400 ex rejet

[trxex]

well today i rejetted my bone stock 2001 400 ex.i put a 150 main jet and a 40 pilot jet. now i have a nice tan color on my plug.before it was light ,almost no color.it feels stromger in the mid to upper rpm range.the air screw i did not know if i should touch it .i turned it out 1/2 turn ,i guessed scince the pilot is now bigger it needs more air thats why i turned it out.sound right ??????

[Sparks425Ex]

What Reason did ya have for re jetting a bone stock 400Ex. The companys sends them out lean and that is how they are supposed to be. Unless you are very high above sea level you didn't need to re jet.

[jb400exxx]

he read in the manual that it says they come lean, and he wanted to fix it.

[jb400exxx]

i don't understand why but when mine was all stock i think it ran rich. the plugs kept getting all black, and it wouldn't start unless i cleaned the plug. since i got my pipe and filter and stuff and rejetted i have had no problems.

[northeast400]

mine ran perfect from the factory, but i have seen many people rejet an all stock ex and it ran much better. I work with new cars all day and I have seen the same thing with them. Same new cars but one runs better than the other.factory production lines don't do the best tuning.

[trxex]

true i re jetted because the manual said they were set lean,also my plug was white in color

I would think just by the plug test you did and the way Honda jets them stock that you are actually a little slower now.

Fact v/s Fiction

Fact- Honda sends all their quads out of the factory jetted (and just in general) rich for longevity. You wont be seizing up a motor thats jetted rich.

Fiction- increasing your jetting makes you faster and produces more hp.

Fact- too much fuel causing a rich condition will bog down your motor and rob hp, not to mention possibly foul plugs etc.

Fiction- a pipe mfg can tell you the right jetting to run on your quad

Fact- most times a exhaust mod will lean your overly rich stk set up just enough to run well.


I think you can get the idea from this. Jetting is not a simple bigger is better or thats waht they said to run project. You need to experiment with diffeerent size jets (and not just the main jet either) and will also need to change as the temp and altitude changes also.

Just dont get caught up with all the hype of the "know it alls" as many people do.

I still hear muscle car street racers braggin about the big ole cfm carbs they are running, but as allways you just laugh at this cause you know its way too much fuel for the motor they are running. Ever drive behind an old chevelle or camaro etc and see and smell all the unburned fuel and soot spewing out the tail pipe.

[trxex]

fact,honda jets lean from factory for epa ,emm reasons. fact ,the colder it gets the leaner the machine will run . fact,my plug was white (to lean) .fact,my plug now has a nice tan color.fact,a tad ritch is better than a tad lean.fact,i only asked for advice on pilot screw.fiction,your advice

[northeast400]

I thing the guy running 8's in the quarter is right. I also think the only reason Chevelles are spitting gas are to ruin all the little jap car wantabe racers behind them

:huh :confused: :huh

[Newbie400ex]

Seems to me it's better to be a tad rich than lean. Fuel cools piston etc.. If it ain't blowin' black smoke it's not too rich eh?

'81 mustang w/'69 302 0-60 5.1seconds

[0240099r1]

just to add my .02 worth my 400 has all stock parts some may have been messed with a little but i've got mine jetted to where most of you would swear that it can't be running good but i will bet that there's not another stock 400 that would beat it , there's prob. a few somewhere that would but most of you will get what i meant i think any 4 wheeler,car,bike that comes from a mass production has room for many improvements ........

[Yellow03honda]

I have a 2003 Yellow Honda 400ex i bought from sumone for 800 dollars well they said that the values was bent well come to find out they wasnt it was sticking on something well i got that fixed and when u start it up after you let it run awhile it has two headers coming out and one of them wants to get glowing red and i was wonderign what would cause that

[GPracer2500]

Originally posted by 440EX4me
....Fact- Honda sends all their quads out of the factory jetted (and just in general) rich for longevity. You wont be seizing up a motor thats jetted rich....

:confused: ummm, ok