Hi all - do I really need to 'oil' my air filter? I'm sure I never did that back in the 70s. It's a new foam one (Yambits). Silly question - what type of oil? (Yamalube 2-stroke oil? - I've got some of that). I'll spend 95% of my time on the bike on tarmac. I'm not after any extra performance. I'm just trying to set up my bike property for its first outing... Many thanks...

Hey,
You seem to already know the answer to your question.

Foam air filters are often designed to use oil as a part of the filtration process.
Leaving the oil out of the equation does sometimes give you an added bit of performance if you are in a race on a track. 
But at a cost, typically; you get more particulates into the engine, reducing the life of the engine.

If your air filter was designed to use oil, then this is what gives you good engine life. 

Some folks dip their air filter in a solution of 50% gasoline and 50% favorite filter oil, then shake out access.
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Dude
 

.....oh, as to your question of what oil to use, it really doesn't matter.  If you like to spend money, just google "air filter oil" and you'll get loads of companies wanting your cash.
However, you can use your 2 stroke oil, or just any motor oil.   Some folks use Bar and Chain oil for chainsaws cuz it has that "stickiness" factor.

Dude
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An unoiled foam filter is about as bad as no filter.  In a two stroke a little dust can take out the main and rod bearings as well as the piston and cylinder fairly quickly.

It's easy to over-oil the filter...  it doesn't take much.  Any oil is better than none.  Yamalube 2S will work okay.  

Most modern "sticky" air filter oils are terrible on these old bikes.  They restrict flow too much and cause running issues. One exception is Twin-Air Filter Oil...  easy to use, catches dirt like a magnet, and flows air great.

 

Thanks all - it's really great info.