450R main jet

[Karizz]

Man, I was just going thru the Factory parts catalog ....and the 450R only comes with a 118 main jet. Man thats lean.My YFZ was the same way, it was waaaay lean from the Factory.
So I ordered a 128 and a 130 so I can start tinkering after a few rides. Im gonna pull out the exhaust baffle,remove or modify the airbox lid and rejet.Oh yeah what the hell is the heater for in the carb? Hot start? WTF?

[chad502ex]

Originally posted by Karizz
Man, I was just going thru the Factory parts catalog ....and the 450R only comes with a 118 main jet. Man thats lean.My YFZ was the same way, it was waaaay lean from the Factory.
So I ordered a 128 and a 130 so I can start tinkering after a few rides. Im gonna pull out the exhaust baffle,remove or modify the airbox lid and rejet.Oh yeah what the hell is the heater for in the carb? Hot start? WTF?

i also noticed the heater, wtf?



chad502ex.com:confused:

[Fred55]

Its for cold weather riding, and/or ice racing.

[2004TRX450R]

Originally posted by Karizz
... the 450R only comes with a 118 main jet. Man thats lean.My YFZ was the same way, it was waaaay lean from the Factory.

You can't tell anything about it being lean or rich by seeing it has a 118 main. There is WAY more to it than that. It probably has a 3 jet carb that basicly has 2 mains in it. One for mid to full throttle and one for full throttle. The way the passages in the carb are set up and just overall design of the carb have more to do with it than the main jet size.

[RobRacing]

No carb has 2 main jets. The three basic jets are the pilot (slow) jet, needle jet and main jet. The pilot controls 0 to 1/4 throttle, the needle controls 1/4 to 3/4 throttle and the main covers 3/4 to wide open. The needle jet affects the whole jetting range so changes to the clip postion affect everything. As far as having a 118 main jet doesn't mean its lean. The only way you are ever going to know is if you hear it run.

[2004TRX450R]

Originally posted by RobRacing
No carb has 2 main jets.

Hm I guss you haven't been in the motorcycle industry long then. There are lots of carbs out there that have 3 jets being pilot, and two mains. You don't really see them much on ATVs or Dirtbikes but more so on street bikes and some sleds. I belive the old Yamaha Phazer Snomobiles have them.

[RobRacing]

How would a carb like that work then. i.e. fuel transfer

[2004TRX450R]

It's basicly just like any other carb just it has another main that will help make more precise fuel mixture ratios in the transition from the needle to the main jet at around 3/4 throttle. I have all the notes from MMI on it but they are at work so I can't quote them here now. But trust me there is such a thing.

[Pahrump]

Originally posted by 2004TRX450R
It's basicly just like any other carb just it has another main that will help make more precise fuel mixture ratios in the transition from the needle to the main jet at around 3/4 throttle. I have all the notes from MMI on it but they are at work so I can't quote them here now. But trust me there is such a thing.


There is such a thing but it is not common and this is not how the carb on the TRX is designed.