Is re-jetting required??

[Vx2]

I have a 2005 400EX.

I'm still researching my exhaust options. I'm considering the White Brothers Pro Aluminum II complete system, Yosh RS-3 complete system, and FMF Q2 with Power Bomb. I will use one of these with a K&N filter.

If I change the exhaust and intake, is re-jetting required? Will the EX ride the same or worse than stock if I do not re-jet? Or will I still get more power than stock?

Thanks in advance,

Vince

[JOEX]

If you don't re-jet with those mods you'll likely reduce the life of the motor.

Re-jetting is simple to do;)

[ohsobad_chevy]

Start rich and work your way down...being too lean is NOT good!!! :eek2:

[400exrider707]

Originally posted by Vx2
I have a 2005 400EX.

I'm still researching my exhaust options. I'm considering the White Brothers Pro Aluminum II complete system, Yosh RS-3 complete system, and FMF Q2 with Power Bomb. I will use one of these with a K&N filter.

If I change the exhaust and intake, is re-jetting required? Will the EX ride the same or worse than stock if I do not re-jet? Or will I still get more power than stock?

Thanks in advance,

Vince

Any change of air into or out of the engine, will require more fuel to compensate.

[400exstud]

Originally posted by ohsobad_chevy
Start rich and work your way down...being too lean is NOT good!!! :eek2:

Being severly lean is NOT good. I prefer to run my bike a tad on the lean side just as my preference. This will not go any harm as I do not ride hard core for more than an hour at a time.

[ohsobad_chevy]

Originally posted by 400exstud
Being severly lean is NOT good. I prefer to run my bike a tad on the lean side just as my preference. This will not go any harm as I do not ride hard core for more than an hour at a time.

LOL...that is helarious. "Do not ride for more than one hour at a time." You are not gaining anything from running your quad a little lean, you should richen it up a little bit, make it run a little cooler and you can ride longer without it getting too hot. :ermm:

[JOEX]

Originally posted by ohsobad_chevy
LOL...that is helarious. "Do not ride for more than one hour at a time." You are not gaining anything from running your quad a little lean, you should richen it up a little bit, make it run a little cooler and you can ride longer without it getting too hot. :ermm:
I've heard a leaner mixture will net more HP but at the expense of wear on the motor. It may work for the avid racer who rebuilds often but not for the average rider. I don't have any details but i've heard this more than once and not from your everyday yahoo:p

[AR15 guy]

Leaner is meaner. Until it goes boom.

[GPracer2500]

Power, heat, and air/fuel ratios combine into one helluva complicated subject. I'm still learning the many details....I'm confident that someday I'll have a "complete picture" about what, when, where, how, and why things happen inside a combustion chamber. Until then, I'll just share what I think I currently know:

The best air/fuel ratio for maximum power in a gasoline engine works out in practical tests to be around 13:1 (air to fuel, by weight). The stochiometric ratio for gasoline is 14.7:1. This is the ratio that allows for complete combustion of all the fuel and all the oxygen in the intake air. An engine also produces it's highest exhaust gas temperatures with that ratio. Going leaner than 14.7:1 (larger numbers are leaner) will actually bring EGTs back down from their peak. Note that the 14.7:1 ratio only really holds under laboratory conditions. Your average pump fuel generally will have a stochio slightly lower (richer) than 14.7:1 because of the additives in modern fuels.

The reason why slightly richer than 14.7:1 is best for max power is primarily because 1) a mixture between about 12:1 to 13:1 burns fastest within the combustion chamber. 2) As fuel is vaporized in the carb venturi it absorbes energy, lowering temps, and creating a denser charge. Combine those factors with the (somewhat less significant) fact that most fuels aren't really stochio at 14.7:1 and around ~13:1 works out to be the "best" ratio for maximum power. So, if you accept 13:1 is the threashold between lean and rich, then max power will come right at the threashold of lean and just a little before EGT peaks (i.e. slightly rich from peak EGT).

But there's so much more going on that needs to be considered. EGT isn't the end-all-be-all parameter for overall engine temp. The temps of the valves, cylinder, piston, head, etc. will certainly go up and down with EGT, but there's other factors at play. An extremely important one is the boundry layer of air/fuel mixture that clings to all the metal surfaces inside the combustion chamber. The boundry layer is just unburned mixture (in gaseous form) that "hangs out", mostly stagnant, on every surface. If you look at a piston that's been run lean it will appear clean and reletively free of carbon deposites (unburned or partially burned fuel)--the boundry layer barely had a foothold. A piston run rich will have lots of carbon deposites. These deposites are related to the presence of the boundry layer. Deposites collect where the boundry layer is strong and undisturbed. The layer is very thin but acts as an effective insulating barrier between the very hot combustion gasses and the comparitively cool metal of the piston, head, cyl, etc.

The more lean a mixture is the more of that boundry layer gets consumed under normal combustion. Also, if any deto takes place from running borderline lean than the boundry layer gets completely blasted away. That's the mechanism that allows deto to errode away piston material. Once the boundry layer becomes compromised the EGT actually goes DOWN as engine temperatures go UP. This is because heat from the combustion gases is being absorbed into the engine rather than exiting with the exhaust.

A rich mixture runs cooler because 1) like I said above, when the fuel is vaporized in the carb it absorbs energy, lowering charge temps. And 2) when some fuel is left unburned after combustion then that unburned fuel absorbes some heat from combustion. That lowers the total net temperatures generated during combustion. This is the same process that causes a way too lean mixture to run cooler than stochio. If there is unburned oxygen left over after combustion than that oxy gets heated (but not ignited) up by the stuff that did burn and the net temps go down.

So, once you establish exactly where lean begins and rich ends (13:1 in this context) than max power comes right at that threashold. Go leaner and engine temps will breifly continue to rise (as peak EGT is reached) and then may rise further because of boundry layer disturbance and abnormal combustion (deto). If no abnormal combustion takes place than temps will go down and continue to cool off as you go so lean the engine will no longer run. Go richer and the engine will run cooler and make less power.

On some air cooled engines, the engine might not have enough cooling capacity to ever really get to an ideal air/fuel mixture for max power. As you pass through 11:1 and 12:1 (going leaner as power keeps going up) you may reach a point when the engine just can't handle the heat. You may not ever reach the ratio that would allow for the best power because engine longevity is so drastically reduced do to its inability to handle the heat. AFAIK, the EX engine is capable of handling the heat of a "best power" air/fuel ratio as long as proper precautions are taken.




ETA: Yikes...I didn't mean that to be so long. Props to anyone that actually reads it! ;)

[Vx2]

Thanks for all of the replies. I will do all three at the same time. I'm going to install the filter and exhaust. Then I'll bring it into the shop to have the re-jetting done.

Thanks,

Vince

[Vx2]

So I have decided on the Yosh full system and the dealer recommended the K&N power up pack, which includes the air filter and jet kit.

I'm going to have the dealer install the jet kit and air filter. But the next appointment isn't until August 5th. So can I install the Yosh and ride without any problems? Or should I just wait until all 3 things are installed?

Thanks again,

Vince

[Honda#4]

wait untill u have all three things,when u buy a pipe u have to rejet but the only pipes ive seen that u can run on stock jetting is the wb e-series but everyone tells u to rejet cus u get more out of the pipe.so just wait untill u have all the stuff first.

[buster024]

My advice is to do the entire install yourself. I'm fairly new to atv'ing, and know little or nothing about engines, but I was able to do it, and I learned a TON about my bike. I've got a Yosh system, k&n, and have re-jetted. You'll be so happy you did it yourself, and it will save you some bucks. There is 100 different threads on this site to tell you exactly how to do it, and if you get stuck, just ask!!!
I've re-jetted and fine-tuned my bike 4-5 times now, and I can have the carb torn out of my bike and back together again in about 15 minutes or less. The pipe (and headers if you are getting those too ((recommended by the way))) is super easy to install, k&n takes about 2 seconds, and the rest is just a learning curve. You won't screw it up if you take your time, ask lots of questions, and search the 400ex forum for some answers!!

Hope you do it,....
Good luck!!

[buster024]

oh, and GP...that was a freakin epic!!!
Awesome, but holy cow!!

[GPracer2500]

Originally posted by buster024
oh, and GP...that was a freakin epic!!!
Awesome, but holy cow!!

I get a little carried away sometimes...;) I'm just glad to know that someone actually read it!

[GPracer2500]

Originally posted by buster024
My advice is to do the entire install yourself. I'm fairly new to atv'ing, and know little or nothing about engines, but I was able to do it, and I learned a TON about my bike. I've got a Yosh system, k&n, and have re-jetted. You'll be so happy you did it yourself, and it will save you some bucks. There is 100 different threads on this site to tell you exactly how to do it, and if you get stuck, just ask!!!
I've re-jetted and fine-tuned my bike 4-5 times now, and I can have the carb torn out of my bike and back together again in about 15 minutes or less. The pipe (and headers if you are getting those too ((recommended by the way))) is super easy to install, k&n takes about 2 seconds, and the rest is just a learning curve. You won't screw it up if you take your time, ask lots of questions, and search the 400ex forum for some answers!!

Hope you do it,....
Good luck!!

I agree with this 100%. You'll be soooo much happier learning to do it yourself.

[buster024]

I'm just glad to know that someone actually read it!

LOL I actually showed my wife your post to show her that I'm really not looking at porn all day, and I'm actually learning something!! I'm going to use "stochieometric" on someone as soon as possible!!