slower with mods? please help

[jsmith2232]

my 04' 400 ex ran 64.5 mph on the gps when it was bone stock - the spark arrestor, now i have an fmf powercore pipe, k&n air filter and jet kit, and a rev box, with the same conditions as i tested it stock i am now only getting 57.5 mph on the same gps,,, does any one know why or what i can do to fix this with out sacrificing too much low end...thank you

[2muchquad]

did you richen your main jet?your motor is beathing more easily so you need to add more fuel with the extra air your motor is getting.

[jsmith2232]

To be honest, i'm not sure because i had my honda dealer do it last week, i'll call them tomorrow and see what they did. thank you

[ghak99]

Improper jetting or an over oiled filter is probably the problem. Both are an easy fix and common mistake.

[jsmith2232]

does it sound like it needs to be jetted higher or lower?

[Dumontexrider]

Get a new spark plug, install it, and then run it full speed for about 2 mins. then quickly take out the plug. if its black its too rich, if it looks the color of pancake batter, its too lean.

[400exguy]

thats interseting cause my 99 400 with white bros. slip on and a K&N stock gearing with wore down stock tires ran 66 on GPS
e
then again I am a big boy.. so the weight might be the diff between adding some aftermarket parts and leaving it stock..on top speed comparisons

I just ordered some 22"s I will let you know how mush it sped it up.

[cals400ex]

make sure the throttle cable doesn't have more than a 1/4 inch of slack in it. this will greatly reduce the power output. find out what jet they put in the bike. did they put in a dynojet kit or did they use keihin jets?

[jsmith2232]

it was a dynojet kit, i contacted them today and they said they put in the recommended jet that the fmf powercore called out in the manual...is it possible that the jet needed may be different with k&n airfilters and a rev box? and they suggested to me that maybe it's the cold air or my rpm's are too high but those don't make any sense. also how do i see how much play is in the throttle cable.

[cals400ex]

push in the throttle lever and see how much slack is in there.



i dont know what fmf calls for. i would probably only run around a 155 with that setup. we need to remember that dynojets are numbered different that keihin jets too.