i have a 400ex and all i have is a twin air air filter and an airbox lid with holes drilled in it. i rejetted the carb due to the modded lid. the stock main jet is a 148. i went up to a 150 and did not notice anything. i then went up to a 152 and did not notice anything. i was told to start high because you will know if it is rich because it will cut out on full throttle. well i thought it would be cutting out with the 152 in because all i have is three holes drilled in the lid. the plug looks the same with the jets. is there any way to tell if it is properly jetted? thanks

 

You are going about the right way just keep going up until it runs bad on top. You will know it then go down one. You should not have to move you needle but that would be next roll on the throttle if it stumbles drop a notch you will need to play going up or down methoticaly until it feels correct.
Next if it is hard to start or popps adjust your idle air screw if you have to go out more than 1 1/4 turns you need a different pilot jet.

 

i already have a 42 pilot jet in for easier starting, but it did not make it start better but thats alright. so you think i should go up to a 155 with just a modded lid?

 

Hey cals400EX,

While you're toying with the jetting, why not take your lid completely off? That plus the snorkel gone is one of the most helpful things you can do to a stock 400.

Do you know the RIGHT way to do a plug "chop"? The main jet should be simple, but tuning your carb for low/mid range is what takes finesse.

 

i am not sure what is the right way but here is what i did. i first rode the bike so it was warm. then i put in a new plug while i was on a country road. i then floored it for like 20 seconds pulled in the clutch and shut it off. i then checked the plug. this is how i did it, but not sure if it is right. the only thing i have a question about is where is the spot you look at on the plug for the reading. i was mainly looking at the tip. thanks