Wiseco 440 Big Bore Jetting

[Redlinin]

My brother has a Honda 400 EX, just had it bored with a Wiseco 440 Big Bore kit, Big Gun Pipe and K&N air filter. The compression is 11:1 and he wants to know what jetting would give him the most out of this set up. He rides in Michigan only and temps range anywhere from 40 degrees to 90 degrees.
Any help would be greatly appreciated.

[Rdhanded2]

That is something you have to test out and see what works best for him. Each bike is different, and no one can say for sure what would be best. Call Big Gun, they could probably give you a good starting point. I know White Bros helped me out.

[cals400ex]

for a starting point with the air box lid on:

main: keihin 158
needle clip: 4th position from the top
pilot jet: 42
fuel screw: 2.75 turns out from lightly seated

[allaboutHP]

i have that kit in my 440 and the temps around here are similar, and it has a 170 main jet.

[Florida400EX]

Originally posted by cals400ex
for a starting point with the air box lid on:

main: keihin 158
needle clip: 4th position from the top
pilot jet: 42
fuel screw: 2.75 turns out from lightly seated

I run a 158 main and 42 pilot, with a stock motor, pro circuit full exhaust, filter, and no lid.... and it still has a little backfire. I'd figure with a 440 it would be way higher on the main.

[cals400ex]

everyone has their own opinion on jetting. i would never go with a 170 mainjet unless your motor was built to heck. that big just hurts your power too much. on my built motor, i would run this same setup as i told you. going from my stock motor to a higher compression 406 with an aggressive drop in cam, my jetting only changed 1 mainjet size. he is running the stock cam and a big gun exhaust, which won't flow the most. everyone has their own technique. i wouldn't go more than a 160 on the mainjet.


i bet your having backfiring problems on deceleration right?? if so, this is from your slow circuit. the fix for this is to richen up the fuel screw or pilot jet. however, with an open exhaust, it won't be uncommon to get a little cackle here and there even when the jetting is right.



sparks says to run a keihin 155 mainjet at sea level elevation, 80 degree temps, with an x-6 pipe (really high flowing), no air box lid, and a high flow filter. as you can see, the mods you have is less than these besides the piston. i would still run the 158, but good luck with your decision. :)

[Florida400EX]

Originally posted by cals400ex
everyone has their own opinion on jetting. i would never go with a 170 mainjet unless your motor was built to heck. that big just hurts your power too much. on my built motor, i would run this same setup as i told you. going from my stock motor to a higher compression 406 with an aggressive drop in cam, my jetting only changed 1 mainjet size. he is running the stock cam and a big gun exhaust, which won't flow the most. everyone has their own technique. i wouldn't go more than a 160 on the mainjet.


i bet your having backfiring problems on deceleration right?? if so, this is from your slow circuit. the fix for this is to richen up the fuel screw or pilot jet. however, with an open exhaust, it won't be uncommon to get a little cackle here and there even when the jetting is right.



sparks says to run a keihin 155 mainjet at sea level elevation, 80 degree temps, with an x-6 pipe (really high flowing), no air box lid, and a high flow filter. as you can see, the mods you have is less than these besides the piston. i would still run the 158, but good luck with your decision. :)

Yeah, I know the Pro-Circuit isn't the best exhaust, but it's a good one, and still has very little to keep air from flowing, if anything. Yes, I've messed with the air screw, and it still has a little backfire if you hold it WOT for a couple seconds. In Florida right now, the average day is between 90-100 degress.. maybe during the winter I'll drop to a 155. I think that a 155 would be pushing the line on where it would be too lean on my quad. Maybe some quads respond differently, cause none of them are exactly the same.

[cals400ex]

oh, if it is studdering at full throttle, your more than likely running too big of a mainjet. i don't consider the pro circuit to be a bad pipe.

also, as the temperature gets warmer, the air is less dense meaning you need a smaller mainjet. as the air gets colder, it will be more dense and thus you would need to increase the size of your jets.

[Redlinin]

ttt:D

[cals400ex]

you already have a lot of suggestions. ;)

[Redlinin]

So, always looking for more:devil:

[Florida400EX]

Originally posted by cals400ex
oh, if it is studdering at full throttle, your more than likely running too big of a mainjet. i don't consider the pro circuit to be a bad pipe.

also, as the temperature gets warmer, the air is less dense meaning you need a smaller mainjet. as the air gets colder, it will be more dense and thus you would need to increase the size of your jets. '

doesn't stutter, just once you let go of the throttle after a couple seconds of WOT, you can defeinetly hear a little backfireing going on. Nothing wrong with just a tiny backfire like I get, but once you hear loud pops, is when you gotta change.

[cals400ex]

if it backfires when you let off the gas completely, you could turn the fuel screw out a little bit. this should help out.