18hp Briggs & Stratton opposed twin- fuel problems

While I'm an avid do-it-yourselfer, this has me stumped. My 1992 Dynamark 18/43 riding mower, which was running fine 2 wks ago, is in need of aid. It's a B&S 18hp opposed twin cylinder (model 422707). Hard starting, then once it's running, it rev's up & down, wanting to stall. If you up the throttle from idle, it will only run if you pull the choke out about 1/2 -3/4. While this seems to me to indicate a lack of gas, meaning you have to run with the choke out to cut down on the air intake, this doesn't seem to be the problem. It's actually getting lots of gas. It sprays into the top of the carb like all heck. In spurts. Thus causing the enging to go from idle to high rpm as gas dumps in. BUT, as I said, close the choke most of the way, restricting the air intake, and it actually smoothes out and runs almost normal.
If any of you have any suggestions suitable for a DYIer to try, it would be greatly appreciated!!!! Thanks!

 

The gas you see spraying isn't an indicator... it will spray every time the engine lags and the governor kicks in. You have a clogged carburetor. Remove the top of the carb, remove the drain bolt on the side, clean the bowl, and through the drain bolt hole, you can see the main jet. It should be removable with a flathead or an allen wrench, depending on which yours was made to accept. If you can get it out, clean the hole well in the jet and the area behind the jet. This should get you going.

 

Did as you said and it started right up! Looks like someone had replaced the fuel line from the filter to the carb, with something not suited for gas. Turned the hose kinda soft and the gas picked up black rubber goo from inside the hose and ran it right into the port opening. Took some soaking to clean it out but all is well at the preaent time. THANKS again, South 40

 

Great! Glad to help, and thanks for the update!