Fuel in the airbox, and thus, on my floor

[Dan]

Smelled it before I saw it. The airbox drain hose was leaking fuel, not just a few drops. There was also fuel coming from around the seam of the airbox. Pulled the stock air filter and there's gas in there for sure. Pretty drippy. Seems to be primarily on the left side, carb 1, but that may also be because the bike leans that way on the kickstand. It was puddled in the upper air chamber where the carb air intakes are. A few spoonfuls of gas and the filter was pretty wet with it.

Reading the forum, I figured petcock, which was new btw, but not OEM. Pulled the tank, put a hose on the petcock air line. On "ON" and "RES", no fuel comes out unless I apply slight vacuum to air inlet (with a hose I sucked on. Admit it. You've done it.) On "Pri" fuel flows. I never use Pri and am careful to not put park it with PRI on. This seems to be, I think(?) indicative that the petcock is working as it should.

Just to be sure I've put it on the workbench with a paper towel under it to watch overnight for any drips.

Question one: Could it be the case that the vacuum line is leaving some vacuum on there even though the engine is not running, thus releasing fuel?

Question two: What else would explain this behavior?

Thanks as always.

Dan

 

[Redman]

Q1: No cant think of anyway for vacuum to be trapped in the hose when engine not running.

Q2: Faulty petcock (if sure it was not left in PRIme).


Also, do you know to also suspect gas has flwed into cyclinder and then into engine crankcase oil?

 

[Guest]

Can you clarify: The bike is leaking fuel while it's just sitting there, and not running?

 

[Dan]

Q1: No cant think of anyway for vacuum to be trapped in the hose when engine not running.

Q2: Faulty petcock (if sure it was not left in PRIme).


Also, do you know to also suspect gas has flwed into cyclinder and then into engine crankcase oil?

Thanks Redman, so even though the petccock appears to be working as expected on my bench, it may still be bad? Is this common? I actually hope this is the case. I've never worked on carbs and don't care to pull them off again.

And I'll be changing the oil and filter, per your suggestion.

Thanks again

 

[Dan]

Can you clarify: The bike is leaking fuel while it's just sitting there, and not running?

Correct, it happens after a ride, when the bike is parked. Thanks

 

[Dan]

Update - left the tank with gas in it, with petcock on ON overnight on my bench, with no leaks.

 

[Steve]

Had the bike been sitting for a while before you noticed the leak? The seal in the petcock can shrink slightly with non-use.

I had a leak on my petcock the other day, too. Tank had been sitting on the frame over the winter with no hoses connected. I moved it to my bench so I could finish assembly on the engine. I noticed some gas on the bench top and made sure the lever had not been bumped to the PRIme position. It hadn't. I moved the lever to REServe and back to RUN and wiped the bench top. No more fuel drips detected. Not sure what started it, but simply moving the lever to another position and back seemed to cure it.

.

 

[2BRacing]

Correct, it happens after a ride, when the bike is parked. Thanks

Just a thought here - it could be possible that fuel is overflowing from the carbs into the airbox while the bike is running, and you would not be aware of it.

When the bike is parked, the accumulated fuel leaks out of the airbox.

Incorrect float heights and/or weak needle valves could be the cause.

 

[Dan]

Had the bike been sitting for a while before you noticed the leak? The seal in the petcock can shrink slightly with non-use.

I had a leak on my petcock the other day, too. Tank had been sitting on the frame over the winter with no hoses connected. I moved it to my bench so I could finish assembly on the engine. I noticed some gas on the bench top and made sure the lever had not been bumped to the PRIme position. It hadn't. I moved the lever to REServe and back to RUN and wiped the bench top. No more fuel drips detected. Not sure what started it, but simply moving the lever to another position and back seemed to cure it.

.

Thanks Steve, I was going to reach out to you directly anyway. The petcock is new, but not OEM. And no leaks in the ON position, off the bike, overnight. Bike had been ridden the day before. Gas showed up a couple of hours later. But I will say that I'd noticed the smell on other days also so I don't think it's the first time. Petcock seems really hard to move. I'm inclined to replace it as step one. Since you rebuilt the carbs, I would imagine a stuck / incorrect float height or needle valve would no seem likely.

 

[Dan]

Just a thought here - it could be possible that fuel is overflowing from the carbs into the airbox while the bike is running, and you would not be aware of it.

When the bike is parked, the accumulated fuel leaks out of the airbox.

Incorrect float heights and/or weak needle valves could be the cause.

Thanks, that could be the case, not sure how to tell. Bike runs good, albeit with a few backfires coasting downhill. Oil level in the site window is not rising, and carbs were recently rebuilt. I'm hoping it's the petcock, but it's new. I'll replace and see if it continues. Thanks again.

 

[Guest]

I’m betting you have a fuel valve going bad in a carb or two. That’s not a lot of gas and fuel can continue to flow for a very short time after the engine is stopped. If the floats and valves aren’t stopping the flow it gonna run into the engine or the airbox

 

[Dan]

I?m betting you have a fuel valve going bad in a carb or two. That?s not a lot of gas and fuel can continue to flow for a very short time after the engine is stopped. If the floats and valves aren?t stopping the flow it gonna run into the engine or the airbox

Thanks, new OEM petcock ordered. Will start there and move to the carbs if I still see it. Carbs were recently rebuilt so hope not.

 

[salty_monk]

Just a thought here - it could be possible that fuel is overflowing from the carbs into the airbox while the bike is running, and you would not be aware of it.

When the bike is parked, the accumulated fuel leaks out of the airbox.

Incorrect float heights and/or weak needle valves could be the cause.

This is exactly what was happening on my 1100G when I first put it back together. Because the filter is foam.. it can hold also a lot of fuel along with what's in the airbox which then gets released when you park the bike. Petcock was fine. New OEM float valves & seats cured it.

 

[Steve]

Petcock seems really hard to move. I'm inclined to replace it as step one. Since you rebuilt the carbs, I would imagine a stuck / incorrect float height or needle valve would no seem likely.

One thing you can do while waiting for your new petcock is to check the current one. :-k

Get two sections of hose that will reach from the petcock to the floor. Find two glass jars (jelly jars are good), run the two hoses to the two ports on the petcock into the two glass jars. Leave it overnight, see which jar has fuel in it. If the fuel port has dripped, you have a leaky o-ring in the petcock or a weak spring. If the vacuum port has leaked, you have a bad diaphragm.

.

 

[Dan]

This is exactly what was happening on my 1100G when I first put it back together. Because the filter is foam.. it can hold also a lot of fuel along with what's in the airbox which then gets released when you park the bike. Petcock was fine. New OEM float valves & seats cured it.

Thanks - that's the case here looks like. Foam filter was wet enough to wring out gas. Steve W did the carbs for me, so I have to suspect the petcock. Hoping so, since it's an easier fix. I've never opened a carb, but I can learn I suppose.

 

[Dan]

One thing you can do while waiting for your new petcock is to check the current one. :-k

Get two sections of hose that will reach from the petcock to the floor. Find two glass jars (jelly jars are good), run the two hoses to the two ports on the petcock into the two glass jars. Leave it overnight, see which jar has fuel in it. If the fuel port has dripped, you have a leaky o-ring in the petcock or a weak spring. If the vacuum port has leaked, you have a bad diaphragm.

.

Thanks Steve - I had already done this to test the petcock, sorta. I had the tank off the bike with fuel in it, on blocks over paper towels. I did not have hoses on the petcock, but it was set on ON, where it has been for 3 days now with no leaks.

 

[Gorminrider]

With a full tank? Knockoff petcocks can have weak springs holding the diaphragm plug in and gravity fuel pressure can push them out..OR the petcock can be intended for a bike with some kind of pump-regulator up the line....even so, your float needles should be holding the fuel back....

 

[Dan]

With a full tank? Knockoff petcocks can have weak springs holding the diaphragm plug in and gravity fuel pressure can push them out..OR the petcock can be intended for a bike with some kind of pump-regulator up the line....even so, your float needles should be holding the fuel back....

Actually - I had filled the tank recently. First I've heard of this line of thought. But the tank is still nearly full, has been on my bench for 3 days, petcock in, in the ON position, with no leaks. But I'm still hoping it's the petcock. Will swap out with the OEM petcock when it comes in. Thanks

 

[Gorminrider]

hmm.new petcock might help , if the one you have is sticking open when the bike is running but I'd still include the float needles and seats inspected, especially if it can't hold fuel back on prime the bike will run rich in normal operation if the float needles aren't working.
There's an O ring sealing seats so cross your fingers and hope this is it but otherwise if cleaning or a desperate attempt to burnish a scratch on the seat doesn't fix(fine valve grind compound), you need the whole kit.Previous owners (curse them!) have been known to scrape away with screw drivers in there attempting to...what-get the seat out?

 

[Dan]

hmm.new petcock might help , if the one you have is sticking open when the bike is running but I'd still include the float needles and seats inspected, especially if it can't hold fuel back on prime the bike will run rich in normal operation if the float needles aren't working.
There's an O ring sealing seats so cross your fingers and hope this is it but otherwise if cleaning or a desperate attempt to burnish a scratch on the seat doesn't fix(fine valve grind compound), you need the whole kit.Previous owners (curse them!) have been known to scrape away with screw drivers in there attempting to...what-get the seat out?

Thanks - hoping the new OEM petcock will help. The bike seems to be running great otherwise other than an occasional downhill backfire. Will post results.