Hi, well I have not been on here for a while and now am stumped. I have an old 16 hp Briggs and Stratton model 346431 model engine that is driving an old Simplicity tractor. After this winter I tried to start it after sitting in the shed for some months. It started immediately and I mowed with it for about two hours. put it back in the shed and tried to use it again and now it does not want to run. Drained all the fuel from the tank. Rebuilt the carb with soaking in carb cleaner etc. Set the high speed adjustment to 1 1/2 turns and the low speed to 1 turn. Put new fuel in the tank and tried to crank. It took some time and with choke on and the throttle stop on top of the carburetor pushed down it eventually would start. It took a while to run on its own but eventually started to back-fire at higher speed. It will not run on its own without some surging and running like it is runnung too rich. Readjusted the high speed and low speed screws and not much change.
I am now lost and so suspect the governor but not sure. Any help out there ?
Thanks.

just to be curious is this a cast iron block ? Check your flywheel key.

Hi, yes it is a cast iron block. I suspect that the "mices" built another nest right on top of the magneto and shortened it out and an initial backfire from that has sheared the key. I will find out once I pull the engine. Oh....I hate that. Thanks, take care and have fun

Thing is with those engines anything so much as moisture in the carb that causes even a little backfire will shear the key. Its such a heavy flywheel and a alumnium key

Hi and thanks for the response. Just this evening I pulled the engine and my neighbor is coming over to lift it on the bench. Will let you know what is going on after I have pulled the magneto cover and then the flywheel. Yes, the carb did have some moisture accumulation after it had run that this could be the initial reason for the backfire and it went downhill from there.
Well the neighbor just got here and the engine is sittin on the work bench.
So, I will let you know what happens. Sure hope the the key is aluminum and that it is the main problem. Thanks again, take care and have fun

I think the torq spec on that flywhell nut is 150 ft lbs

Hi philipmc, thanks for the encouragement! The engine is running again! Yes it was the flywheel key, it was offset by about 0.015". It is amzing how that small thing can create that much problem. In my case it is especially tough because I have to pull the engine as there is no room behind the cooling shroud. The mice had left the thing alone and the flywheel came off reasonably easy. There is a trick to putting it back together though as there is a type of universal that connects to the pump drive shaft. I assembled the front part of the universal but then when I tried to push the engine back the two bolts that hook to the drive shaft were pushed back some and slipped a bit into the universal fitting at the engine and cocking them. After a few tries I did find a thin piece of flat bar that slipped behind the bolt heads and held them perfectly. Oh, well live and learn. Thanks again for the help.

By chance does your engine still use points or is it eletronic ignition ?

Hi phillipmc, this engine is still using points. I think it is a weak point but found that is too old for the electronic ignition, I might be wrong but.........

Yes i was afraid of that, I tried putting electronic ignition on mine and it kept backfireing and shearing flywheel keys, even blew the head gasket once. It seems you have to send the flywheel off to briggs to get them to repolarize the magnet. Briggs will do it for free but you have to pay shipping to and from.