xcr 400 cranckcase full of fuel

hello
I am writing for advice on my sled not running after having been running as if it were loaded up. It would not start, had spark, new plugs and good compression. The lower end plugs were removed from each side and quite a bit of uel came pouring out of each hole.

What is this a symptom of ruptured diaphram in the fuel pump or a stuck float?

 

Stuck float and/or leaking at the float valve. Fuel pump problems shouldn't cause that. Definitely change your oil now. Run the sled for a few minutes and change the oil again to get all the gas out of it. You would not only have gas in the cylinders, but in the oil as well.

Hope this helps,

Bob

 

I had the same trouble on an XCR600. Keep in mind that these engines are 2 stroke, which means that the crankcase fills with fuel/oil mixture, then compressed, and forced into the combustion chamber. This vacuum/compression cycle creates a vacuum signal at one or more vacuum ports which connects directly, or by a hose to the vacuum side of the fuel pump. This pulsing action makes the diaphragm move up and down, which pumps fuel from the tank to the carburetors. If this daphragm were to have a hole in it (which mine did), fuel will siphon itself from the tank, into the crankcase via the vacuum port. In a matter of time, the crankcase will be full of fuel. In my case, the engine seemed to be locked up, but it was just the volume of fuel in the crankcase that would not allow the engine to crank (liquids don't compress). You may not notice much trouble while the engine is running. To diagnose your fuel pump as the problem, you can remove it, and take the screws out that hold all of the plates together. There will be multiple gaskets, diaphragms, check balls, etc. in there, so be careful to note their location. Also, the gaskets, and diaphragms in the pump go in only one direction. If you get them flipped over, it may not work right. If you are unsure, I think the best thing to do is to spring for a whole new fuel pump, and avoid the aggrivation. Time is money too. I hope this helps you diagnose your trouble.