What does it mean when...

[SpannerMonkey]

When you take your oil filler cap off after 5 mins of running and nothing but steam billows out of it, It's an air cooled engine on a bike that got vandalised. 4 stroke
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My bike? A YX140 powered one-off Monkey Bike, something a little different!

[Furrybiker]

Someone pee'd in your oil?

[Pete.]

There should be no steam, but there could be a lot of smoke.

Are you sure it was actually steam? For it to be steam there would have to be water in the engine. If that's the case you need to change the oil. There's an outside chance you might get some petrol vapour out if you had a problem with the fuel tap or carbs but you would have smelled that.

You might have got a lot of smoke out of there especially if the clutch was slipping.
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[SpannerMonkey]