Motorcycle Repair: Fuel shooting out air filter 1983 Yamaha, check oil level, crankcase breather hose

Question
1983 Yamaha 450 Maxim. This bike starts and runs fine, at least around the neighborhood, no smoke in exhaust.  But for some reason a LOT of gas (maybe some oil too -- not sure -- builds up in the air filter case, and spills out. After 10 minutes of riding, when I park it about 3 cups of liquid spills out of the air filter case and/or air box. When I remove the air filter and start the bike, it looks like a sprinkler shooting liquid out there. I'm wondering if the crankcase breather hose is clogged or something (I dont' even know what the breather hose does, I can just see it going into the air box), or if a drain hose is clogged, and why so much liquid is shooting around the air box. I'm a new rider, rookie mechanic. I've got a manual, I'd like to get it working to the point where I could ride it to the repair shop. Any advice is appreciated. Thanks, Dave

Answer
Hi D,

Look for a clogged airbox drain tube or drain plug. Remove it or whatever to allow the fluids to drain.

The problems could be an overfilled crankcase. Excessive amounts of engine oil will blow out of the crankcase via the breather vent tube (you described), and into the airbox. Check oil level.

A sticky float needle vale (fuel valve) will allow gas to flow past float, overfilling float bowl. Gas will flow up thru carb Venturi (main bore of carb) and into cylinders and airbox. If this is the case, change oil & filter and clean carburetors. New needle valves may be required.

Carb kits are available for between $15-25 per carb and include needle valves (and much more).

Respectfully,
Mark Shively