83 xj750R fuel leaking into the airbox when sitting.

Howdy folks, Just got my 2nd seca, first was an xs400 when i was 16. this one is an 83 xj750R seca i picked up for $550. runs great after fixing the ignition switch and doing basic maintenance ( oil, plugs and new battery)

anyways after filling up the tank with premium and carb cleaner last night. This morning I noticed my shop smells like gas, small wet spot on my floor under the air box drain tube. Took the top off it and the inside of the air box was wet with fuel. Now my question is, is this just a problem with the diaphragm on the valve off the fuel tank? or is it a carb issue?

on my 400 I remember I put a manual fuel shut off valve inline before the carb, but the lines on the 750 are tucked in there really good so I dont think that would be possible.

 

I would say that it's one or more of these symptoms. The carb needle valves are worn, the float height needs adjusting, or there is crap in the float bowls.
If the fuel is leaking past the tap diaphragm then the needle valves, if they are in good condition, will stop the fuel reaching the airbox by sealing the valve seat itself.
If ithe fuel is leaking past the tap, and the needle valve and seat are good, then the other thing to check is the float height, which could be allowing fuel into the airbox.
Also, the carb cleaner that you ran through the carbs could have dis-lodged some crap causing the overflow.
Try draining the float bowls first or just give them a tap with the end of a screwdriver or something. Don't whack them though.

 

You have one or more stuck or sticky floats.

A petcock issue will only "enable" the situation; so you could have a two-pronged issue. But the floats should shut flow off even if the petcock is on PRI.

Float issue for sure; petcock issue maybe.

 

okay thanks for the replies, ill try tapping the bowls first otherwise ill crimp off the fuel line until I have a chance to tear into the carbs.

 

Don't forget to check the crankcase for an "overfilled" condition, which is gas mixed with your oil - - more than say, a pint and your oil is no longer a safe lubricant.

(and rear brake check !! \/ )

 

Yes listen to them don't disregard the signs your bikes telling you. Your best to crap line like you said then pull the big line off to make sure gas wont make it in till you fix it. Also one thing I did just because is pull all 4 plugs ( one at a time or mark them)this will tell you what shape your carbs are in and how long this has been going on. Very wet plugs means its getting to much fuel all the time(needle or needle seat) non wet plugs mean its on leaking in well it sits.(floats stuck and is or is dirty so fuel keeps pouring in) That will give you an idea of how to go about your Carb fixing. How ever you go bout it there is help here on this site if you need it.. a. Carb rebuild gourmet and pets cock rebuild gourmet is here if needed. Yes a repair book is always good if you have it if not get it.

Trust me these last 2 guys that posted help me a good bit

But wish your luck



Don't forget brake line check to go with rear brake check nothing worse then a lock rear wheel and no front brakes to boot

 

Thanks for the extra info, my xs400 did that overflow thing which is why I put in the shut off valve. I noticed the fuel problem when I first brought the 750 home so I wasn't sure if it was an issue or just because the bike had to go on a road trip in the back of a truck. when I changed the oil there was no trace of fuel in the oil.

im gonna just end up rebuilding the carbs so I know ill have trouble free use in the future, I had a local Yamaha dealer as a sponsor back in the day so they are gonna sync up my carbs for me after I get them to safety it.

I already replaced the front brake lines and pads, and checked the rear brakes as well as replaced the gear oil at the final drive on the rear wheel.
the only thing left to do will be to find a replacement light bulb for the aux light.

 

As werid as this might sound if your dealer can't help you out free or cheap try Napa.. they seem to help me a lot with the bike even Len on here knows his parts and might be able to help (xjforever top right of page) just shooting it out there and welcome to the xJ family

 

So I drained then removed the tank, then disassembled, cleaned and reassembled the petcock valve, after re installing the tank and adding just over a liter of fuel, I removed the drain screws on all 4 carbs and left it on prime. going left to right 1-4, carb 1 and 3 started draining and flushed out some cruddy looking fuel for a while. I then tapped each bowl then put it back on prime and got #2 draining and even more crud out of 1 and 3.

nothing out of 4 so I pulled the bowl off and removed the jets, hosed everything down with WD-40 cleaned all the gunk out of the bowl and off the jets. then re installed everything. with the drain screws back in I put it on prime for a couple seconds then back to ON then hit the starter.
Fired right up and ran better than it has since I got it.
with that small amout of fuel in the tank ill check the air box tomorrow for fuel. then probably take the bowls and jets out of carbs 1-3 and hose them down too.

 

Cool. Now check your valve clearances.

 

So after adding a couple more liters of fuel and letting the bike sit for a day There is still no sign of fuel in the air box. tomorrow ill get it over half a tank, run it, then check it again after a few hours.

 

One, ... very simple way, ... to keep Fuel out of the Airbox and Crankcase is to install an Auxiliary Fuel Shut-off!

A Briggs & Stratton Fuel Valve does the trick. $10 - 12-Bucks.

Mount it right next to the Petc0ck.
Turning the Valve vertically shuts-off the flow of fuel.
Insurance against a Petc0ck that is leaking-by or deteriorating Float Valves.



After you install the Shut-off, ... "Paint" the Lever and the Hose Clamps with Black Nail Polish and the Valve virtually disappears.

 

I had to do something similar to my xs400 but I may do that yet just as added insurance for when the bike is sitting for long periods between use.