I have 3 2004 400ex's and 1 2005 400ex to hop-up a bit for the fam. I have come to the conclusion that I will be installing HMF pipes on them keeping the stock headpipe, K&N filter w/ adapter, rejetting, and one tooth down on the front sprocket. I know a lot of you peeps are familiar with this quad and have done these same mods and then some. Does all this sound like it'll make a significant power increase? What size main and pilot jetting would you run with these mods?

Thanks,
Frank

First thing I would do to a 400ex would be front shocks. The ride is much more enjoyable.

Suspension as Mike said would be best. Especially new arms and shocks.
Night and day difference and much safe/forgiving.

THIS MAY HELP

The pipe and filter will help as well but not tons.
Next bext motor mod is maybe a cam and or FCR carb.

I don't think I gained much by switching to a FCR carb.

Most defnitely do the pipe, air filter and rejet.

Step up from there would be a 416 kit. Pretty cheap if you look around. There is a guy in florida that sells the parts and does the cylinder bore for real cheap. I'll try to find his name.

Shocks are nice, but $$$$$

a good front end, axle and ZPS shocks will make you ride faster than most engine mods

I did a full Duncan system, K&N filter w/ adapter, rejetting. It helped a bit in the power department. I recently got new shocks and they made a improved the bike better than the other mods.

I went with Marvin Shaw coilovers. They are a huge improvement over stock shocks. For dunes use they are really nice.

PP

In conjuction with the pipe, jet kit, one tooth smaller front sprocket, I also put on a White Brothers High- Rev Kit which help a good deal.

Jeff

what kind of adapter do you add with the K&N? When you add the K&N plus the adapter, do you guys get rid of the air box and air duct?

How many rides do you guys put on one oil change? What type of filter/oil do you guys put in one?


Sorry, i am a banshee man, and just picked a 400EX up for my girlfriend...and i have tons of questions...



Kelly

I usually go about 25 hours of ride time between oil changes. It gets dirty quickly. If the motor is already broken in, I like to use Mobil 1 15w50 synthetic. (red top) I go to AutoZone or Kragen and get the STP oil filters...#SMO-15. They're like $4.00 or so a peice.

My 400ex is a 416 with a hotter cam, port/polish, Hi comp piston and NOW an HMF pipe. Runs REALLY strong. If I could drop a few pounds...she'd really fly. I also sprung for wider a arms, wider axle and shocks. It all makes a huge difference, but it is expensive.

SS

great info, keep 'em coming

Frank