FMF Powercore 4 jetting

[HondaChris]

I forgot to ask in my last post....how close is FMF's jetting recommendations from their jetting guide? Its on a stock 400EX, with the air box lid still in place and fully intact, and is just the silencer. I have had a few tell me that they didnt have to re-jet at all for theirs with the same set-up. I was thinking about doing the jetting myself if needed, and having the local dealer check it after I'm done on their EGA, but this would be my first jetting project, and am a little leary of it. So any help/tips would be greatly appreciated!

Go up 1 size or maybe 2 on your main jet...:cool:

[TRFOXX]

With my powercore 4 slip on I went with a 152 main jet, and a 40 pilot jet. Needle at stock position, and it runs like a champ! No backfire, just runs really well.

[Texan32]

with the lid still on the box, 152 sounds pretty close

[TRFOXX]

lids still on but it has 6 uni vents in it also.

[gncc400exxx]

Chris sorry I havn't emailed ,it's been a little crazy here this past week.

I ran a 154 with a 40 and it ran great, but I only rode for a few hours with the pipe.

[Chanman420q]

i know this is old but what about without the lid? 154 mj and 40 pilot?

[MOFO]

Here's my jetting for the FMF Powercore 4....


40 Pilot (could go to a 42)
needle moved one clip
155 mainjet
6 airvents in my airbox.

runs like a champ....

[Chanman420q]

Originally posted by VWVR6
Here's my jetting for the FMF Powercore 4....


40 Pilot (could go to a 42)
needle moved one clip
155 mainjet
6 airvents in my airbox.

runs like a champ....

well ill run a 158......... and a 42 pilot, my gunna take my lid off.

How do i know if i need to raise a clip or not?? ive never done that before.....:confused:

If it is acting funny like cutting out from like barely any throttle to 3/4 its probably ur needle. U can try to adjust it with the air/fuel mixture screw too.

[Chanman420q]

i know how to adjust the air screw but what about the needle.?

The air/fuel screw is on the bottom of the carb u just take a flathead screw driver to get to it. Turn it out it makes it richer turn it in makes it leaner. If ur quad is acting funny in the lower throttle positions it is most likely your needle. Move the clip down (raises the needle = richer), Raise the clip (lower the needle) = leaner.)

[Chanman420q]

Originally posted by 93 300ex
The air/fuel screw is on the bottom of the carb u just take a flathead screw driver to get to it. Turn it out it makes it richer turn it in makes it leaner. If ur quad is acting funny in the lower throttle positions it is most likely your needle. Move the clip down (raises the needle = richer), Raise the clip (lower the needle) = leaner.)

ok so how do i do that

also ive got the jetting specs either a 152 or a 154 with a 40 pj but what with out the lid? 154 or 156?

[400extracc]

the best thing for u to get would be a manual....when u pull a part your carb u'll start to c what every one is talking about.

just a tip- don't loose the needle jet, it is the size of a needle.
re-jetting my carb, i droped it on the ground and took my 1 hour to find it and a bald spot on the left side of my head where i pulled my hair out

i think there is soming on the faq or just do a search.....

[cals400ex]

go to the faq and you will see how to move the clip on your needle. i don't know where your finding a 154 and a 156 mainjet at??? i would run a 152 with the lid in place and a 155 without the lid in the summer. in the winter, you may have to go up one size on the mainjet since the air is more dense.

ok take off the black top of your carb and the gold plate too. Take the little lock nut thingy off (this is under the black top by the throttle cable.) Go to the part that was covered by the gold top and unscrew the screw that is in the little bar runiing across the top. now take that bar off. Undo the two little screws by the needle. Now take that throttle slide out and take out the needle and readjust it. Then put it back together. Watch out some of those screws are really soft and can strip easy.

[Chanman420q]

ok heres the deal, i put the pipe on, took my air box lid off and rejetted with a 155MJ and a 40PJ. Its definitly rich, it pops, wont take off fast in the higher RPMs, like geez i was getting smoked by a stock 300ex almost :eek2: Now my question is, do i drop down to a 152MJ? or should i adjust the needle? i did a plug test and its black, not a wet, just black and the residue stuff rubs off a little.

[cals400ex]

i am confused. tell me all the mods you have. if you just have a full pipe and no lid, a 155 should not be way rich. i assume your using keihin jets, not dynojet? is your needle in the stock position? a 40 pilot should be fine. where is your fuel skrew at? some people have problems with the mainjet falling out which makes the bike run like crap. also, check all connections to make sure they are tight. such as: the boot that connects the carb to the head, all the connections that hold the carb on, and make sure the air filter is on tight. also, make sure your pipe is on snug to the head so no air is leaking. when you replace the header, you are suppose to replace the exhaust gaskets in the head. did you do this? also, what temp and altitude are you riding at? also, get a new plug and start over.

[Chanman420q]

UNI air filter (clean ) needle at stock possition, no air box lid, and a PC4 Slip on. Im using the stock header.

thanx to those who helped, i did a 155 MJ and it ran good ( yesterday before i posted here ) but when i went riding it sucked. Well this morning when i went to adjust the needle in hopes that it would help, it turns out my main jet fell out:p how does this happen??