Engine is a 2001 Merc 60HP Bigfoot 4-stroke with 4 carburetors. When laid up in October 2009 engine was running fine until several minutes prior to shutdown when engine started to stumble. In April 2010 I changed spark plugs and changed lube oil and oil filter and drained 4 quarts instead of 3 out of engine. Oil was brownish gray color. I suspect at least 25% of drained oil is gasoline. I checked compression of each cylinder and got 185 psig-195 psig. T'stat checked out OK - opened at 120F. Temp. Sensor checked out OK with OHM and hot water test. I changed t'stat and temp sensor anyway. Enricher checked out OK with 12VDC test. Opened fuel pump and diaphragms looked OK but I changed the inboard diaphragm with plunger anyway. Engine now starts and runs rough and stalls at idle. Fuel tank bulb will not stay hard. I changed bulb and fuel line but bulb still will not stay hard. I now suspect maybe a bad #1 carburetor float or needle/seat causing fuel to leak into oil. The #1 carb. is suspect because I find fuel staining on #1 new spark plug more than on other 3 new spark plugs. Primer bulb will get hard if I pump it fast but then it goes soft after a short time. This happens with engine running or not running. Is fuel being leaked off by one or more of the carbs? I really need to assure this problem is with a carb. because boat is in a cable lift and I have no trailer and I am reluctant to remove carbs while engine is over water. I'm using walkboards to access rear of pontoon boat and the engine.

Question is: Is there anything other than a carburetor float problem that would give me the symptoms of fuel in lube oil (making oil) and tank bulb not staying hard?