This is what I figured, but in a motorcycle group, someone was told that if the petcock wasn't closed, gas would go through the carb and get into the oil when the engine wasn't running. Why wouldn't the float valve be as good in a motorcycle as in a car or lawnmower?
Andy writes: It is. However , the float valve is a simple thing that is susceptible to a hair or piece of dust causing a slight leak.... In older motorcycles, like a Honda 160, cleaning the float valve was trivial. It is more complicated now, I think , because the carbs have a lot more pieces...
That being said, if the valve leaks JUST A LITTLE, the fix was to always turn off the stopcock under the fuel tank. That gets to be a habit after it floods the engine the first time. And a good habit.....
So, you need to get the float valve cleaned out, and then get into the habit of closing the stopcock in preparation for the time in the future when you go to start the engine and it is flooded. The problem doesn't usually happen when the engine is running because the fuel consumption is greater than the leak....
Andy in Eureka, Texas
It would, however in a car the gas is pumped from below so once the pressure is gone, no leak. A lawn mower is gravity feed (except those with a diaphragm pump built in), but usually just barely, the tank is seldom much above the carb. I motorcycle is the perfect storm; with the tank well above the carb and fairly large fuel lines.
OK. Makes sense. Thanks to you and andy.
The Honda CB450 that I posted about a few times in the summer and fall is running now, but not reliably or too well. I need to work on the throttle, which is hard to control. But it looks like it won't be until the spring. That's ok. It's too cold to ride anyhow.
I haven't had the problem with leaking gas afaik.
I've never flooded a motorcycle engine with gas for two reasons: shutoffs were easy to check and use, and carburetors were designed with floatbowl overflow tubes.
A neighbor ended up with the crankcase on his tiller full of gas because the shutoff was hidden and easy to forget. Another had it happen to his riding mower because there was no shutoff. I had a push mower whose tank would drain if left a few days. I never found gas in the oil but assumed the float valve didn't quite seal. There was no fuel shutoff, so I tried not to pour in more gas than I intended to use that day.
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