Yes my grandfather said the diaphragm was shot in the carb. Not sure it it can be replaced or not. We still have the engine so if someone knows please chime in. The engine did run great for a short while and compared to my snapper 6.5 quantum it was a real fuel sipper. Used maybe a cup of gas to mow 1/2 acre. My snapper though will use a half gallon. Much heavier and self propelled pushing the ninja mulching blade. I did not concoct this story as I have nothing to gain from such a story. I am not representing or misrepresenting anyone. Just telling what happened to my mower which was barely used. I have a B&S 6.5 Quantum on my snapper that always starts and runs very good. I bought it used and believe it is about 7 years old. It has the ninja blade on it and bags fairly well as well as mulching. I paid $199 used for it 5 years ago as it was used for 2 years and owner wanted an upgrade. Some of the B&S engines are very good while their low end are not. I did mention in a previous post that I also have a tiller with the 16 HP B&S Vanguard engine that is incredible. So I am just stating their low end stuff is absolute junk. If some have good luck with them then great for them. So I am all for their great engines but their new low end stuff seems to be very poorly built.

I inherited a riding craftsman with an 18.5 doing the exact same thing. Gas in the Oil! This machine had only been used for one season, then put in storage for 3 years. When I 1st started it; it smoked horribly, and saturated the exhaust with oil. I've tried just about eveything, when a friend smelled gas on the oil dipstick. I drained the oil-and gas SHOT out . After putting in new oil-it fired instantly, and ran a few seconds, then shut down, and won't hit a lick! I've cleaned the carb, my 1st try at this, with no good luck. Guess I'll take your advice, and get a carb rebuild kit. What about the fuel coil? Do you suppose it needs replacing?

@walt2002, hey i was wondering if you were still here, i have read many of your replies and was hoping to hear from you and mownie, you 2 seem to have a wealth of knowledge on these things, i will try the carb first, because it is the easier than the head, but how would the carb cause fire to pop in the carb? im no genius but it seems compression is coming through the carb, and with the few parts in the carb, even no diaphragm, i cant under stand how it would be bad, do they have a ball and spring behind a welch plug like the old model walbro carbs?, i remember years ago when i worked on them a rule of thumb was if you shook them and heard no rattle they were no good, it had something to do with a barometric pressure adjuster valve, you didnt have to adjust the carb in higher locations as you did a b&s carb, just wondering, because i cleaned the carb twice, i put it in a bowl of water while disassembled and used a small straw to blow air through every hole, got bubbles on all, but i will swap them anyway and see, i just want to know what it is, thanks for your advice man

Kevin, the magnetos on these Briggs Opp Twins do have a dubious track record but my own personal experience with the one Opp Twin engine I own is a little different from what you are seeing. My engine runs well in hot weather.............until you cut it off and then try to restart it without allowing time for it to cool down. During the time the engine is still "heat soaked" no spark is delivered to the plugs. Give the engine a half hour to cool (or 10 minutes with a squirrel cage fan directed on the engine) and spark returns and engine runs. My theory on this is that so long as the engine fan is turning, the magneto is essentially one of the coolest components since it is located right next to the fan. In the case of my engine losing spark, I believe it is because the heat soaked engine mass radiates sufficient heat after turning the engine off that the magneto warms to the point that the electronic parts inside the mag fail to act properly and thereby don't allow a spark to be delivered to the plugs. I have not experienced any erratic spark or misfire so long as the engine is kept running. With those thoughts in mind, your slight skipping or flutter sound in the exhaust might be due to a lean burn condition caused by the fuel system design in conjunction with hotter operating temperatures (ambient air temp being just one factor). Lean burn or lean mixture means that the air to fuel ratio is "lean" regarding the volume of fuel present in the intake stream fed to the engine. Lean conditions can be caused by a few different things, some of which are basic design factors such as the size of the main fuel jets in the carburetor. Other factors that can result in a lean condition may be due to the "health" of the engine in general and how that health may affect the air/fuel ratio. One of those health issues is whether the fuel pump can adequately keep pace with the rate of fuel consumption. If for some reason a fuel pump can't maintain sufficient fuel volume to keep the carb bowl filled, a lean condition will develop. Since your fuel pump diaphragm has been replaced we must presume it is delivering enough fuel. Another factor that can cause a lean condition is the engine cooling system duct work that carries air from the fan to be directed over the cylinders and cylinder heads. If there is any kind of blockage anywhere in the air ducting sheet metal shrouding the engine.......air flow will be reduced across the hot surfaces and the surfaces will become even hotter, which will result in a lean condition. And because a lean condition actually burns hotter too, extreme air flow blockage will turn into a vicious cycle that might ultimately end in engine failure with catastrophic damage to cylinders, pistons and other parts. Somewhere below the extreme zone an engine can develop the "lean burn flutters". You would do well to remove all the sheet metal ducting from the engine and clean the cooling fins of the cylinders and cylinder heads. All too often we read in this forum where engines have been trashed because because mice built nests or food caches inside the cooling ducts and the engine succumbs to severe overheat without any forewarning to the owner. A word to the wise is "Clean your air ducts prior to the onset of the annual use cycle". Even if you don't have rodent activity there might be dust and mowing debris lodged in places that will tend to reduce cooling.