I have an 18 ohv craftsman lawn tractor. It would run 5 minutes and quit. Sometimes 1 minute and quit and sometimes longer and quit. I would wait a few seconds and it would start up right away (usually). I tried the vent cap thing, bought a new one. I bought a new coil, changed the spark, oil and oil filter, new air filter. Broke down and opened up the carb, no mess in there. So, I took the little black cap off the emergency shut-off solenoid valve (after a year of trying everything else) inside the carb, and guess what? It runs great. Frankly, I'm not stupid, so I really don't need this government inflicted nuisance.