinstall them, put fuel to them off of the bike with a remote fuel source. Can even use the tank with longer fuel lines. Let them sit for several hours or days and check for leaks. You will want to use genuine Mikuni replacement parts ONLY for the rebuild.

[XJOK2PLAY]

Guys,
My '82 XJ1100 Maxim used to due this same thing...
Left on side stand, petcocks left on, overnight...
The next morning my airbox would be full of fuel, air filter soaked with gas.
Once, gas even went into the crankcase. It was just lucky I caught it before I started the bike, and changed the oil.

Leaky float valves are the usual culprit. Another thing that also contributes, is if the Octy has been removed. (Mine had been.) I learned to always turn my petcocks off when I'd park it overnight, and put it on the centerstand.
This solved the problem until I got a new set of floatvalves and replaced them.
Problem solved.

Those Maxim air filters are pretty much unobtainium anymore!
Don't wanna be fuel saturating those things!
Not to mention, an airbox full of fuel and one little backfire... lol...