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Discussion Starter #1
Yeah it's not a TW but it's close enough. :cool:

Anyway, I had just filled the tank up to the max on my CRF and forgot to turn the tank to "OFF" When I went to start the bike in the morning it wouldn't start. I checked the tank and noticed it had drained all the way down to the reserve, so apparently the carb has a leak (Float problem?)

I figured no big deal, the TW I had did the same thing since I bought it but I put 13,000 miles on it without a problem. I'll just switch the tank to reserve and be on my way. Bike still didn't start. I then notice that there was no puddle underneath the bike. I checked the oil and sure enough the tank drained into the crankcase and mixed in with the oil. No wonder the bike didn't want to start. I did an oil change (It was at the 2,000 mile interval anyway, so no waste there) and have kept the tank off since.

Now what I want to know: Why in the world did this happen? Like I said I had the same exact problem with the TW - you'd lose the whole tank overnight if you didn't turn it off...but at least on the TW it drained out onto the ground. I can't see why (or even how) it could have drained into the crank case. Is there something seriously wrong with the engine or is it simply a carb issue? I was thinking maybe the carb overflow drain was hooked into the crankcase (God knows why it would be, though) and it wasn't.

Anybody have any idea?
 

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Your float stuck. The above is exactly what happened and why the petcock has an "off" position

Change your oil then fix your carb or it will happen again.

Oh, and take the door off your airbox, because it's full of gas/oil mixture now, as well.
 

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Your float stuck. The above is exactly what happened and why the petcock has an "off" position

Change your oil then fix your carb or it will happen again.
I would also check to see if there is a clogged or blocked carb overflow tube. The overflow is supposed to prevent this from happening, or at least give you a clue that there is a leak.

In addition to a stuck float, there may be a bad o-ring on the float valve seat which allows fuel to flow around the valve seat.





Overflow tube is sticking up above the float bowl rim.




jb
 

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Check your overfow and o-ring as JB has suggested.

Carbs will often bypass the overflow when the bike is on the kickstand and will send raw gas straight down the cylinder, past the rings and into the crankcase. If you try to start it in an overfilled condition the gas/oil mix will pump through the crankcase vent into the airbox, so make sure you check the airbox before you try to start it after fixing your carb problem. If your motor inhales a big gulp of incompressible liquid sloshing around in your airbo. you'll have far bigger problems,such as a bent rod.

I'm not familiar with your Honda's airbox layout but there is usually some sort of provision for draining the airbox in the event of a hanging float needle or failed water crossing.
 

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I would replace the float needle regardless of what it looks like. A bad one can look identical to one that works, and they are cheap! I had almost the same issue with an xr100 and a couple bucks for a new float needle solved the problem.
 

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Discussion Starter #7
I checked and cleaned out the air box, it's fine now. Bike runs great as it should.

Another question though - it's going to be a while before I have time to figure out how to properly fix the carb (my mechanical experience is pretty limited) Is the bike safe to ride as is if I keep the tank off, or can the oil end up being contaminated again even while the engine is running?
 

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As long as the petcock is "off" you should be fine.
 

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Discussion Starter #9
Thanks! I really appreciate the advice. Both my ex-TW and my CB250 have float problems where the tank will empty overnight if left on, yet it's never gone into the engine despite me wasting many gallons over the years putting 38k miles on the two bikes. I was thinking for sure that a seal or something inside the engine was ruined and I'd be looking at a major repair.
 
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