my 2008 yz450f race prep

Ok I have a race to go to this weekend. It will be the first race on the new 2008 yz450f. Here is a list of things I am planning to do before the gate drops...

1. Change my rear sproket to a 51T

2. Remove stock exhaust and add a 2007 full Yoshimura system

3. Richen up the pilot and main jets, add fuel screw and turn it 2.5 out

3. Add the quick turn cam throttle system

My question is on the jetting. I know I ran a 48/168 on my 07 and it worked wonders. Whats stock jetting and what effect would changing the exhaust sytem have on the stock jetting? Will it richen up the bike or make it leaner?

I was thinking about running a 48 pilot and a 170 main. Will this be too rich at sea level?

I guess it depends on the stock 08 jetting and how much richer or leaner the Yosh system will make it.

Haven't you rode you're new bike yet? If so seems like you would know if it was running lean. Personally, I wouldn't make too drastic of changes on the jetting before going out and racing it.

Make your changes first, then jet to suit. That's really the best way to do it. I don't think it is a must that you will need to adjust your jetting unless the pipe throws it off that bad. If i were you, i wouldn't rush it. Install your exhaust and ride the bike and see how it performs, if you don't notice anything funny then leave it for the race. I think if you are pressed for time then the jetting shouldn't be rushed unless necessary.

Ok im pretty much ready for the weekend. I got the Yoshimura pipe put on with the original head pipe. I jetted the bike to a 48 pilot and a 165 main jet added the air screw (2 turns out). I had to remove the motor mount brackets to be able to turn the carb enough to get the jets in and the ajustable air screw, but after you do it a few times its cake. I added the quick turn throttle and it definately seems like thats going to make a huge difference. I also took all the play out of my throttle to help the cause. I cut 2 inches off both ends of my stock pro taper bars. I added the 51 tooth sprocket.

It took about 10 kicks to get it to fire up but let me tell you when it did it was music to my ears and nose. It sounded like one bad ass bike now. It was late so I wasnt able to run it but, the throttle was definatly responsive.

I will keep you posted as soon as I can take it for a rip.

Did you put the full RS-2 system on or just a slip on? I ask since you said that you put it on the stock header. From what I read you really need full system to get the most out of it since the stock header is to large in diameter.

I cut 2 inches off both ends of my stock pro taper bars.
2" off BOTH ends? Why so narrow? Curious....

yeah, 4" off the bars that seems extreme to me.....

what kind of race are you attending?

if you racing MX why go so big on a rear sprocket? wouldn't you want more acceleration, since you will most likley not be going the top speed.

what kind of race are you attending?

if you racing MX why go so big on a rear sprocket? wouldn't you want more acceleration, since you will most likley not be going the top speed.

The bigger rear sprocket gave it more acceleration.

Its a full Yoshimura rs2 titanium, I made a mistake I only cut 3/4 of an inch off the bar ends on each side. I also use Fastco anti vibration inserts.

I am running VP 4.2 race gas.

I must have been sleepy sorry for the misunderstanding.

UPDATE - After running it today it still sounds a little bit on the lean side. I am going to drop a 170 main in it from 165 and see how it works.

The bigger rear sprocket gave it more acceleration.

you right...my bad i got it all confused with the front sprocket :thumbsup:

you right...my bad i got it all confused with the front sprocket :thumbsup:

I didnt think people from China said "my bad"

:ride:

Now this is the bike I was hoping it would be. Not only does it corner great now its is amazingly fast. It is much faster than my stock 07 was for sure.

Now this is the bike I was hoping it would be. Not only does it corner great now its is amazingly fast. It is much faster than my stock 07 was for sure.

Would you happen to know what all the changes yamaha did to the 08? and is it possible to make a 07 corner like a 07?

All '07's like '07's as far as I know, ( :thumbsup: ) but if you want it to handle like an '08, here's what I know about it.

Some of the improvement is in weight, but only about two pounds. OTOH, the weight came from the steering head, and the muffler, both of which are high and toward one end, rather than near the center and low.

The frame geometry was not changed at all, but the steering geometry was. On an '07, the head angle is listed as 26.8 degrees, and the trail is 114.1mm. This is steeper and shorter than the '06, which is 27 and 115.6. Pulling the forks up on the '06 accomplishes the same thing that Yamaha did to the '07 by increasing the rear shock length.

The '08 is 26.9 and 115.2. This is pretty much exactly what you would get on an '07 if you installed 24mm clamps.

Beyond that, rider position and set up (sag, etc.) and suspension are very important to making the late YZF work right. The chassis seems unusually sensitive to small adjustments.

All '07's like '07's as far as I know, ( :thumbsup: ) but if you want it to handle like an '08, here's what I know about it.

Some of the improvement is in weight, but only about two pounds. OTOH, the weight came from the steering head, and the muffler, both of which are high and toward one end, rather than near the center and low.

The frame geometry was not changed at all, but the steering geometry was. On an '07, the head angle is listed as 26.8 degrees, and the trail is 114.1mm. This is steeper and shorter than the '06, which is 27 and 115.6. Pulling the forks up on the '06 accomplishes the same thing that Yamaha did to the '07 by increasing the rear shock length.

The '08 is 26.9 and 115.2. This is pretty much exactly what you would get on an '07 if you installed 24mm clamps.

Beyond that, rider position and set up (sag, etc.) and suspension are very important to making the late YZF work right. The chassis seems unusually sensitive to small adjustments.

Actually I have already edited the post one time because I put 06 instead of 08 and still messed up by putting 07:bonk: . Anyways so the 07 will handle like the 08 with 24mm clamps? and will the 06 handle like the 08 with 24mm clamps.

The steering geometry will be very similar set up that way, if on the '06, you also pull the forks up about 5-7mm.

All '07's like '07's as far as I know, ( :thumbsup: ) but if you want it to handle like an '08, here's what I know about it.

Some of the improvement is in weight, but only about two pounds. OTOH, the weight came from the steering head, and the muffler, both of which are high and toward one end, rather than near the center and low.

The frame geometry was not changed at all, but the steering geometry was. On an '07, the head angle is listed as 26.8 degrees, and the trail is 114.1mm. This is steeper and shorter than the '06, which is 27 and 115.6. Pulling the forks up on the '06 accomplishes the same thing that Yamaha did to the '07 by increasing the rear shock length.

The '08 is 26.9 and 115.2. This is pretty much exactly what you would get on an '07 if you installed 24mm clamps.

Beyond that, rider position and set up (sag, etc.) and suspension are very important to making the late YZF work right. The chassis seems unusually sensitive to small adjustments.

What about the mags saying there is more flex in the stearing head, which in hand makes the front stick better

I was sitting here watching re run of steel city race and they where talking about the "flex" in the frame that was changed for 08, is this where head was cut and lightened?

That is where the head and the gusset work was reduced, but that won't help the front stick better. It may make the ride feel less harsh, but the flex in the frame is insignificant compared with the suspension. Decreasing frame stiffness is only something that would be noticeable as a reduction in road shock, or when the handing begins to suffer because the wheels will no longer stay in their proper place because of it.

It won't do anything good, but if it was stronger than it needed to be in the first place, it won't do anything bad, either.

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