Hello I have a 03 yz 125. It constantly foul plugs. I mix my gas at 40 to one. Asong as I'm on the pipe its ok. It sputters and crackled on the bottom end,but once you get on the pipe it rips. I have stock jets. Any help will be appreciated thank you crfn04

I recommend cleaning your carb most likely in the needle seat there is some dirt and is not letting the needle seat also if u perform this procedure yourself to use carb dip. using just carb spray does not work remove all adjustment screws and washers and dip the carb this will remove oxidation and road film from the carb also when dirt or oxidation build up occures this will cause the carb to deliver heavy amounts of fuel to the cylinders and at low rpm it basically drowns it which fouls the plug now remove the float and needle very important to remove the seat screw and clean when carb goes back together turn the air screw all way in back out one and a half turns install idle control screw all way in back out two and a half to three turns try starting the engine u might have to make a small adj to either one and listen for the engine to change rpm if it starts slowing or trying to dogg turn back opposite way till u hear a smooth idle starting that should help with the fouling problem

Smaller pilot jet