Oil Tank hole in center on airbox side?

Question for you guys,
on my 71 the oil tank has a hole in the center of the unit on the airbox side, was wondering what it is for? and would there be any implications for plugging it up?

basically i get quite a bit of oil coming out of it when warming the bike up.

thanks

Hi Paul,

I'm trying to understand the hole you're talking about. The oil tank on a '71 is mounts to the right hand side of the frame as opposed to the previous year that was the back side of the air box (central oil tank). If you mean the hole in the back air box plate that has a "J" steel tube, that is supposed to be connected by rubber hose to the oil tank breather at the oil cap area. If you over fill the oil tank you will get oil coming out here. Don't fill the oil tank higher than the low mark on the dip stick and don't fill the tank until after starting the engine and running long enough for the wet sumped oil to return to the tank.

Yep old oil tanks vented into tube on air box to suck into engine combustion, ok if mild mist but not so good for detonation and coke up if over filled blow out. In early-maybe all 750s if oil is showing on dip stick - its over filled. As mentioned oil drools pass pump into sump, some faster than others, so until you get a sense of how long yours can sit up, check there's enough oil in tank to run a few seconds until sump it pumped back to tank. Best it to let the oil just vent out cleaning up after until seems to stabilize then peer in tank or drain oil for sense of what's really Norton normal. Be warned to blip much with oil cap off but all of us should do it at least once. Most block off air box and run tank vent down under frame or onto chain to lube and mess automatically.