Correct me if im wrong...

6 replies to this topic
  • wrdatk

Posted September 28, 2010 - 01:20 PM


2 weeks ago I picked me up my first bike, 2003 yz450

Not only my first purchased bike but also the first time ive ever ridden one, so I'm new to all this but ive been working as a auto/marine mechanic for over 5 years now

It has a white brothers full Ti exhaust, now the bike has a lot of aftermarket stuff on it but I do think it has the stock jet size

This is where the correct me if I'm wrong part comes in, if you decrease back pressure you have to increase jet size right? and in my case what jet size would be best...the wb muffler is essentially a chery bomb glasspack like I have on my mustang haha

the bike has an aftermarket high flowing air filter setup as well

is there anything else that I can/should do to feed this beast some more fuel

Thanks in advance

  • tech24

Posted September 28, 2010 - 01:27 PM


How does it run? If it runs good it may have be re-jetted

Generally you'll need 1 size larger main, the needle can probably be left alone and turn the fuel screw out a tad probably 2 turns out from fully closed. I use dyno jet kits so I may be a little off when using Kehin stuff.

  • wrdatk

Posted September 28, 2010 - 01:30 PM


it runs good however at 75% throttle and up it starts popping like its starving for fuel....not extreme though

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  • tech24

Posted September 28, 2010 - 01:36 PM


I edited my first post was tyring faster than thinking but anyway, it sounds like it may have too large of a main in it already.

You can take it out and see or get a jet kit and be done with it, thats what I do cause I hate carbs. Dynojet is usually spot on, I see JD recommened a lot Someone else will chime in will advice!

  • sacfelix

Posted September 28, 2010 - 02:01 PM


What is the current jetting?

  • grayracer513

Posted September 28, 2010 - 02:15 PM


This is where the correct me if I'm wrong part comes in, if you decrease back pressure you have to increase jet size right?

Not necessarily, no. In fact, it may be the opposite. Improving the airflow through the engine may increase the strength of the intake vacuum signal and cause the engine to run rich.

The stock muffler is also a straight through, fiberglass packed type, so there isn't necessarily a great deal of difference, jetting wise.

Check out these three threads:


  • wrdatk

Posted September 28, 2010 - 03:30 PM


hmm the threads by Eddie Sisneros are very informative, ill have to mess with it tomorrow when i get off work

thanks grayracer513 for posting them and everyone else for the help, ill report back tomorrow

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