Another jetting question

[Rickyrebar]

I am getting ready to change the jets on my 400 and trying to get educated before I go out and buy a jet kit & have everything appart on the garage floor.
My questions are... everything I have read to date talks about changing the pilot jet and the main jet. I have read nothing about changing the "slow jet" does this need to be changed along with the pilot and the main? If so, do most kits come complete with everything needed to upgrade?
Which kit (brand) & jet sizes would be recomended?
I have a 2003 400ex / White Bros. slip on / K&N filter / 15 tooth front sprocket. Every thing else on the bike is bone stock.
I have read in past forums, other riders with similar set ups, going to a 40 pilot & 152 - 160 main (approx.). Is this close? How exact of a science is it?

[cals400ex]

Originally posted by Rickyrebar
I am getting ready to change the jets on my 400 and trying to get educated before I go out and buy a jet kit & have everything appart on the garage floor.
My questions are... everything I have read to date talks about changing the pilot jet and the main jet. I have read nothing about changing the "slow jet" does this need to be changed along with the pilot and the main? If so, do most kits come complete with everything needed to upgrade?
Which kit (brand) & jet sizes would be recomended?
I have a 2003 400ex / White Bros. slip on / K&N filter / 15 tooth front sprocket. Every thing else on the bike is bone stock.
I have read in past forums, other riders with similar set ups, going to a 40 pilot & 152 - 160 main (approx.). Is this close? How exact of a science is it?

what everyone refers as the pilot jet is actually the slow jet. the jet kits won't come with slow jets. they will come with a needle and some main jets.

personally i would just go buy individual keihin jets. it will be cheaper than buying the whole kit and is easier to tune in for most from what i read. what elevation you at and what temperature are you riding in? you running an air box lid? i wouldn't call it an exact science. some people run their bikes richer than others. this will help keep it cool but will hurt the power output of the bike.

[hondarider2006]

I'm not a jetting expert....and cals400ex could answer your question better, but I will tell you what I know.

When people are talking about there "Slow jets" they are talking about there pilot jet. Removing your choke and installing a 42 pilot(38 is stock) will make your starting MUCH easier. And no the jet kit does not come with this. If I were you....I wouldn't spend the money on a jet kit. I made that mistake, and I could have saved $40 by buying individual jets from the dealer. Give C&D racing a call and order you some jetting. I would say with your mods, which are the same as mine....shoot around a 155 main. Just remember to do a plug check after installing your jets:)

[hondarider2006]

Originally posted by cals400ex
what everyone refers as the pilot jet is actually the slow jet. the jet kits won't come with slow jets. they will come with a needle and some main jets.

personally i would just go buy individual keihin jets. it will be cheaper than buying the whole kit and is easier to tune in for most from what i read. what elevation you at and what temperature are you riding in? you running an air box lid? i wouldn't call it an exact science. some people run their bikes richer than others. this will help keep it cool but will hurt the power output of the bike.


And it looks like you beat me to it.....:p

[cals400ex]

Originally posted by hondarider2006
And it looks like you beat me to it.....:p


i guess i slipped it in before you got here. i am always on the ball. :D

[quadrider400]

FWIW.... the jet kits are not a total loss they come with a needle that is different than stock which does make a differance. If you have your choke out jet a 42 pilot (slow jet) as to the main jet there are lots of variables like intake, exhaust, lid on or off, piston and port and flow just to name a few .....:eek2:

[zephead400ex]

I would also agree that it would be more feasible (IMO) to buy individual Keihin jets. Buying the a jet kit will give you more jets, but you can only use 2 jets at a time:D My local stealership will allow me to trade in my old jets for new jets if they are still in good shape. But whatever works for you man.

I have my carb jetted at 42 pilot with a 152 main. I could go up to a 155 main and run just fine too, but my plug reads fine. I am at 1000ft w/ a temp about 70.

Rejetting is not hard, just time consuming.

Good luck.

[cals400ex]

Originally posted by zephead400ex
I would also agree that it would be more feasible (IMO) to buy individual Keihin jets. Buying the a jet kit will give you more jets, but you can only use 2 jets at a time:D My local stealership will allow me to trade in my old jets for new jets if they are still in good shape. But whatever works for you man.

I have my carb jetted at 42 pilot with a 152 main. I could go up to a 155 main and run just fine too, but my plug reads fine. I am at 1000ft w/ a temp about 70.

Rejetting is not hard, just time consuming.

Good luck.


yeah, i trade in my jets too at the dealer.

[zephead400ex]

Originally posted by cals400ex
yeah, i trade in my jets too at the dealer.

I am glad they are cool with that. Makes it a lot cheaper when trying to get dialed in correctly.

[cals400ex]

Originally posted by zephead400ex
I am glad they are cool with that. Makes it a lot cheaper when trying to get dialed in correctly.

i agree. some of the workers don't like the idea, so i just go to the ones that don't care. :D

[hondarider2006]

Originally posted by cals400ex
i agree. some of the workers don't like the idea, so i just go to the ones that don't care. :D


You guys are lucky....my dealer doesn't even carry jets. "yeah we will have to order them for you......" screw that....I think that is one of the reasons I went with te jet kit. When I want somthing....I want it now, and my dealership doesn't carry ANYTHING!!! Ahhhh the wonders of living in AK:rolleyes:

[tstrenuous10]

i was just talkin to hmf the other day and they said to run a 180 or 190 jet with their exhaust. im 1000ft and under and its 60-90 here. they didnt say anything about changing the pilot jet, just the main jet.

[hondarider2006]

Originally posted by tstrenuous10
i was just talkin to hmf the other day and they said to run a 180 or 190 jet with their exhaust. im 1000ft and under and its 60-90 here. they didnt say anything about changing the pilot jet, just the main jet.


that is WAY to large on the main. I would say somewhere between 152-160 and you should be fine. About the pilot jet.....It won't hurt anything if you leave it stock, just installing a 42 will make it easier to start. But remember if you change that than you will have to adjust your air-mixture screw. Usually around 2-2 1/2 turns out and it will be perfect.



Btw......Cal I beat you to it this time;)

[cals400ex]

Originally posted by hondarider2006
that is WAY to large on the main. I would say somewhere between 152-160 and you should be fine. About the pilot jet.....It won't hurt anything if you leave it stock, just installing a 42 will make it easier to start. But remember if you change that than you will have to adjust your air-mixture screw. Usually around 2-2 1/2 turns out and it will be perfect.



Btw......Cal I beat you to it this time;)


yeah, crap, i was doing some calc homework. i only have 2 weeks left (for this semester). i am getting excited.

[Rickyrebar]

Thanks all for your input!
This is what I settled for...
Bought a jet kit, used the supplied needle, 3rd slot down from top, as per instructions.
Installed a 40 pilot, 160 main with 31/2 turns on the air mixture screw.
Very impressed with the ease of starting, cold!!! As for how it rides? Have not had a chance to try it yet, though I will before the end of the weekend.
Can someone explain to me the "plug reading" trick?

[hondarider2006]

Doing a plug test is really easy...


What you need to do is take your bike out and ride it and get the engine warm. Then find somewhere that you can get it wide open. Ride it wide open through all the gears, and once your in 5th tapped out, pull in the clutch and shut off the motor. Hold in the clutch until you have come to a complete stop. Take out you plug and look at it. You are wanting it to be a tan type color. Around the color that cardboard is. If its white, you are to lean, and if you are black its to rich.

That test is for the main jet onlt. To test your needle, you need to ride around at 1/2 throttle, and do the same thing. And for the pilot jet, just let it sit there and idle. Hope this helps a little;)

[Rickyrebar]

OK, Sounds easy enough, I'll give it a try...would seem like I would need to use a new plug on each attempt, unless of course it is the perfect set up already.

[hondarider2006]

I just used the stock plug and it worked fine:)

[tstrenuous10]

quick question.......just installed a bill balance full system and started it up...backfired once and smells sweet when i turn it off. also i got white smoke comin out of it. is that cuz its new or just too lean?

motor is completly stock. this is the only mod i have. still have the orignal jets. gonna be going to the sto thursday so if yall could help me with the jets that would be AWESOME.



one other question off topic. that 40 and 42 main jet.....does it make your tank drain faster or is it no really that noticable?

[cals400ex]

i would try a 155 keihin main with a 40 or 42 pilot jet. yes, the pipes will smell and maybe even smoke for a bit when they are new.