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1975 CB200T Mystery Leak

1171 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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Oof, my bad I'm also just realizing this is in the 250CC and up section, and it should be in smaller twins and I can't figure out how to delete it. My bad, my bad!
Whatever it is, I smell the same smell when I remove the dipstick, that I smelled when I first saw the stain on the ground. I think it's gas mixed with oil. :|

Now what?
Alright I got my sense together and am realizing the only ways fuel could get into the crankcase are through the carbs/inlets, or straight down the walls of the cylinder, which would really be more like a bore/piston ring problem than a gasket problem (right?)

I leave the petcock off when it's not being ridden, but it looks original and I've heard that they go bad pretty frequently. Gonna check out the petcock and pull the carbs off and check the floats. Wish me luck :X
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I'd advise that you create a new post in the proper section as the engines in the CB200 are different.
I attempted to, but it got held and then... deleted? by mods. I suppose I can re-post it now since it's been a few days, just kinda dumb, I can't figure out how to delete this thread so it's always gonna be a duplicate.

At any rate, I disconnected the fuel lines, watched the petcock for a while and shook it around a bit, didn't see any leaks. Put some tissue underneath the petcock as well and let it sit for a while, didn't see any evidence of dripping, but I CAN still replace it..

Pulled the carbs off and checked the floats. I think the float height was set a bit too high so I lowered it (like 2mm). No leaks in the floats. Put everything back together, changed the oil... crankcase still smells like gas. Carbs are super clean, and all the gaskets I saw looked to be in decent shape.

I don't exactly know how to confirm that the "needle seat" is correct other than the fact that when I re-assembled the carbs, I know the needle slide seated all the way, and everything is in the proper orientation.

Hard to tell at this point if it's residual fumes from the first leak or if it's still actively leaking. The oil level is still roughly what it was right after I changed it (I filled it to exactly the top line so it would be a little easier to tell if the level was going up) I'm leaving the oil fill cap off for a bit to see if the smell dissipates at all.

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.
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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.
Thanks for all the info! I believe the carb floats were initially set 2-3mm too high because whoever set them previously did it from the edge of the case (rather than the gasket mating surface with gasket removed) so I lowered them each about 2mm. I've been contemplating swapping the carbs out for replicas for a while- I might ultimately have to do that.

I'm mostly nervous that it's leaking because of the cylinder seals, and that ultimately the only thing that's gonna fix it is tearing down the top end and replacing the piston rings.
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