jetting help fast

[atvnut22]

my buddy is putting on a fmf powercore 4 slip on on his 2004 400, i need to know what main and pilot jet to use with and without the airbox lid. by the way, everything else is stock

[cjtrx400ex]

Originally posted by atvnut22
my buddy is putting on a fmf powercore 4 slip on on his 2004 400, i need to know what main and pilot jet to use with and without the airbox lid. by the way, everything else is stock


152 Keihin Main and 42 Pilot will get you in the ball park, you'll have to test it to get it right on, it all depends on your elevation where your at. I did a 155 keihin on my full Big Gun Evo-r exhaust but i'm stay in nashville it could be a +/- elevation where your at and it will effect you jetting. Keep in mind these are for Keihin Jets, if you by something like Dynojet or Mikuni you need to lot a this conversion table.

Even with this table you will still need to zero in on the correct jets, by checking the spark plug.

Width------Keihin # -- DynoJets # -- Mikuni #
0.0350---- 92.5--------- 92----------- 86.3
0.0360---- 95----------- 94----------- 88.1
0.0370---- 97.5--------- 96----------- 90.0
0.0380---- 100---------- 98----------- 91.9
0.0390---- 102.5------- 100---------- 93.8
0.0400---- 105--------- 102---------- 95.6
0.0410---- 107.5------- 104---------- 97.5
0.0420---- 110--------- 106---------- 99.4
0.0430---- 112.5------- 108--------- 101.3
0.0440---- 115--------- 110--------- 103.1
0.0450---- 117.5------- 112--------- 105.0
0.0460---- 120--------- 114--------- 106.9
0.0470---- 122.5------- 116--------- 108.8
0.0480---- 125--------- 118--------- 110.6
0.0490---- 127.5------- 120--------- 112.5
0.0500---- 130--------- 122--------- 114.4
0.0510---- 132.5------- 124--------- 116.3
0.0520---- 135--------- 126--------- 118.1
0.0530---- 137.5------- 128--------- 120.0
0.0540---- 140--------- 130--------- 121.9
0.0550---- 142.5------- 132--------- 123.8
0.0560---- 145--------- 134--------- 125.6
0.0570---- 147.5------- 136--------- 127.5
0.0580---- 150--------- 138--------- 129.4
0.0590---- 152.5------- 140--------- 131.3
0.0600---- 155--------- 142--------- 133.1
0.0610---- 157.5------- 144--------- 135.0
0.0620---- 160--------- 146--------- 136.9
0.0630---- 162.5------- 148--------- 138.8
0.0640---- 165--------- 150--------- 140.6
0.0650---- 167.5------- 152--------- 142.5
0.0660---- 170--------- 154--------- 144.4
0.0670---- 172.5------- 156--------- 146.3
0.0680---- 175--------- 158--------- 148.1
0.0690---- 177.5------- 160--------- 150.0
0.0700---- 180--------- 162--------- 151.9
0.0710---- 182.5------- 164--------- 153.8
0.0720---- 185--------- 166--------- 155.6
0.0730---- 187.5------- 168--------- 157.5
0.0740---- 190--------- 170--------- 159.4
0.0750---- 192.5------- 172--------- 161.3
0.0760---- 195--------- 174--------- 163.1
0.0770---- 197.5------- 176--------- 165.0
0.0780---- 200--------- 178--------- 166.9
0.0790---- 202.5------- 180--------- 168.8
0.0800---- 205--------- 182--------- 170.6
0.0810---- 207.5------- 184--------- 172.5
0.0820---- 210--------- 186--------- 174.4
0.0830---- 212.5------- 188--------- 176.3
0.0840---- 215--------- 190--------- 178.1
0.0850---- 217.5------- 192--------- 180.0
0.0860---- 220--------- 194--------- 181.9
0.0870---- 222.5------- 196--------- 183.7
0.0880---- 225--------- 198--------- 185.6
0.0890---- 227.5------- 200--------- 187.5

[Bridgewater]

^^X2

I would go ahead and buy a 155 main also for like what..3 bucks? just incase the 152 doesnt work move it up one and stick with the #42 pilot.
good luck

[rcatvrider]

It's hard to believe any of those conversion charts are accurate. The systems aren't interchangeable that they use for measuring. I have seen at least 5 charts with varying conversions. Your best bet is to go with genuine keihin jets.

[leasureryan]

I agree...stick to Kehin jets

Why is everyone with stock bike chooseing a 42 pilot? A 40 is just fine piped/filter/lid removed.

When I had an FMF PC4...I ran a 155K, 40 pilot. That was perfect jetting for my location, bike and mods. Jetting didn't need increased much, cuz the FMF just doesn't flow a TON of air. I hated that pipe, and sold it immediatly

But thats just my OPINION, it should get you in the "ball park", just my 2 cents, and don't listen to me

^^^(I have to say that or I'm wrong...hehelol)

[cjtrx400ex]

Originally posted by rcatvrider
It's hard to believe any of those conversion charts are accurate. The systems aren't interchangeable that they use for measuring. I have seen at least 5 charts with varying conversions. Your best bet is to go with genuine keihin jets.


I don't know about keihin to mikuni but dynojet conversion is pretty close because i've tried em, when the keihins weren't in stock. But when I got a chance to get the original keihins i got em so i do agree with that part that i would prefer keihin jets.

[cjtrx400ex]

Originally posted by leasureryan
I agree...stick to Kehin jets

Why is everyone with stock bike chooseing a 42 pilot? A 40 is just fine piped/filter/lid removed.

When I had an FMF PC4...I ran a 155K, 40 pilot. That was perfect jetting for my location, bike and mods. Jetting didn't need increased much, cuz the FMF just doesn't flow a TON of air. I hated that pipe, and sold it immediatly

But thats just my OPINION, it should get you in the "ball park", just my 2 cents, and don't listen to me

^^^(I have to say that or I'm wrong...hehelol)

Just like u said location location, i have a 40 in right now because that's what i use in the summer and now that its winter i need to switch back to 42 because its hard to start in the cold and with the 42 you can throw the choke away.