Pilot Jet/Fuel Screw


2 replies to this topic
  • roylo

Posted July 05, 2009 - 06:21 AM

#1

I have an after market muffler fitted to an otherwise standard 08 YZ450F. The bike seems to run very good. The jetting has been richened to a 168 main jet and needle 1 clip position richer from standard. Pilot jet is standard. Ive found the optimum setting of the fuel screw to be 2 1/2 turns out. Does this mean I should go 1 size bigger on the pilot jet and re-tune the fuel screw?

My main question is if I have the 45 size (standard) pilot jet fitted and tune the fuel screw to where it runs best as explained above, then fit a bigger (48) size pilot jet and re-tune the fuel screw will there be any difference to the overall tune of the engine?

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • ace402

Posted July 06, 2009 - 06:04 AM

#2

I'd leave it. If it has to be readjusted more than 2.5 turns then swap for the richer main

  • wondermuscle

Posted July 06, 2009 - 07:20 AM

#3

I have an after market muffler fitted to an otherwise standard 08 YZ450F. The bike seems to run very good. The jetting has been richened to a 168 main jet and needle 1 clip position richer from standard. Pilot jet is standard. Ive found the optimum setting of the fuel screw to be 2 1/2 turns out. Does this mean I should go 1 size bigger on the pilot jet and re-tune the fuel screw?

My main question is if I have the 45 size (standard) pilot jet fitted and tune the fuel screw to where it runs best as explained above, then fit a bigger (48) size pilot jet and re-tune the fuel screw will there be any difference to the overall tune of the engine?


It depends on temperature for me and my bike. I run a 168 main, 45 pilot and the clip one richer. I had a 48 pilot in the bike and found that it ran fine but starting the bike when hot was much more difficult. Also, if you turn the fuel screw in with a 48 I found that you could screw it all the way in and the bike would not die, thus the jet was too big/rich. I'm not getting any popping with the 45, so it stays in for now.

I plan to run the 45 for the summer and this winter put the 48 back in when the air is bit more dense.

good luck





Related Content

Forums
Photo

Chubby dad, looking at bikes , First trip to the orange/black forum ! by Slow_ride


Dirt Bike   Make / Model Specific   KTM   250-530 EXC/MXC/SXC/XC-W/XCR-W (4-Strokes)
  • Hot  28 replies
Wiki
WR Camshaft Swap Info - last post by jamesm113

WR Camshaft Swap Info


Articles
  • 0 replies
Forums
Photo

2016 YZ450 by CaptainKnobby


Dirt Bike   Dirt Bike Technical Forums   Suspension
  • Hot  59 replies
Forums
Photo

Michigan Motocross Tires by 288yz450


Dirt Bike   Dirt Bike Regional Discussion   North
  • 1 reply
Forums
Photo

James Stewart back on a YZ450F by YamaLink


Dirt Bike   Special Interest Forums   Pro Racing
  • Hot  47 replies
 
x

Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.