Running too lean means, to much air not enough fuel. Telling by the spark plug only works if you test each individual jet, driving around the yard your using all the jets at random times so essentially you can't tell by just the plug. Were talking about the main jet being to lean which works at heavy throttle. Does it sputter and back fire after you let off at heavy throttle? Does the fuel smell rich?

 

You can only do a correct plug test after a w.o.t. run. Riding around the yard will not tell you anything.

 

yes treveiger, it does sputter and backfire. i'm glad you asked, now i feel like i'm getting somewhere with this. so now what? does this mean i'm running too lean, that i need to richen up the mixture?

 

Yep mine did the exact same thing so I put I 128 main jet an turned the mixture screw out 3 turns an It's a whole new quad, its more torquey and after a minute with choke on I can turn it off and it idles great and most importantly it doesn't back fire like that anymore. Ill probably bump it up to a 132 main this summer for mudding an see how it does.

 

Not only do you need to increase main jet size, but you may want to play with the needle clip setting as well as the air/fuel screw. The air fuel screw may be blocked off by a brass plug. If so, you will need to drill out the plug to get access to the screw.