Still have grandpa's 200 that he bought new in '55. Would like to get it running again and use the belly mount side mower on it. For the last couple years it would start and run with a miss for about 10-15 minutes and then start sputtering and die. It would then not start until you let it sit overnight. It also has historically had trouble fouling plugs if idled for very long. So I tried putting in hotter plugs and it still has the miss. The carburetor was all original so I sent that out to get rebuilt. Even with the new carburetor it still misses some and dies after running 10-15 minutes. When it does die if I pull the plug on the bottom of the carburetor it seems to still be full of fuel. Any ideas on what I can try? The fact that it runs for a few minutes and dies has me baffled. Thanks.