Yes it is the Pulsa jet with the gas tank on top of the carb. I checked the gas cap vent and it was clear. I was thinking it may be the pickup tube and/ or the jet with the mesh covering over it. I notice there was gas coming from the carb. I checked the connection to the manifold, gasket / diaphragm, etc. and didn't see anything. On the carb I see the gas was coming from behind a small round black ball. I believe the dip to is connected to it under the carb.

If it was me I would do complete fuel system clean up. Said this before with that many hours and years on it your fuel system is dirty and about to fail. I would Start at the tank. remove it, clean it out either by swabbing or pressure washing. rinse with gas or alky. Next I would replace all the fuel hoses, fuel filter, install shut off valve, replace the hoses after the fuel pump and the fuel pump vaccum hose. If you don't want to clean the carb. bowl and spray the main jet with carb. cleaner add some fuel system cleaner when you get it filled back up with fresh gas and clean system up to the carb. Also while I was in there I would also inspect the elect harness, switches, looking for loose hanging wires, chafed wires, rusty connections. plastic tie wrap any loose wiring that could get chafed or rubbed against moving parts. If you want it to last you need to do this very few years 6 is pressing it, but not bad depending on conditions you work your equipment in. I would also make sure I check the air filter often older vanguard are fussy with the small air filter between the cylinders. Now cylinders reminds me of cooling fins. have you checked them lately? Might want to revisit the owners manual on pre-ventive maintenance make sure you got all the bases covered. do that and that tractor may last life time???? another thing if you going by the 50 hour oil changes you better be mowing in dust free invoriment?? if not then 50 hours between oil changes is way too long hence extreme conditions in the owner maintenance schedule??

Did you use the correct filter? If you used a filter for an engine with a fuel pump and yours is gravity feed, that could at least "partially" explain the problem. Fuel simply doesn't flow fast enough. It shouldn't take till the next day to restart though. More like 1/2 hour? Unless you have a clogged vent AND the wrong filter. BTW, a "months old filter" could have become gummed up from gasoline deteriorating over the winter. This post was edited by bill_kapaun on Sun, Jul 28, 13 at 16:19

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.