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1975 CB200T Mystery Leak

1169 Views 10 Replies 4 Participants Last post by  pattyandrick
I'm gonna start off by apologizing, because I'm completely new here, and to this bike, and I'm probably gonna sound like a big dumbass, but the other day I walked outside to an unusual smell.

Bike had been sitting unridden for close to a week, and there was now some new... residue under it, and a smell that I can only imagine is oil mixed with gas? The stain was fairly large, it didn't smell like straight up gas, and it wasn't reminiscent of pure oil (sure know what that looks like) and seeing as oil and gas are the only 2 fluids IN this bike, I figured it's gotta be a mix of the 2.

Oil's been slowly weeping from both crank cases since I bought the thing, so it's entirely possible that oil leaked on the ground first, and then gas leaked on top of it, but I moved the bike to a new location to monitor the leaking, and I haven't seen anything come out since (which is ALSO unusual...)

The gas level looks.. maybe slightly lower than the last time I checked, and the oil level looks... fine, and the bike still appears to run okay (for now). I don't see any obvious place where there's gas coming out, nor any new oil leaks.

Does anyone have ideas on where it might be coming from / things that would be easy-ish to investigate? I have a feeling at the very least new crank case gaskets are in my future, but if it continues to randomly leak gas on the ground, could that also be a head gasket issue?

I guess I'm worried that somewhere inside gas is getting in somewhere it shouldn't be, and then leaking out with the oil that normally comes out of the case, but it could also just be leaking out from any number of places (carbs don't appear to be leaking, but it's hard to tell which how quick gas evaporates).

Ideas for the most common causes of leaks on a cb200 would be super appreciated :X

Thanks so much for reading this far!
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"Assuming the carbs are okay, that essentially just leaves the pistons/cylinders right? Slight gap in the piston/cylinder interface would let unburned gas in the piston leak down the cylinder walls into the crankcase over time. "

No, any gas that gets into the cylinder will get by even the best set of rings. It will pass through the end gaps, even if the rings are perfectly sealed to the cylinder walls.
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