Main Jet

[SnowFlake]

At this point my main jet size is 175 and i have an aluminum air box with no lid and stock filter with an outerwear.I want to putt a twin air filter in and still ahve the outer wear on and try to amke some kind of lid on the air box to keep some mud and water out. when i do all of these changes will I ahve to change the jet size?
I really need help because iam horrible with jetting.

-snowflake

[ny300exrider]

yea you seem pretty rich as it is because i run a 175 with an hmf pipe and no lid and that is running close to rich as well. you will probably have to drop the main jet allitle for the loss in air due to the airbox lid being put back on

[SnowFlake]

But iam also moving from a stock air filter with an outerwear to twin air with an outer wear, idc that much if am a little rich anyways caue i dont wanna be really lean.


-snowflake

[SnowFlake]

I really need help on this:confused:

[haywire4130]

twinair should flow about the same as a stocker. if you want it to flow more, remove the flame arrestor mesh from the inside of the cage. if you run a modified lid, you may want to back down the main a couple sizes so you're somewhere between lid and no lid. trial and error (efi is coming!)

[SnowFlake]

Thanks alot i will prob get a 173 and 174 and see how that runs.

[cals400ex]

they don't make a 173 or a 174. if your only mod is the filter and air box, your way too big on jetting. do you have other mods done to the bike? what is the elevation your at? what is the temperature you ride in? i assume your running keihin jets?

[nicky slee]

Yeah! Whats the highest size of main jet you go up to on stock 400 carb anyway? I thought it was 170, but if im wrong please let me know cause this could be a good thing.

[SnowFlake]

at thsi point i ahve the stock air filter in with an outer wear and have an aluminum air box with no lid. I want to make a lid for my air box and put my twin airfilter in with an outer wear. I have the baffle out on my stock exhaust (dont know if that matters) and thats it. And i just wanted to know if i HAVE to change the jetting with these changes iam about to make.

Thanks alot,
Snowflake

[cals400ex]

with the lid on and twin air filter, i would put the stock mainjet back in. if anything, a 150 should be plenty.

[SnowFlake]

could i play with some kind of screw on the carb to make up for it.
And anybody else think a stock jet would work?

-snowflake

[cals400ex]

instead of buying a new pilot jet you could mess with the fuel skrew. the fuel skrew is a fine tune adjustment for the pilot jet. if you want to richen that up a bit i would turn it out 2.75-3 turns from lightly seated.

now, this will not affect your mainjet. if you wanted to be safe, you could just run the 150 keihin mainjet.

[SnowFlake]

Good idea ill get the main jet. what size is the main jet.

[400ex_drummer]

doesnt taking out your baffles burn out your piston rings?

[cals400ex]

the baffle shouldn't hurt the bike. if so, almost every aftermarket pipe would be hurting it more than the stock one with the baffle removed because many aftermarket ones are straight thru with less back pressure than the stock one even with the tip removed.

the stock mainjet is a 148 keihin
a 150 keihin should do you good.

[F-16Guy]

Originally posted by SnowFlake
Good idea ill get the main jet. what size is the main jet.
You need a 150 main and a 40 pilot (148 and 38 are stock size), both Kehin. A 175 is WAY big for your mods, no matter what the altitude or weather. You obviously know how to change a main jet, but the pilot jet is a little more involved. There is a "how to" article here:
http://www.exriders.com/techarticles/pilotjet.html
I know it says to use a 42 pilot, but I think a 40 works better in a stock bore/compression motor. This should give you easier starting, crisp throttle response, and a little better power overall. One more thing; make sure that the clip on the needle of the carb slide is in the stock position (second groove down from the top, I believe).

[SnowFlake]

Thanks alot that last post helped me out alot.

[cals400ex]

stock needle clip position is 3rd groove from the top, not the 2nd. the 3rd is right in the middle. everything else looks good

[kilabeez0]

wuts the difference between the 2nd and 3rd clip setting from the top?

[F-16Guy]

Originally posted by cals400ex
stock needle clip position is 3rd groove from the top, not the 2nd. the 3rd is right in the middle. everything else looks good
Thanks. I couldn't remember, the DJ needle has one less groove.

wuts the difference between the 2nd and 3rd clip setting from the top?
The needle position (adjusted by moving the e-clip up or down in the grooves) changes the mixture from just above idle to about 3/4 throttle; lowering the needle will lean the mixture, raising it will richen the mixture, relative to throttle position. A different tapered needle can also change when and how much the mixture changes, but most people stay with the stock needle unless you get into serious racing.
BTW, as far as the fuel screw goes, I would go about 2 1/2 turns out from lightly seated with a 40 pilot jet. That should get you close; you can turn it 1/4 or 1/2 turn either way to fine-tune if you need to.

[cals400ex]

Originally posted by F-16Guy
Thanks. I couldn't remember, the DJ needle has one less groove.

The needle position (adjusted by moving the e-clip up or down in the grooves) changes the mixture from just above idle to about 3/4 throttle; lowering the needle will lean the mixture, raising it will richen the mixture, relative to throttle position. A different tapered needle can also change when and how much the mixture changes, but most people stay with the stock needle unless you get into serious racing.
BTW, as far as the fuel screw goes, I would go about 2 1/2 turns out from lightly seated with a 40 pilot jet. That should get you close; you can turn it 1/4 or 1/2 turn either way to fine-tune if you need to.


i was thinking the dynojet needle actually had one more groove than the stock needle, but i don't remember...