Jetting

[400exr]

Well I finaly got my bike to run, so I took it out last night and rode it pretty hard. During the ride I noticed that at full throtle it would stumble like it was starving for fuel. So, I drag raced a 2003 stock 400, at the start my bike would get the hole shot by 2-3 bike lenghts and then around 4 gear full throtle he would walk away from me by 2-3 bike lenghts. We switched bikes and the same thing happend, the stock 400 would eat mine!, even though I have all the mods in my sig. Also the header pipe would glow after a few hard runs! I have a 165dj, 3 turns out on the air/fuel screw, needle on the 3rd clip, and stock pilot jet. Please tell me that if I make my bike richer that it will have more power than this!! :mad:

[cals400ex]

there are a few things to look at:
1st, make sure your throttle cable is adjusted properly. it should have less than 1/4 inch of play in it. i set mine between 1/8 and 1/4 of an inch. your throttle will not be opening all the way up if you have more play in the cable. this actually makes a really big difference.
2nd, i dont use dynojets. however, a 165 seems like a little much. i would go down a size or two and see how that works. actually, i bet your too rich in the first place. i bet if you make your bike leaner, you will have more power. if it was stumbling, your more than likely getting too much fuel. ;)
3rd, you are running aftermarket tires. i went one in wider in the front and rear on my 400ex and it drastically slowed me down in 4th and 5th. i guess it is because the aftermarket tires weigh a lot more than stock tires. i recently bought the stock size tires to put up front but i have not been able to ride the bike yet. i will see if it was only the extra weight or width of the front tires that slowed me down.
4th, what size rear tires you running? are you running stock gearing?
5th, when you installed your jet kit you didn't happen to more the needle jet holder did you? this is the piece that the mainjet skrews into and it has a locking nut on it to hold it in place. if this piece happned to move, it could be hurting your power. i find my bike to run the best when i can see 3 threads on the needle jet holder after tightening down the lock nut to hold it in place.

with this procedure, you should not be getting beat by your friend for any reason unless your parking brake is sticking or something is holding you back. let me know if you need more help.

[2004TRX450R]

Try turning the choke on. If it helps you are to lean. If it makes it worse you are to rich. Then adjust your main jet accordingly. It isn't abnormal for the pipe to glow especially at night you can see it a lot better. Personally I don't like Dynojet jets because the sizes are off form what the factory jets are. I'd say you should be running about a 152 or 155 stock style main jet.

[chad502ex]

Originally posted by 2004TRX450R
Try turning the choke on. If it helps you are to lean. If it makes it worse you are to rich. Then adjust your main jet accordingly. It isn't abnormal for the pipe to glow especially at night you can see it a lot better. Personally I don't like Dynojet jets because the sizes are off form what the factory jets are. I'd say you should be running about a 152 or 155 stock style main jet.

if your motor bobbles on top end (wide open and pegged for at least five seconds), then the motor is too rich.

Yes, you can loose a race if your too rich, the motor bobbles and looses power!!

try reading my "Carb Chart" to help you dial your quad in,..

http://mywebpages.comcast.net/chad502ex/carbchart.htm

hope this helps you.

chad502ex.com

[2001400ex]

Listen to cal...he is a genius I tell you!:D

[2004TRX450R]

If it is to lean it can also spit and sputter. It will do it differently but it will do it. You have to be able to tell the two apart and if you are asking on this forum about jetting you probably can't tell the two apart. So do a more air/less air test like I said and first turn the choke on. That will give less air and will let you know which way you need to go. It would in this case apear that he is lean due to the main jet size but that is just a very easy test to get you going in the right direction.

[cals400ex]

if you are worried about your headers glowing, you need to see if they glow at idle, 1/8 to 3/4, or full throttle. and yes, i am a genius. :D just kidding. i learned from the pictures on this site and doing the trial and error method. i have tinkered with my carb so many times i am sick of looking at it.

[2001400ex]

Originally posted by cals400ex
i have tinkered with my carb so many times i am sick of looking at it.

LOL me too...mine is sitting in the garage all torn apart and I'm not even going to look at it until I feel like it.:D

[chad502ex]

I would not suggest to my worst enemy to run wide open running a lean condition... we all should realize the result of running wide open running lean, right? can you say piston melt-down?

It's ok to run as lean as you want down low RPM, but lean on top end even on 4stroke will cause failure.

chad502ex.com

[2004TRX450R]

Originally posted by chad502ex
It's ok to run as lean as you want down low RPM, but lean on top end even on 4stroke will cause failure.

chad502ex.com

This is true but you really have to be abuseing it to melt down a 4 stroke when it is lean. It's nothing like a 2 stroke where you can toast it real quick and easy. You would have to be running it hard and long at WOT to melt one down.

[400exr]

Hey guys thanks for all your replys. Don't beat me;) , but I intalled a 170dj main on gut instinct, and shes running alot better no more stumble on the top end. Havn't done a chop test yet or raced the other 400, but I think the right direction is bigger :confused:

[cals400ex]

Originally posted by 400exr
Hey guys thanks for all your replys. Don't beat me;) , but I intalled a 170dj main on gut instinct, and shes running alot better no more stumble on the top end. Havn't done a chop test yet or raced the other 400, but I think the right direction is bigger :confused:


you may be right. like i said, i have never used dynojets before. i was just going off of what some other members on the site said. i know rico and other members that have been into the sport for a decent amount of time run the dg146 on a piped bike. if i had the kit, i would be able to give you my opinion. trial and error is all it takes. good luck

[400exr]

Originally posted by cals400ex
you may be right. like i said, i have never used dynojets before. i was just going off of what some other members on the site said. i know rico and other members that have been into the sport for a decent amount of time run the dg146 on a piped bike. if i had the kit, i would be able to give you my opinion. trial and error is all it takes. good luck

Thanks man, I'll let you know what the chop test tells me