Managed to get out and use my 2010 290 today for the first time.

It was a bit slippery due to the cold and I was and bit (very) rusty, but all in all had a good day out.

Just something that did worry me a bit and that was the thick ish black oil that appears to be coming from the exhaust. It appears there is a small hole on the underside of the exhaust and its leaking onto the swinging arm. Also the exhaust pipe outlet is very black.

Is this just a two stroke thing ? running at 80:1 mix i-pone oil

Run it up n down the road for a few miles and it will burn the oil off. Most build up oil if not run hard or its a case of Caustic Soda and that clears out unused oil.

So you are adding 62.5ml(ish) to 5 litres of fuel?

Thats probably about as lean as you want to go in my opinion.

Your bike however, is giving signs of running over rich which seems odd, with such a lean mixture.

If it is leaking out of the bottom, it sounds like there is a hole that needs sealing. I reccomend you find someone handy with a TIG welder.

The Most concerning thing though, is that there is enough oil in your exhaust to drip out.

I run my 2011 290 at 75:1 (66/7ml to 5L fuel) and it doesnt build up with black at the outlet at all.

Have you 100% got your fuel mixture correct?

Run it up n down the road for a few miles and it will burn the oil off. Most build up oil if not run hard or its a case of Caustic Soda and that clears out unused oil.

I seriously recommend NOT using caustic soda. I did some experimenting on cleaning and re-packing some damaged silencers, and it does more damage than good in my opinion. Its ok in steel front pipes, but it eats through alloy like a hot knife through butter !

it was bitterly cold today, if your filter was a bit damp it may have frozen and caused the bike to run rich, it may have also suffered 'carb iceing' (this is usually coupled with poor runing) ( i have experienced both on my KTM).

We used to caustic soda pipes out a few years ago, but i havn't used on alloy, i would probably steer clear of this and run the bike up a road for a couple of miles, that should clear it out. wait till its a bit warmer though!