400es jet q's

[xtullyx16]

okay sorry about a jet/carb question but okay.. heres the info u need:

i have a 400ex

Engine mods- stock motor, hmf full system, k&n filter, stock carb

main jet- 155

pilot jet-38

needle- stock

okay soo the story- my original setup was fmf power core slip on with k'n and all that but i had a 150 main and 38 pilot and the needle in the stock position... anyways i got a hmf full system and hmf guidllines are 152 main and 42 pilot.. im wondering if anyone can give me a precise arrangements of main jets like 152, 154, 155 .. and as for my pilot does it really matter if its a 38 or 42.. i thought the 42 pilot was put in soo my 400ex would be easier to start and i could take my choke off.. but if i dont take my 38 pilot out will i lose some power??

thanks for all and any help!

uhm also anyone know a cheap place to buy jets??



p.s hmf factory is located 50 miles away from my house.. soo i dont think the jettin would be that diff.. since its soo close, and theres no hills in ohio!

[boosted3g]

put the 42 in and it will start easier and you wont loose any power. You will gain power and your engine will run cooler at idle and low engine speeds. The jets go 150 152.5 155 basically every 2.5

[xtullyx16]

okay... soo whats are some good ways to tell tht it is jetted properly??

i know like 2- spark plug reading ( does it have to be a new spark plug)

and when u downshift if it doenst pop and runs through the gears without falling on itself

[boosted3g]

I honestly dont trust a plug that much. If its covered in soot yes it is rich but you should already feel a power loss and know that. Do it all by feel. Keep going up on jet size until you feel the power start to fall off, then go back down a size. Honestly i would try the 155, it should be very close. Do the 42 and dial that in with the fuel screw. If its cold you might be able to leave it alone. If its warm lean it up some, or you can go with a 40. Either way it will run better with something larger than the 38. The pilot only really helps out at idle and very slight throttle.

[xtullyx16]

okay soo right now the temps are in the 20-upper 30's when i jettted it .. it ran fine but in the summer when its in the 80's will i need to rejet it?

[boosted3g]

you may need to drop a jet size in the summer, nothing drastic. I never really touch the jets too much once its dialed in. I just play with the fuel screw to help it start and it will fire right up in 10 degree weather just as good as 80 degree weather.