is it possible to change jets without taking the carb off? i am very curious because the shop manual i have says it should be done this way, but how can you tune the jets with it being off the quad?

 

I have not looked at the 400ex,
but the 300ex, the jet just unscrews from the bottom of the carb.


I would think it the same way(but im not possitive)

there should be a bolt on the bottom of the carb.......

 

You can change the main jet by just unscrewing the bottom of the float bowl and then taking out the main jet with a 6mm or 1/4 in socket. The pilot jet is a different story and the same with whanging the clip. The pilot you have to take the carb off, the clip the top of the carb only. The pilot should be ab out a 42 or 45 with the clip in the middle with a stock engine. Main should also be 152 or 155.

 

what kind of time am i looking at to change everything? and what kind of performance gains should i see with just the main jet vs. the whole deal

 

You do need to change the pilot to a bigger size so that it will start in cold weather. The first time that you change the pilot will take about 1 hour or more. The next time 1/2 hour. The main can be then changed also. If just changing the main, about 10 to 15 min. You will find that it will run much better and start much easier.