Small Engines (Lawn Mowers, etc.): Briggs V-Twin, electric fuel pump, briggs stratton

Question
Hiya,
Well, I just purchased a used 35hp Briggs & Stratton V-Twin offline. I have a hobby of making go-karts, and this is the biggest "small" engine I've ever seen. I believe that it is the biggest made by briggs...and I have already made a frame for it. I'm afraid that I can't supply you with a model number, as most of the cowling and the OHV valve covers had been removed when I got it. I asked the original owner for them, and he looked for them without any luck. I had to buy some second-hand, and they are made for a 24-hp engine, so they might not be much help. The engine is electric-start, but even after carefully cleaning all the fuel lines and the carb, and replacing the head crankcase gaskets, AND replacing the oil sensor and damaged cam and rods, this engine just won't start! It has spark, fuel and plenty of compression, but for some reason, it won't run. It tries, and will run rough for a few minutes, but then promptly shut down. I payed $500 for this engine, and will not give it up. There appears to be no mechanical damage anymore after the replacement parts, and the engine is well-balanced and when it does attempt an idle I can tell both cylinders are firing. Do you have any guesses? It's almost Christmas, and I was hoping to give this go-kart to my 14-year-old son, Andrew. He loves engineering and anything to do with engines and cars, and this would be his first motorized vehicle of his own. Please help me!
-Scott Johnson

Answer
Odd things like governor settings, choke and throttle settings.  Is the correct spark plugs in the engine?  Is there a fuel pump or are you trying to use gravity feed?  

If the engine will start but not keep running I always start with fuel systems.  Did the product the engine came off have an electric fuel pump or is it a pluses pump?  If a separate pump you will have to install one.  If a pluses pump is it operating properly.  

If none of these stick with fuel.  Remove the carburetor and take apart.  Remove the main nozzle and clean every air and fuel passages with a wire like one from a twist tie.  Blow out with carburetor cleaner or compressed air.  Be sure to get the passages that go to the small holes by the throttle plate.  If needed remove the welch plugs and clean.  Install new kit and mount with new mounting gaskets.  Attach throttle, choke and governor.  Check the intake manifold for damage and gasket damage. Replace them to be sure.  

If you get nowhere with this check valve push rods for damage.  Check valve clearance settings. and look on-line for a service manual for it.  Briggs uses the same size block for many different engine hp ranges.  The change hp by changing air, fuel and exhaust settings.  Hope this helps, let me know.