Motorcycle Repair: gas in the oil problem, honda cb750k, second most common cause

Question
I have a 1976 Honda CB750k model bike and I have found that there is a strong gas smell when I checkedn the oil. I checked the floats on the carbs to see if they were hung but they were fine. I also changed the oil but when I drained it there was very little from the oil pan and the oil tank was full. I was just curious what may cause this.

Thanks ,  Duff Porter

Answer
Hi Duff,

The usual cause is varnished needle valves (float valves). The second most common cause is rust or other debris caught between the needle valve and needle valve seat.

When the needle spring varnishes, fuel may overfill the float bowl- no spring tension on the float tang. Same if needle valve cannot close seat.

Fuel would rise into the carburetor Venturi and flow into the airbox and cylinder. Once in the cylinder, fuel flows past piston rings and contaminates engine oil.

You may or may not notice evidence of defective floats, needle valves, or other carb parts.

Respectfully,
Mark Shively