Oily situation

On a 72' CB750, how does one know the oil is getting into the engine. By filling up the oil tank, shouldn't gravity just do most of the work. I only ask this because when I went to pour in new oil in the tank the oil level won't go down.

Normally and I'm speaking of 2 stroke oil tanks like on my Yamaha RD there is a dearation vent with a hose that should let air go into the tank without firt entering....is your vent plugged?

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All of these old bikes have an oil pump, gear driven by the crank shaft (often located in the side covers near the clutch etc.). The tank on the 750 is just a convenient location to store the oil which is circulated in and out of the tank. There are two lines on the tank - one in, one out.

So the oil doesn't 'go down'. It should be at a consistent level in that tank.

Search CB750 PDF Manual and you'll find a downloadable Honda Service Manual on the site somewhere I think.