I have a Cub Cadet LT1018 with a Briggs 31Q777-0305E1. I ran across this thread while researching my problem, so I thought I would share my experience (and my stupidity) for others to learn. My fuel pump was leaking gas last summer, so I replaced it with the Briggs part. It started leaking gas again this fall, so this time I used an aftermarket part from Oregon. I installed the pump, and the engine started up just fine but then I started noticing white smoke. I shut the engine off and got a huge backfire (repeated this 2 more times and it backfired each time). I then parked it and let it run for 10 minutes but the white smoke started getting bad. I turned on the blades and a huge puff of white smoke came out. Then the motor died and wouldn't restart. I checked the oil and it was low. I then took off the carb and the carb was full of oil. I drained the oil and the oil smelled like gas. Based on the info from this web site, I assumed I had a blown head gasket, so I removed the head. I did have a blown head gasket, so I replaced it but the engine still wouldn't start. At first I assumed the carb was jacked up from all of the oil but then I decided to inject gas into the carb bowl...surprise, the engine ran for 10 seconds. Next step, pull the fuel line that runs from the pump to the carb and see if fuel is pumping...it was not. Fast forward a few days of thinking and I realized that I accidentally reversed the pulse and fuel input lines when replacing the pump. I was sucking oil from the crank and sending it straight into the carb. I switched the lines and everything works great now. Well, I also change the oil twice and the oil filter once. The only thing I couldn't figure out was: How was the engine even running with these lines reversed? All I can figure is this. Right before the fuel pump change, I topped off the gas tank to the very very top. I think that the gas was just running to the carb due to gravity. Once the tank got a little lower, the motor stopped because it had no gas. It had no gas because gravity could no longer feed the carb. In a way, this was a good thing because if the engine had kept running, I would have burned all oil and blown the motor.

I erroneously thought that some of the fuel pumps worked off pulsed compression, no reason they couldn't, but apparently all used on small gasoline engines operate off pulsed vacuum. Note: If it was a constant vacuum they would not work because the interruption in the vacuum is what makes it pump. From a B&S service manual we learn the following: "The fuel pump will prime at 30.5 cm (12") maximum lift. Fuel pump pressure is 0.1 kg cm/sq (1.5 psi). The pump is operated by pulsed crankcase vacuum." NOTE: "THE FUEL PUMP PRESSURE MUST NOT EXCEED 1.5 PSI." On this particular engine the pulsed vacuum line is connected to the valve cover.

Shucks, I accidentally hit submit . .................................................... Are you quite certain that the gas you are now discovering, was not already in the oil from before you undertook this rebuild? What may be damaged depends on how long the engine "ran" with contaminated and diluted oil. If the engine had been running with gas in the oil before the fuel pump work, I would expect the exhaust would have had a definite blue or blue-white color "smoke" in it. In which case, the most likely components to suffer damage would be the crankshaft rod journal and connecting rod, the piston and cylinder walls might have sustained some "scoring" or galling, but usually, the piston and cylinder of a 4 stroke engine, are "spared" in cases of gasoline contaminated oil in the crankcase. It usually requires that these engines be "run without any oil" before the piston and cylinder walls see damage (of course by that time, the crank and rod is usually "trashed" as well). Consider a 2 stroke engine escapes damage to the piston and cylinder with as little as 1 part oil to 50 parts gasoline. Also consider the the same amount of oil is sufficient to lube the crank main and rod journals in a 2 stroke engine, but ONLY DUE TO the 2 stroke design using ball or roller bearings in those 2 places. Plain bearings in the typical 4 stroke OPE engine will NOT survive long if run with diluted oil. If all the time this engine has actually run with gas in the oil, amounts to a mere 20 to 30 seconds, I believe all you have "suffered" is a solvent washing of the interior surfaces of the engine. Post engine numbers and let's see if we can find some illustrations of that carb. Maybe then we can retrace your steps during reassembly of the pump.

It vents the chamber so that the diaphragm can move freely. Proper service is to blow across the top of the screen to lift out oily residue if needed. Blowing directly into the port can damage the diaphragm.