I have a 00 400ex I just recently put a Pro-Circuit pipe on. I used a 155 main jet airbox-lid still on. Will this setup work ok I checked the plug after riding all day on this setup and it ran perfect. Also I tried removing the airbox to see how it affected the bike it seemed to run sluggish through the gears I am thinking maybe to much air. But when I put the lid back on and try it the bike does excellent. It has alot more power through the gears I am pleased with the pipe. But my main question is do I need to do anything else to the carb like raise or lower the clip on the needle. What do you guys think

 

You shouldn't have to change anything else. Just for kicks take your lid off and try a 172 main.
I am sure you will like the improvement.

 

Thank you for your help but in reply I have a few questions. One- Will this in anyway make harm the bike i would not think so in my opinion increasing the fuel to a 172main and removing the lid would wash out and be a good combo but that is just speculation. Two- Have you tried this combo and if so how much of a diff did it make
Three- If this is a good mod why is this the first time i have heard about it. Can you recommend any other good mods. Thanks

 

You need to check your jetting to see if you need the richen or lean out your mixture. Just by checking the plug after a day of riding with tell you nothing about the way that your machine is jetted on the top end. If the plug looks good when you check it after it has been idling for 10 seconds all that is telling you is that your pilot jet is right but you may be way lean on the top end a few seconds at one throttle postion will change the color of a plug.To check the main jet you need to put in a good clean plug warm up the machine take it out for a ride when you reach 3rd gear pin the throttle and ride it wide open for at leasts 300 yards and then shut it off before you even let off the gas, pull in the clutch and coast to a stop and them check the plug this will give you a correct main jet reading. I have a K&N filter FMF Power core 4 and a dyno jet jet kit on my wifes 400ex with the lid removed and had to go with a 180 main jet to get the main jet right on.

 

Myself and about 5 other guys were all running that setup with the K&N jet kit until 2 of us went to 440s. There is more difference than a pipe will give you. If you are worried about too much dirt,water and such getting into your filter quad61@att.net has a pretty good solution for it. For three dollars (jet) its the best bang for your buck. Apperently we have more time to spend trying to make our bikes run better and don't rely on others to come up with good ideas first.

 

Sounds good I will try that setup I have a Uni-Air Filter. So if i remove the airlid and change to a 172 this should increase performance and work well with the pipe. Have you ever changed anything other than the main. I thought the main was for half to wideopen throttle. If you no of any good links to sites with carb info that would be nice.

 

Do you have the jet kit? If so leave your other settings where they recommend and just change the main. Possibly up one on the pilot but we didn't see much difference.

 

I am confused now. I have a Pro-Circuit T-4 and i went with a 155 main. I didn't see much improvement over stock. With or without the lid it ran similiar. The guys at my local dealer are not much help. I brought my quad to a local guy who knows his stuff and he said the 155 was too big. My stock main was a 150, in the service manual it says the 400ex comes with a 148. I always thought that for each mod you should go up one size. Pipe, K&N filter=2 sizes. Why do the dyno jet kits recommend using a 170 or 165 for just a pipe, isn't this too rich? And plenty of people that post seem to have good results with large jet sizes. My local guy adjusted the needle position and changed the pilot and he put a 148 on, i only went up my brothers street but my throttle response is much better now. He told me if i get on it on high end and it coughs a little then go one size up. Yoshi and WB, they all say to go up one size from the stock for the pipe, so why do the dyno jet kits say to use such a big main?

 

I have a 2000 400EX and I had installed a K&N filter/Outerwear and MegaMax2.This is the jetting I went with having the lid on.158 main jet,it may be a little rich but I didn't have a 155 to try.It made a big difference.Check out GT Thunders website.Goodluck.