2002 YZ250 Mods

[Duc-Monster]

I am getting to the point that I am loosing bottom end and alittle power every where else, and from what I have been told it's time for a top end.

I am looking to add performance to bike. Any help that you guys have would be great.

I am looking at a new wiseco pro-lite piston and new piston bearing, a new pipe and silencer, a VHM Head with a MX dome,and a new reed valve.

The pipes I have looked at are the Procircuit and the Doma pipe and silencer, The people from Langston racing recommend the Doma Pipe with there VHM head. I have not heard much about DOMA. Anybody?

I am at a loss as to which reeds to buy V-Force or Boyesen?

now my questions are, I would like to stay running premium pump gas. As few people told me I am going to have to run race gas! I am I going to have to rejet!

I run at about 5000 ft abouve sea level.

Thanks in advance

Pat
[email protected]

 

[bclapham]

hey Duc, cant you just shoe in a nice 996 v-twin?

i ride a 2001 yz250 and i have a couple of friends that ride the 2000 and 2001. How much different is the 2002.

as for pipes, my bike came wit the FMF SST on, it does rev to the moon but i have nothing to compare it with. if i had my choice, i would have got the Fatty since i am led to believe it has more bottom. Be careful when you buy a pipe and try to match it to your riding..... a top end screamer pipe is no good on a trail or smaller SX type track. the tracks here are quite tight and SX and since i am a begginner, i feel i would be better of with a more lower end biased pipe.....no point having a top end pipe if you cant keep it in the revs all the time!

As for reeds, at the advice of one friend i went with stock! at $16 a pair you can change them often and this should keep things crisp. He tried everything type of reed out there and went back to stock he had a lot of issues getting good jetting with the aftermarket reeds.

If you are going to change the whole reed valve, i have heard good things about tthe v-force on the YZ.

regarding pistions, i am in a similar boat being ready for a top end, so i will wait to see what comes up here.

as for jetting you will always get better results with race gas and it depends on how much performance you want (and how much you want to spend!)

My bike was fast, but never "crisp" its hot here and around 2000 feet, once i worked with the jetting the speed and crsipnesss went to a whole new level!

if you are at 6000, and you havent already worked with the jetting, give it a go.....you will be suprised!

let me know what piton info you find out!

BC

 

[dejackson]

I have a 2002 YZ250 and I wanted more bottom end and a smoother hit without losing the power on top. I run a FMF Fatty pipe with the shorty silencer, as well as the Boysen reed valve. If you want a smoother power delivery with more down low-end (4-stroke like) this is the way to go.

 

[bclapham]

I run a FMF Fatty pipe with the shorty silencer, as well as the Boysen reed valve. If you want a smoother power delivery with more down low-end (4-stroke like) this is the way to go.

i am thinking along those lines, my yz really is wild on top!

 

[MX-727]

I kind of hate replying to these type threads because it opens up "my mods are better than yours" responses, but here goes.

I have a '02 YZ250, as does my brother-in-law. His is completely stock and I had the chance to ride both bikes on the same track, the same day. I can't separate out what mods did what, because I didn't want to spend all day testing.

I had Eric do the head work, he raised the compression and changed the squish. Both mods were to compensate for my altitude (4000 ft) which is the only reason he agreed that I needed the mods. The bikes were tested at 1000 ft though with no problems.

I also have installed the V-Force reeds/block and an FMF SST and FMF shorty silencer. I run VP C-12 and have spent quite a bit of time dialing the jetting in.

My bike has a much broader powerband, and pulls much better off the bottom than his did. Where as I had to really work the clutch coming out of a couple of tight, uphill corners on the stock bike, my bike simply pulled very smoothly and quickly out of the same corner. My bike seems to pull much better and further on top also. The modified powerband feels more powerful, but there is no hit that has to be worked around. It makes the bike fun and easy to ride, especially on hard-packed turns where throttle control is so important to keep the rear accelerating without stepping out.

In short, I love the way my bike feels compared to the stocker.

 

[Duc-Monster]

727

727,

That sounds like the information I am looking for. can you tell me what Eric did to your cylinder? What piston did you use. And what did the compression ratio did you go up to. At my altitude i can actually go just a little bit higher.


Thanks

Pat

 

[MX-727]

Eric didn't do anything to the cylinder and I'm still using a stock piston. Eric felt that the porting on this bike was excellent and there was no need to change it. It wasn't even going to do the head until I reminded him of my altitude. I can't remember what the numbers are for the head and can't find my notes. I'm sure Eric could talk to you about what would work for you though. He's a great person to call and talk to and ask questions.

 

[Coop37]

MX-727 You ready for a 2003 yz 250?

 

[MX-727]

Doesn't sound like there are enough changes to warrant getting rid of the '02, but, I'm seriously considering getting the wife a '03 125.

What kind of differences have you noticed?

 

[markstir]

mx-727 what jetting did you end up with?

 

[Coop37]

I would think at this elev. 4500 ft , 172-175 main, needle and clip = n3cj-2, ( 1/2 step leaner needle) 48 pilot 1 1/4 air screw. but with real good fuel, you moght even go leaner, I ran this jetting with 90 oct fuel, and 40:1 yamalube r.

 

[MX-727]

Real close to Coop. 172, stock needle at 2nd postion, 45 pilot, between 1 and 1 1/2 on the airscrew.

 

[bclapham]

"Real close to Coop. 172, stock needle at 2nd postion, 45 pilot, between 1 and 1 1/2 on the airscrew."

i am running the same on my 2001 (nearly) i am on the 175 main but i might try the 172

 

[MX-727]

Coop and I are at 4200 ft MSL

 

[bclapham]

yes, i am only at about 2000ft but the bike was quite rich and spoogy and needed leaning. it goes much better but there is still a little spooge left. i was very worried since the stock jetting is supposed to be close but mine was always very rich! i run the SST shorty pipe combo and i wonder what effect this has!

 

[Coop37]

What gas oil ratio are you running?
Also, set the float level a little leaner, like 7.0 mm
You may have to richen the mid a bit when you do the float height?

 

[MX-727]

I tried the 170, but that really caused the bike to fall on it's face at WFO. I'm still slightly rich in the mid, but the top clip position seems to be too lean. I'm going to try the half step leaner needle.

 

[bclapham]

Originally posted by Coop37
What gas oil ratio are you running?

regular super pump gas at 32:1 with motul 600

Also, set the float level a little leaner, like 7.0 mm

thats interesting, i assume this is easily done but can it make the settings go horribly wrong or just move them a bit?

You may have to richen the mid a bit when you do the float height?

I'm still slightly rich in the mid, but the top clip position seems to be too lean. I'm going to try the half step leaner needle.

i think that is what went wrong with me also!

thanks guys

BC