I recently put a Duncan Racing Double Barrel pipe on my 00 400ex. After installing the pipe I tried to run it just to see if the new jets were needed, of course it barely ran. I was afraid I was in over my head so I took it down to the local Honda dealer. At first they wanted me to remove my K&N and precharger and put the original filter back on(my first clue). I ended up leaving it there for a half day(I left them 3 different jets). When I returned they said it was fixed. They put on the K&N and precharger, however they said I didn't need to remove the lid, cut holes in the lid or go up in jetting. They said they adjusted the carb and it was running great. They couldn't believe the difference the pipe made.

I ran it all last weekend with the original jets. It was a lot faster!! It did backfire a couple of times and it had a faint pinging sound like the valves were tinging around(I think that might be the technical term ha ha). Overall it ran ok, maybe a little rough. I was wondering if I should change the main jet anyway? Would it make it run better? Would the carb need adjustment? I would appreciate any advice. Thanks

 

I think the first thing you should do is to do a plug read. You need to do a test run at at least 3/4 throttle..better yet, at full throttle for 1/2 mile. Cut the engine right there & pull your plug. If it is grey or even white you are running quite lean & risk expensive damage.In this event rejetting is necessary.
The rule of thumb in rejetting after adding a pipe is to go two sizes fatter on the main, re-test, & do another plug read. The addition of an after market filter makes this even more necessary. It's much safer to be slightly rich & drop a size than to go the opposite way. When your plug electrode is a tan or brown color you have the correct main jet.You should also use a new plug in testing to prevent mis-reading from prior coloration.

 

What color will it be if it is too rich? Will the carb need to be adjusted too? Thanks for the info. Any other ideas?
Dale y2k 400ex

 

if its rich, it'll have carbon on it..blackish color

if its either rich or lean you have to rejet the carb..its not hard, I wouldn't waste the money on having the dealer do it

 

I'm not sure what you mean, "will the carb have to be adjusted".If you mean the air screw adjustment, the nominal setting is one 1/2 to two turns out from seated. If you have an irregular idle then you can go 1/2 turn either way to correct it.That is the only adjustment, other than the idle adj that is possible on the outside of the carb.The jet needle inside the carb body is adjustable but it controls only 1/4 to 3/4 throttle and the nominal setting is in the center slot. If you have no problem in the above rpm range, I wouldn't even bother with it.

 

I have a related question, I just installed a new jet and K&N filter, do I need to change to the IDS2 exhaust or is my stock pipe ok?

 

nathen,
No, you don't have to add any pipe unless you want to for better engine breathing & performance. If you are satisfied with the way your machine is now, the only thing you might do is to do a plug read to check for a lean or rich condition due to the addition of your filter.