The fuel system on the bike is much like any other bike of the era, but it has vacuum operated petcocks or fuel taps. In order for the fuel to flow through, even with the taps in the on position, your engine must be creating a vacuum at the inlet side (Carburettor side) of the engine. See above. *Warning* The taps have no OFF position, they are either on, on reserve or prime. As you can imagine, as the bike gets older you get all sorts of problems with them, no fuel, too much fuel, fuel at the wrong time etc etc etc. The first symptom with mine was a smell of fuel in the garage as soon as I walked in. A small pool of fuel underneath the bike seemed like a small problem and easy to fix, until I read about gasoil, or fuel oil. This is when the fuel tap is passing fuel and the weight of the fuel in the tank overcame the carb shut off needles. (It filled over the top) When this happens, the fuel fills past the allowed level, and then straight into the pistons, past the piston rings and down into the oil. When the oil is thin then there's every chance that the engine will wear faster if not fail. I was lucky at this point. The only way to repair this is to replace the fuel taps with manual ones so that when the bike is left, the fuel is off. Another point to remember is that without the vacuum lines off fthe engine, the fuel may not/ should not flow at all. Common Symptoms of Fuel in the Oil Smell of petrol in the garage. Petrol dripping out of the airbox. Bike misfires and floods. Spark plugs wet but bike is not burning oil. Smell of petrol in the oil at the oil filler cap. 

Bike misfiring can also be caused by inlet air leaks. The air and fuel being mixed by the carbs must be well sealed from the atmosphere at the engine side or the bike pops through the carbs. In order to check these you must remove the carbs from the bike, and this can be a pig. Buy a Workshop manual. It'll help but what I doesn't tell you is that to get the carbs out you need to remove the airbox and to remove the airbox you need to remove the carbs. There are two ways to do this. One--The airboxes are often in two peices. Unscrew the screws that face the carbs and remove the carbs with the half airbox still attached. Two--Loosen the clips around the inlet rubbers, push them onto the engine, loosen the carb/airbox side, and push these rubbers inside the airbox, loosen the mounting screws to the airbox and drag the carbs out. When you inspect them, you'll find they have a habit of cracking, and ulitmately letting in air.  

 If you have just bought the bike, I would strongly recommend that you buy the carb overhaul kits and replace the float needles and jets. These do wear out. The choke seals also cause problems. If you don't mind that the bike isn't totally stock or concourse, then GET RID OF THE AIRBOX, because once you've had the carbs in and out a few times you'll want to bounce them down the street. Replace them with K&N style pods or make your own filter box.