This question is for people who have put on a pipe as their only mod. If I would put on a pipe on my 400ex, and only a pipe, would I have to change jetting? My dad and I are in an argument about this. I say that if I new pipe was put on by itself, jetting would need to be changed, but he thinks that it wouldn't.

 

I used to run a megamax ll on mine combined with a k and n filter and never had a jetting problem.

 

Depends what kind of flow you got.

 

I think you would want to. IF you are going to flow more air then i would assume you would want to flow more fuel. I just got the Pro Circuit T4 and i am going to put it on this week. I guess try the pipe and check your plug to see if you are getting the right mix. Other than that just change the main jet one size up for each mod. I am going with the pipe and a K&N filter so i am trying a 155 main jet. I'll let you know how it works out. Oh yeah, check out this link- http://www.off-road.com/atv/400ex/dg_pipe.html
They show you how to change the jets on the 400ex.

 

I had a white brothers pipe and K&N on my bike. It seemed to run ok but it was actually running very lean. You don't have to change the jetting but it'll run better if you do. It is a simple task, the stock jet is a 150 and you could go up to a 165 main with the airbox lid on or a 170 with the airbox lid off.

 

Fast453EX... are you using a 165 main with your 453? If so a 165 would be to fat for a stock bore 400. I know this depends on elevation. I'm at 700ft and every one around here that has a pipe and K&N mod only uses 152-155. I put a 152 on mine and it had a very good cinnamon color when I pulled the head off for the 440 mods. I also know that dynojet jet numbers are higher than Keihin jet numbers.

 

In order to settle the war with your dad, He is right! By just changing the tail, you aren't increasing the air intake unless you either change the filter or remove the lid. In order to gain your $200.00 worth, you need to spend another 30.00 and get the filter to let the engine pull in more air enabling your tail to release more exhaust. It can't make air on it's own. Maybe and only maybe you'll need to increase the main jet by no more than five numbers. The stock Honda main jet is a Keihen 148. Only a plug reading after the mods will tell the whole story on what your needs are. As someone else in the forums recently said, "if you could speak ENGINE, it would tell you what it wants."

My old pipe and filter needed no jetting changes..the plug was a perfect marshmellow brown using the stock 148. But recently I changed to the E-series full system and it required a 158 main and 45 pilot (all Keihen, not k&n). My elevation is 1200 feet and I ride up to 2000 with no need for change.

Your turn to buy the icecream!

 

I have a Pro Circuit slip on on my '01 400ex. I'm running a 160 main. The stock jet was way too lean.