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My bike used to run just fine. Now it will only run about a minute then it stalls after dumping a lot of oil mixed with gas on the the ground out of the airbox. I have removed the airbox inlet scoop so I can see what's going on and this is what I see: an oil and gas mixture GUSHES out of the left carb into the airbox after the engine runs about a minute or less (won't idle on its own) then overflows onto the ground making a huge mess! I have no idea what's causing this, please help!

Stuck float on the left carb. Most probably the float needle valve has some gunk in it. It's likely just gasoline that gushes out. The crankcase breather vents into the airbox, so there's usually some oil in the bottom of the airbox.

I think you need to pull the left carb, crack it open and clean it out at the least, although installing a carb kit while you're in there wouldn't be a bad idea.

OK thanks, but I'm sure it's oil because it's red (Motul). I will take the carb apart after I order a carb kit from Amazon.

There probably are things you aren't telling us - how do you think oil can get into a carburetor?

Have you investigated those possibilities?

Well I have told all I know (which ain't much to be honest)! Oil that smells of gas gushes through the air filter from the left carb into the airbox then over flows onto the ground (I can't take this bike anywhere:). Its definitely oil because its red which matches the Motul brand that I'm using.

Maybe the engine is partially acting like a pump, pumping oil from the crankcase because the crankcase breather system is plugged up somewhere? That my guess, but I have already checked the breather hose and its clear, so maybe its further down range?

Like I said before the bike used to run just fine. It sat for a couple months then I started it and gush-gush all over the ground (splat).

Crankcases are often (usually? always?) vented to the intake manifolds so that some fresh air is drawn in someplace, usually on the clean side of the air filter, and drawn thru the engine and then burned along with fuel/air mixture. These are usually very small hoses. Backwards flow (how???) would only draw oil vapor thru those hoses when the engine is running and fully hot.

Clogged breather piping would have any crankcase overpressure going anywhere it could - possibly reverse flow. But it would only be vapor not oil/gas mix.

My money is on these possibilities:
(1) the bike laid on it's side for awhile (whether you know about it or not) and the crankcase oil seeped into places it doesn't belong. (explains oil but not gas) Should also show some external leakage though where depends on the motor and the side.

(2) Someone did a version of winter storage by vastly overfilling the cylinder(s) with motor oil which is being pushed back out the intake valve and carb when the engine is cranked. (that would explain the oil but not the gas)

(3) Someone did a version of winter storage by dumping motor oil into the gas tank and combined with a stuck float valve in that carb is now dumping from tank thru the carb to the airbox. (explains both oil and gas - stuck float alone does not explain the oil)

(4) You didn't say whether you were looking IN the airbox or just looking at the flow out of it (thru the filter?? thru the drain?) If it's gas flowing out of the air filter - do you have a K&N air filter? You know, the kind with the washable element that is oiled with RED OIL? (stuck float explains the gas, oil on the filter explains the oil but doesn't explain oil mixed with gas if oil is the dominant fluid)


Things to do - confirm that the crankcase oil level is correct (and not down by 1/2 qt)
- drain some of the gas from the tank into a clear glass container and look at it. Oily?
- pull the spark plugs and crank the engine. See if one or all cylinders blow out a bunch of oil from the plug holes.

General theme is that somebody has been messing with your bike.
Backup explanation is that your report of where the oil/gas is coming from is insufficiently in detailed. (possibility #4)

Thanks Ron for the reply.

I am the one storing the bike. No it hasn't been on it's side. I am looking inside the airbox when this happens. It does this
every time I start it (at least 5 times in a row now). The oil is full all the way. I have pulled the left side plug twice now, its a little dirty but not wet. The bike does not smoke when this happens.

Like I said, this bike may be possessed!

P.S. I keep it in a storage building (rent a unit type), So I can't see how someone is messing with it? But the thought has crossed my mind.

Definitely not a common symptom.

Disregarding the oil - you probably have a stuck open float valve (inlet valve).

One thing to try is opening the bowl drain for that carb to try flushing the obstruction thru. Might get lucky.
But ultimately you probably will have to drop the carb bowl and maybe remove the carb to get to whatever is holding the inlet valve open.

If this were my BMW I could tinker with the carbs without removing from the bike (and have had to) but you may not be as lucky.

I'm just really doubting the oil part of the story. Some crankcase vapor condensation - sure. But oil flooding??? You'll be able to tell US when you get it sorted.

Clean both carbs.

I plan to take apart and clean both carbs(soon), will let you all know the results.