i just bought a 2011 Yamaha big bear 400 4x4 for 2900 bucks it needs some work but I still think it's a good deal when I bought it 2 days ago it did not run good In 1st or 2cd or low RPMS it had a snorkel and a jerry rigged glass pack exaust brought it home removed the also jerry rigged snorkel pressure washed it rode it around and it seems like the problem reversed it runs ok until it hits 20 then it gets worse it tops out at 30 so I pulled the spark plug and it seems to be running lean the guy said he had the carb jetted and rebuilt after he put on the exaust and a snorkel he said it ran ok for awhile the it started again it only has 1250 miles he said it's only had the snorkel for 300 miles what should I start checking??



thanks !!!!

 

A rough idea if it is running weak is to pull the choke partly out when it starts to bog, if it runs better, fit a standard main jet/needle and see how you go with that.

 

I did I think it ran a little better but not much