FMF Power Core 4

[Fruteless]

I just got a FMF Power Core 4 and put it on a 300ex. It is all stock. I changed the main jet to a 130 from a 122. This is what fmfm suggests. It is like 5 degrees here. When I started it up it shot flames out and it doesn't want to idle and there is hesitation in the throttle. Is fmf wrong or is it just too cold to run it out there. Does the pilot have to go up. I just cleaned the air filter with gas and bolted the exhaust on and changed the main to a 130. Can anyone help me out of my lost state. Thanks!:D

[JDiablo]

try puttin in a 42 pilot jet,when they give you those recomendations(sp)they do not no where you live,the weather,elevation,etc.So then how can they be correct with giving you the right size jets,that might be a range and then you wood probably have to work off of that,then maybe turn to air/fuel screw 1 1/2 to 2 1/2 turns out,im telling you that you will have to play around with it to get it were u need to be at

[Fruteless]

Thanks I will try that. Does the main sound like it is in a good range and how about the needle where should I change that to. Is there a trick to jetting without taking of all the plastic making a minor change and putting it all back together to test ride it.

[xc400ex]

First of all since its so cold out let the bike warm up good then see how it runs....yeah you will defintly need a larger pilot jet though because of the backfiring when letting off the throttle.

[JDiablo]

idk bout the main jet,idk were u live elavtion,and all that stuff,if it were me i wood go up some sizes,but if it is good and runs good then just leave it alone

[hondafox440]

What was the temperature that FMF stated when recommending a 130? You jet richer in higher altitudes and colder temperatures..

[RedEX Baron]

i just installed a megamax II on my 300, the FMF paper said to go up to a 130-135, the stock main that was in mine was a 130. if those are stock jets you are using..to small..i installed the dynojet stage 2 kit in mine..as per instructions..had a stumble off idle but just kept adjusting the mixture screw to get it right.. i also noticed if run with the airbox lid on in the cold it seems to run better..lil richer. on my airbox lid i made a sliding door that spins and exposes 2 -1 7/8 holes.. i can cheat on my adjustments with it..crack the openings to let just the right amount of air in.. i can also spin it shut to block out water if needed . i also live in PA

[Fruteless]

I think that the pilot does have to go up. Thanks for all the help. I am pretty sure that the flames were do to a fault of my own. I tried to start it up with the spark plug cap off and just dumped all of that fuel into the cylinder. I didn't backfire anymore. Where do I find the pilot jet.

[JDiablo]

you will have to go buy one from your local dealer,there isnt really a need for spending 50 dollars on jets and just have them sittin ther,jus buy a couple pilots like 42,45,ect.some main jets will not cost you more then 20 dollars for like 4 jets

[RedEX Baron]

i dont think you should have to mess with the pilot for your mods, just mess with the mixture screw, it probally just needs turned out a bit. i have the stock pilot in my 300 K@N airfilter with box mod, megamax II. and the Dynojet kit..had the hesitation till i turned out the mixture screw..

[cals400ex]

Originally posted by hondafox440
What was the temperature that FMF stated when recommending a 130? You jet richer in higher altitudes and colder temperatures..


the lower the altitude, the larger jet you use.


yes, you may be able to turn your fuel skrew out and not have to mess with the pilot. if the fuel skrew doesn't work for you, you will probally need to go one or two sizes larger on the pilot jet.

[hondafox440]

Originally posted by cals400ex
the lower the altitude, the larger jet you use.


D'oh, brain lapse. Thanks for catching that. Its LEANER in high altitude and warm air, and RICHER for cold air or low altitude.

[cals400ex]

Originally posted by hondafox440
D'oh, brain lapse. Thanks for catching that. Its LEANER in high altitude and warm air, and RICHER for cold air or low altitude.

no problem. ;)

i just want to clarify what you just said so others don't get confused. your bike needs to be jetted leaner in high altitude and warm air. this is because the jetting becomes richer at warmer temps and higher elevation.