Why will my 1977 arctic cat jag 340 run wide open great but trys to stall out if i let off?

after it stalls if i again hold it wide open and pull it over a few times it will run again (but only wide open)|||the idle/low speed jet inside the carburetor is plugged up|||fouled plugs is the most likely answer. could be clogged air filter clogged fuel jets but most likely fouled plugs.