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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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Do NOT run a cb200 with gas in the crankcase, even for a few minutes. You will absolutely ruin the cam shaft due to the different type of bearings used. You need to drain the oil and make sure no gas is left in there otherwise you are going to be looking at an engine rebuild in the near future.

You need to find out why the gas is leaking. Replacing that petcock is not that difficult or expensive. Also, check the floats, needle and needle seat to make sure nothing flows while the petcock is in the OFF position. I'd advise that you create a new post in the proper section as the engines in the CB200 are different.
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As long as the needle seat screws in and the washer under it remains flat and flush, it should be good and not leak. A float level set too high can still cause gas to leak through in small amounts even if the seat seams to be sealed properly. I had the same issue of gas in the oil (and overflow from the carb), and the float was indeed set a little too high (even though it was set to spec), so lowering it slightly fixed the problem for me. Be sure to set it properly, it's from the gasket mating surface (with gasket removed) and not the carb body lip.

Even if a small amount was allowed down the cylinder walls, it should be diluted enough to not foul the oil. I think you have an overflow issue from the carbs while the bike sits that needs to be fixed, aka a float level set a little too high possibly.

It's very tough to diagnose these problems as even the smallest thing can cause it. I spent nearly a year trying to fix this issue along with a host of other problems with mine. I ended up swapping carbs for Chinese replicas (brand name OEM/STD or OEMSTD or Wincycles) for $70 and my issues are fixed. Took a little modification and reuse of OEM carb parts but I am back in the game.
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