Ok, please don't flame me for this question. I have a completely stock 2004 400ex and want to improve it some. I am realistic, and don't need to be the fastest out there. I have seen "complete systems" advertised in magazines. Other than a pipe, what do I need? I have read about jetting and new filters...do I need this in addition to a pipe? What is the advantage of a slip-on vs. a full pipe? I am not too mechanically inclined, so you might have to explain it layman's terms.

I don't want anything particularly loud since I live in California. Price is an issue, so please don't direct me to something that costs $10,000 to purchase.

 

I will tell you what I did and the results. First if you change the exhaust without rejetting you will be lean and they are lean to start with. I went with the White Bros. "E" series slip on, a K&N with the precharger, and a 175 main jet with the air box lid removed. The results were very noticable especially in the low and mid range. I can stay in 3rd where I used to have to down-shift to 2nd. Total cost about $250.00. I have heard that the extra advantage of a full system on the 400ex is not that much more for almost twice the money. Spend the savings on a K&N and re-jetting. Honda's head pipe is very good stock. I went with the "E" series because you can add or delete disks to adjust for performance and decibel levels. I was a little leary at first of running without the airbox lid but it really made a difference and i run in sand and fine dirt mostly. Just try to avoid deep water and clean it after every outing. I think you would really like the results I know i do. Good luck and have fun.

 

What Quadzilla said! The stock head pipe is really all you need for a stock bore and/or stock compression motor. Putting on an aftermarket header with a stock motor might even take away a little power. I'd just go with a slip on with a K&N or a good foam filter (Uni, NoToil, White Bros) and remove the lid with an outerwears cover. I wouldn't buy a jet kit, just go to the dealer (or online) and buy the factory jets.

 

You will have to forgive me again, but what is the difference between factory jetting and a kit I purchase elsewhere? Is there a performance difference? Thanks for the replies.

 

Jet kits contain many different size jets and sometimes a different needle. They cost $40-$60 but you will only use one. You can just buy a Keihin (factory) jet for $4 apeice and not have to worry about what size it actually is (sometimes jets out of a kit differ in size compared to a factory jet) or so they say. For me its just a preference........................Keihin carb=Keihin jets

 

Ok, I get it. So I should just buy the jet size that is recommended by the exhaust manufacturer? Also, about removing the airbox lid. I live in the desert and it gets extremely dusty here. Will it hurt my engine to leave the airbox lid off?

 

I too don't like running with my airbox wide open. So, I use this- http://www.ehsracing.com/. There is an Outerwears that covers the opening. It catches the big stuff, and the filter gets the rest. Highly recommended!

I have run K&n's for years, but am now going back to foam, for an extra margin of protection. I prefer UNI (http://www.unifilter.com/). They have a metal basket insert inside, that is much less restrictive than the funky stock one.

As for pipes, I am partial to FMF. If you want a REALLY quiet pipe, get the Q. If you don't mind a little louder (but still under 96dB), get one of their other mufflers, but you will have to run a QUIET CORE. I have the PowerBomb header and PowerCore IV on the 400EX, the Ti-4 on the Z400, and the Factory 4 on the 450. Love them all, but the Ti-4 is the hardest to quiet down.

 

i got a u.m airbox and put the u.m lid on it same concept as outerwears over it

 

well i got a 44o bigbore kit and have a new cam in mine with a whitebros e series pipe and stock hearder pipe should i sell mine and save up for the whitebros promag or can i do somthin to the stock header pipe for more hp


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99 440ex
few mods

 

[quote]
Originally posted by: sandman99ex
well i got a 44o bigbore kit and have a new cam in mine with a whitebros e series pipe and stock hearder pipe should i sell mine and save up for the whitebros promag or can i do somthin to the stock header pipe for more hp


Get a larger header. My buddy put together a 416 with a stage 2 cam, 11:1, and port work but ran the stock head pipe, until someone told him to go bigger. So he got the FMF powerbomb (?) header and he said it made a big difference just changing the header.