MTD mower starts but then pushes fuel/oil out air intake on carby
Got mower for free and had a go fixin, had been sittin ~ 2 yrs, sump full of fuel when I got it so I assumed needle/seat fouled and cleaned a little, drained sump, then tested operation by pushing float up with fuel in it. Sure enough fuel stopped and started with adjusting float level, so put it back together, fired it up and away she went!
It was very smoky but thought that was from sittin so long and let it run bout 20s, then, started to die down and all of a sudden oil and fuel starts sputtering out air filter intake and all over engine(had filter off to view inside for fuel leakage). So I'm a bit confused but came to conclusion musn't have gotten all fuel out of sump and it ignited from below and somehow pushed itself backwards??? So, oils down now and I top up oil, fire it up again - same S***!
BTW, what's the little switch for below the carby reservoir housing the float?
Extra info: MTD 155 1/C, 18 HP "Black Beauty" from Bunnings, 42" cut, Briggs eng 28q777, type 0624-01, code 960628zd, float had no holes, did valve clearances, new sparkplug, new oil (but when it pissed out new oil, I topped it up with 20W-40 car oil thinkin I would just get it running then drain it out later and put the SAE 30 in)
I'm no mechanic and would appreciate any and all help - thanks!
Anyone got a repair manual for one of these?