Fuel is "leaking" from my airbox

I bought this bike in pieces (1982 XJ650J) I got spark, finally with a used cdi box from ebay. I thought the petcock has a vent from the intake runner between the carb and the head that it connects to. However the first time the bike caught fire. I fixed the damage. Second time was last night I quit cranking on her when I noticed fuel coming from the air box. And the last time I disconnected the vent line turned the petcock to prime and she lit of briefly.

I believe I have a stuck float....

HELP!!! Im new to the carb'd bike any help would be great!

 

You do have a stuck float. I'm not ignoring your PM, just busy will respond as soon as I get a sec.

That's not a vent line; the small line from the petcock to the intake manifold is a vacuum line; it "signals" the petcock to supply fuel when the motor is running. "PRI" bypasses the vacuum-operated function and allows fuel flow all the time.

 

Yes a stuck or misadjusted float is most likely.

Yout petcock should have two lines. A large one going to the carbs for fuel and a small one from a vacuum nipple on an intake to the petcock. This allows fuel to only flow when the engine is running and the petcock in ON or RES. If everything works right.

 

Sorry, Im getting frustrated with my toy. I have seen it happen with old ford trucks that I work on. So I will pull the air box runners and see which carb has a stuck float then. Thanks guys.

 

Clean the carbs completely while you have them off if you haven't done so already or you'll be back here asking why it won't run right.

 

Yup, time to clean the carbs and check the floats. Also, check the crank case.....open the oil filler and take a sniff. If it smells like gas, you have a lot of fuel that has run down past the pistons and is filling up the crankcase with gas. This dilutes the oil as well as creates a dangerous situation. At best, you'll get overheating symptoms and at worst you'll have another fire. Neither of which you want.

As the crank case fills up, the gas/oil level can get high enough that it backs up through the crankcase vent tube and fills the airbox with fluid. That can cause a fire with a pretty good backfire.

If the gas doesn't leak down past the pistons, it can back-flow through an open valve into the carbs and flood the airbox, causing the same problems AND to make matters worse, I had one case where the gas back-flowed through an open valve and filled the collectorbox with gas. I was fortunate enough to be outside and happened to have a 5 gal bucket mostly full of rainwater within a few feet....otherwise that bike would have been toasted.

Long and short.........pull the carbs and clean them. Drain the oil and replace it along with a new filter. Doing that job may present you with another issue of a stuck oil filter housing bolt. That's not a problem job. Here's what you can do for that.....

If the head is rounded off....file new flats on it and try again

If it continues to round off, get a sacrificial socket and weld it on
OR (my favorite way)
get out your grinder and carefully grind the head away til the base of the "washer" part of the head is almost gone. Go slowly now, til the housing pops out due to the spring that is inside. Remove the housing, the spring, and the filter. Remove the rest of the bolt with a pair of vise grips and it will turn out pretty easily. Order a new bolt now, and you're good to go. IF you messed up the filter housing, those are available from people here on the site.

Keep us posted, we'll get you through it.

Dave F

 

Wow thanks dave! Lots of good stuff there.

 

If you take the trouble to remove the Header Pipes, ...

You can use a Pipe Wrench on the Shouldered Area just to the rear of the Hex Flats.

You can get a grip on that Shouldered Disk Area with a Medium or Small Pipe Wrench.
Use a length of Pipe to give you greater leverage on the Wrench.

Replace the Bolt.
Before reinstalling the New Bolt, ... apply AntiSeize Compound to the first 22mm of Threads on the Oil Filter Bolt.

(Alternatively, in the worst case. You can remove the Bulk of the Shouldered Area with an Angle Grinder and then grind-away the Inside Diameter until the Shouldered area falls-off.)