First thing you GOTTA do is identify whether the smell is oil, antifreeze, gas, or something else. That is important to know, and could be unsafe. Very unsafe.

If your carbs are leaking fuel, they are leaking it on the HOT exhaust manifold, and could catch fire. That will also cause a smell.

If oil is leaking on the exhaust, (and it don't take much) it will also smell, and could catch fire.

If its antifreeze, you end up running out of antifreeze, and you overheat the motor which *probably* won't cause a fire, but maybe. ANd you could damage your engine.

Burning oil in the combustion chambers would smell, but go away soon after turnign the motor off. Thats a pretty safe sutuation, but costly to fix.

In any case, it would be best to figure it out as soon as possible, or have someone more experienced have a sniff.. My guess is that you've got a minor oil leak finding its way to the exhaust somewhere, but definitely get it looked into furthur. I've had all three of the above sutuations many many times.

-Matt