YZ 450F Performance upgrades?

Yamaha YZ450F 2008

37 replies to this topic
  • riderboy1961

Posted December 02, 2014 - 09:31 PM

#21

I put the new Air/Fuel mixture screw in it today, the stock one would not fall out after unscrewing it, had to pull the exhaust off to get the float bowl cover off so I could pull the stock screw out, time consuming but got it done.

I put the stock muffler back together should have less back pressure now and has a spark arrester screen in it now.

I was able to find an 03 CDI for quite a bit less than an 06 so I will put it on shortly, hope to get that low/mid grunt I have read about on this site.

Before I start it I am going to install a 48/170 jet set, don't want the engine to run lean. I should be good to go after this. Then I need to Ride It!

Thanks for all the help on this topic everyone!!

 



  • grayracer513

Posted December 03, 2014 - 08:03 AM

#22

48/170 is a bit rich for anyplace I can think of except sea level in sub-40 degree weather.



  • riderboy1961

Posted December 04, 2014 - 09:30 AM

#23

48/170 is a bit rich for anyplace I can think of except sea level in sub-40 degree weather.

grayracer513 - Appreciate it!

    

     What do you suggest with my near stock set up? 

(ice cream cone removed from muffler, insulation removed, removed stock end cap assembly & replaced with PMB quiet core, spark arrester screen, end cap. Installed easy to reach air/fuel mixture screw 2 full turns right now. stock air intake assembly. Haven't switched over to the 03 CDI yet) 

0 - 300 feet elevation.

Winter?

Summer?


Edited by riderboy1961, December 04, 2014 - 09:31 AM.


  • Rocket416

Posted December 04, 2014 - 06:48 PM

#24

MXA mag suggests a 165 main and the stock needle in the 4th clip position from top when using an aftermarket exhaust system.

I have an 09 yz450f also and modified my exhaust similar to yours this week and will try it out this weekend. I'm using the MXA jetting specs.

I removed both ice cream cones out of the muffler and packed it with FMF 4-stroke packing. Sounds great on the stand, hoping that it's not overly loud when ripping around the track.

  • grayracer513

Posted December 05, 2014 - 07:39 AM

#25

At normal temperatures, I'd run a 165/45, but I would keep the NFPP.  Reason being that it differs from the original in that the straight section at the top is smaller, making the overall jetting between 1/8 to 1/4 throttle slightly richer.  Gives a bit better throttle response when transitioning from idle to the main circuit.  You might consider going from the #55 leak jet to a 52-50.

 

Maybe a 168 in really cold weather.  On my '06, I run the same jetting all year, from sea level (and below) to near 4000 feet with no problems.  But I don't ride in weather much colder than 30-40 degrees, either.



  • riderboy1961

Posted December 05, 2014 - 11:50 AM

#26

     I will probably leave the Needle alone for now, I don't think I have done enough to make any big adjustments yet like changing the Needle clip position. The intake is still Stock. Speaking of the Needle though... If I wanted to get to the Needle, what would be the tricks to getting to it without removing the carb? I had the full exhaust off the bike while getting to the float bowl screws but the carb did not want to spin much at all in either direction. On the YFZ450F's  (2005, 2006, 2007 Quad models) that I used to work on I was able to spin the carb quite a bit more  and I could get the Needle to pop out the top of the carb without taking the carb off.

     Leak Jet - I will have to research what this jet does exactly. Looks like going one or two smaller sizes on the leak jet are preferable with the set up I have now. 

     My stock muffler - I would have liked to put the insulation back in But, it was like holding Hair in my hand when it came out and I was not going to even Try to get it all back in where it belonged and then try to close the muffler back up, what a mess and a Surprise. I hope it is not too loud without any insulation in it.  

      Lean Situations - Is it mostly the Main Jet that handles the Lean/Rich issues? I want to make sure I don't run the engine lean. 



  • grayracer513

Posted December 05, 2014 - 01:06 PM

#27

The purpose of the leak jet is to bleed off all or part of the accelerator pump output so that it is reduced or eliminated during times when the throttle is opened more slowly or partially.  The result is a much cleaner running engine.

 

Say you put the end of a garden hose on a basketball hoop, and then cut a hole in the hose near ground level.  Without the hole, a quart of water put into the hose results in a quart coming out the top no matter how fast or slow you do it.  With the hole, you have to pump the water through a lot faster so it doesn't all leak out before it gets delivered.  Same kind of thing.

 

The leak jet causes the opposite of the normal effect in that the smaller jet results in more fuel delivered.



  • riderboy1961

Posted December 05, 2014 - 01:38 PM

#28

 but I would keep the NFPP.  Reason being that it differs from the original in that the straight section at the top is smaller, making the overall jetting between 1/8 to 1/4 throttle slightly richer.  Gives a bit better throttle response when transitioning from idle to the main circuit. 

Did you mean , keep the NFLR?  My 2008 yz450f Owner's Service Manual shows that my : standard jet needle is an NFLR.  It states if I used a NFPR in the same 3rd clip position (stock position) it would be a like raising the stock NFLR needle 0.5 position. 


Edited by riderboy1961, December 05, 2014 - 02:30 PM.


  • Rocket416

Posted December 05, 2014 - 02:30 PM

#29

You can access the needle by removing the gas tank and top motor mounts. You do not need to loosen the carburetor clamps. There are two allen head bolts holding on a cover, remove that cover and there is an allen bolt holding the needle down.

Edited by Rocket416, December 05, 2014 - 02:33 PM.


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  • grayracer513

Posted December 05, 2014 - 02:48 PM

#30

Did you mean , keep the NFLR?  My 2008 yz450f Owner's Service Manual shows that my : standard jet needle is an NFLR.  It states if I used a NFPR in the same 3rd clip position (stock position) it would be a like raising the stock NFLR needle 0.5 position. 

 

Apologies.  Probably the result of low caffeine levels this morning.  I had you mixed up with someone else who mentioned using the NFPP.  The NFPR and NFPP differ only in the diameter of the upper straight section; it's smaller on the NFPP, thus that portion of throttle opening becomes a little richer.  You can keep the NFLR and will probably be OK with it, but in an '08-'09, I find the NFPP makes enough difference to make it worthwhile.  Clip in 4.



  • riderboy1961

Posted December 06, 2014 - 10:08 PM

#31

I'm listening... I'm listening... I went to order some carb jets and the NFPP needle but I am unsure what they are calling the Leak Jet on the page I am looking at.

Does this part number (below) sound correct for a #50 Leak Jet?

                                                                                                                                  

JET (50)

FITS: 2008 Yamaha YZ450F
4JT-1494F-07-00
In Stock


  • grayracer513

Posted December 07, 2014 - 08:00 AM

#32

Yes, that's it.  it's in the float bowl.  Also, it's listed in the tuning section of your manual.



  • riderboy1961

Posted December 07, 2014 - 10:36 AM

#33

Perfect Thanks.

     Leak Jet - I had the bowl off last week and looked inside at the Leak Jet but, I could not see how it might be removed? My eyes aren't what they once were he he he, I could not see a screw driver groove on it? How is this jet removed?

     Air Filter Guide (per the manual) or Cage - I read that if we cut the mesh screen out, the motor will gain 1/2 hp? That sound correct? I took a look at mine and it is all plastic with what looks like a plastic mesh screen. If I did this I would cut the mess but but leave the ribs and reinstall? Then switch to a fire proof air filter also? The article read that the  screen is in there to keep the bike from catching fire if the carb throws a flame out the intake side. 


Edited by riderboy1961, December 07, 2014 - 07:15 PM.


  • grayracer513

Posted December 07, 2014 - 01:58 PM

#34

Removing the screen from a YZ filter guide will gain you nothing but a higher risk of fire. Doug Henry's SM team did extensive testing of intake mods and concluded that the screen is far less restrictive the filter itself, and removing it showed no measurable gains in power at all.

  • riderboy1961

Posted December 07, 2014 - 07:28 PM

#35

Removing the screen from a YZ filter guide will gain you nothing but a higher risk of fire. Doug Henry's SM team did extensive testing of intake mods and concluded that the screen is far less restrictive the filter itself, and removing it showed no measurable gains in power at all.

Cool. One less thing to do.

     Besides the OEM I found two companies (one being "Thumper Talk - parts store")  online that sell individual parts for  carburetors. I prefer to shop online unless I need something right away. Is there an area on This Site that we can discuss the places to buy parts?


Edited by riderboy1961, December 08, 2014 - 12:53 PM.


  • riderboy1961

Posted December 22, 2014 - 08:12 PM

#36

MXA mag suggests a 165 main and the stock needle in the 4th clip position from top when using an aftermarket exhaust system.

I have an 09 yz450f also and modified my exhaust similar to yours this week and will try it out this weekend. I'm using the MXA jetting specs.

I removed both ice cream cones out of the muffler and packed it with FMF 4-stroke packing. Sounds great on the stand, hoping that it's not overly loud when ripping around the track.

Rocket416 -

     How did your 09 run?



  • Rocket416

Posted December 23, 2014 - 05:40 AM

#37

Rocket416 -
How did your 09 run?


It ran good but had a louder exhaust note than I care for. It sounded like a kx450 with a stock exhaust which if you've ever heard one they are pretty loud.

I left out a little info about why I decided to modify my silencer in the first place.... The rivets had came loose and the holes in the silencer had began to elongate. So I decided to rebuild it and see how it would hold up. It lasted 2 hours before they came loose again and started blowing packing out of the seams. So I ordered an FMF Powercore 4 silencer and hope to try it out this weekend if all this rain holds off.

  • dadat40

Posted December 24, 2014 - 08:42 PM

#38

I have an 08 an am running Pro circuit to exhauste with GYTR head and am very pleased with the power it is all power all the time.
After the new head it feels very smooth and will rap to the moon.





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