2003 yz 125 "go fast" needle???

Jman271 · Jan 25, 2004

:thumb: Does anyone here recall a "go fast" needle that had been circulating around as an improvement over the stock weird taper needle? Also, does anyone have a a good jetting set up they care to share? Tried the search bar, only a few popped up,,,,

steve125 · Jan 25, 2004

J-Man I'm not aware of this go-fast needle :scream:

The 03 YZ 125's 38 carby is spot on from the factory. Maybe try a leaner main in warm temps, depending on the fuel used.

The real trick is to do something about the intake manifold. It has a nasty internal drop down from the top into the reed area. Not good at all :eek:

Jman271 · Jan 25, 2004

Yeah, I can see what you mean, it looks like the carb is shooting up into the reed block, then it shoots down, like there is a large void in the maniflod molding. There is a v-force on it now, and there is some mis-match between the manifold and reed block so I will fix that. The "go fast" needle supposedly made an improvement, but from what I remember, it was like an update or something, I don't know, maybe I'm on crack,,, I will call around to see,,,,I just compaired stock CR w/ claimed, it was about 8.5:1, claimed was 8.7:1. I took a few thou off the head to get it w/i spec. The guy wants to run pump gas so I can't go much past 8.7 w/ running into problems. Squish was about 1.23, w/a .010 deck height, it gave me below spec MSV, but w/o taking .020 off to get squish around .8 and about 15msv, I will have to re-cut the bowl a boat load to remove enough material to get CR back to 8.7. If I have to go that route, I would rather do a flat top w/ this set up, but he is on a budget,,,,,,,thanks for your info though! See ya-

bclapham · Jan 25, 2004

Jman- the problem might be the v-force. FWIW the reed block bolts up the same as the rm reeds, but the entrance hole is about 3mm's off (vertically)- so the v-force is the same model for both bikes and thats why its all jacked up.

i would consider going back to the stock setup, ive had the "V" on both my rm144 and yz250 and both ran rich from 0-1/2 throttle, and both were a major pain to jet out- everyone says the v-force is the hot ticket on many bikes, but i wonder if they just run too rich and then give a bit of a hit at the higher throttle opening and people think by the butt dyno the bike is making more power???????

one thing to consider is the manifold- the RM manifold is a lot straighter than the yz, but i dont know if the carb would fit etc i have a stock yz reed cage and a rm manifold with the stuffers cut off that can be used with the above- i sent them to marcus though, so you might have to wait a couple of weeks if you want to try them.

btw- dont forget to shim out the PV governor spring- now theres a cheap mod!!!!

va_yzrider · Jan 26, 2004

Where can I find the shim for the PV? Are they made by Pro Circuit? I've looked around and can't find a supplier or any information on the Pro Circuit site.

Jman271 · Jan 26, 2004

:think: I have heard of the PV spring, but don't know much about it, is this for the PV assembly, or the gov off the crank? What does it do? Allow more blow down @ low rpm? What gives?

MXP1MP · Jan 26, 2004

What I ended up doing on my '02 yz 125 was replacing the stock dual tapered needle to one that wasn't. I can't remember the needle # now but I can look it up. I thought you could just swap to the '04's parts and get the same effect as the PC setup.

Jman271 · Jan 26, 2004

I called and order 3 of them, they are PV spacers, they are $3.95, if you call them ask for Terrance, he was very helpful. I will post a report on how they work.

bclapham · Jan 26, 2004

Jman, there is a really good simple mod you can do for that bike- mount the V-force into a vice, then give it a real good smack with a 15lbs lump hammer, one good heavy blow should do the trick.

look at marcus's 04rm125 tuning thread for info on the YZ pv shims

steve125 · Jan 26, 2004

The best way to update the PV spring for the 01-03 YZ125's is with one from the 00/04 part number. It's the same. I believe the new spring was around $5-10 bucks. It's also a good idea to get a new side cover gasket.

va_yzrider · Jan 26, 2004

Jman, who did you call to order them?

yz250flash · Jan 26, 2004

I have a '01 yz125 and was wondering if the PV mod needs to be done to my bike. It seems to run well, what does the mod effect? If it will help, how is it done? Also, what does the needle change that jman is referencing change?

steve125 · Jan 26, 2004

Yes the PV spring mod should be done to your 01. I perfer just replacing the spring with the updated one from Yamaha.

Yamaha for 01-03 lightened the Pv spring rate, this causes the PV to open to soon and can create a bog like feeling or dip early in the powerband.

For 04 Yamaha went back in time to the 00 PV spring and solved this problem.

Just follow your owners guide on how to remove and install. It's your choice wether you add shims to pre-load the std. spring or just get the correct one and install it.

Also on your 01 jetting, it would be a good idea to update it to the 03 -04 spec. Yamaha has made big improvements with it's late model jetting for the 125.

Jman271 · Jan 26, 2004

va_yz, I called Pro Circuit direct. They also recomended the following jetting which I will try. 430 main,(410 stock), needle 2nd,(stock 3rd) 37.5 pilot,(stock 40), and 1.5 on a.s.,,,from what I hear the PV spacer is supposed to help power delivery, but this is hearsay, don't really know if it applies to just 03, or if 01 can benefit as well, call them and ask. Hey for $4, it's worth a shot!!!

va_yzrider · Jan 26, 2004

Thanks, I've heard about the spring being too soft and thus causing the PV to open early on the 01 model. I think I'll give it a shot with either the '04 spring or the spacer. The jetting specs seem close to what I've got now (except I'm a little larger on the main), but I'm using a Pro-Circuit Platinum pipe and shorty silencer (probably why I needed a larger main).

yz250flash · Jan 26, 2004

steve125 - thanks for the response. I will look it up tonight. The bike runs strong but does seem to have a slight bog on low end. If the new jetting is anything like the ones jman noted I wouldn't be able to run them. I am currently running a 27 PJ (one up from stock), needle in position 2 and a 450 main. This seems to be right on.

yz250flash · Jan 26, 2004

I just called ProCircuit and they sold their last two spacers today! Someone here probably got them. How deep into the motor do I have to go to change the spring? I look at a schematic and it looks like a lot more trouble to change the spring than it is to just put in a spacer.

va_yzrider · Jan 26, 2004

To change the springs (I believe there are two of them, someone correct me if I'm wrong) you will need to remove the cylinder and disassemble the PV. It is a bit of work and it is a little tricky getting the PV back together correctly. The advantage is that you get to clean the PV while your at it, hehe. I may wait until I need to do the top end again to save a little work.

Looks like Jman beat us to the punch!

steve125 · Jan 26, 2004

Spring or spacer(shim) the procedure is the same. You need to remove the right side cover and this can be done with the engine in the frame. This mod only concerns the PV governor that is in the right side outer case half. No need to fool with the top-end. Check you owners manual it shows how.

Also some of your bog could be that 01 jetting. I'm sure it's pricey to update the carb spec, as most of the jets need to be changed.

Jman271 · Jan 26, 2004

If PC can't get any more, I will copy the shim thingy and get you the specs, you can make your own or whatever, ya know???

va_yzrider · Jan 27, 2004

steve125, you're right. I was thinking of the torsion springs on the PV rod assembly. It is, in fact, the governor compression spring which you can access from the right side. This should be a much easier fix. The spring is $2.19 from Yamaha of Troy.

yz250flash · Jan 27, 2004

I ordered the spring this morning from my local shop. I read an article this morning about the '04 yz125 and one thing they mention as a little improvement that made a big difference was the Governing Spring. Below is a link to the article if you would like to read it.

http://www.motocrossactionmag.com/detail.asp?id=1037

steve125 · Jan 27, 2004

Good to see you guys are on track :thumb:

Don't forget a clutch cover and side case cover gasket, sometimes they tear upon removal.

MXFastGuy · Jan 27, 2004

Anybody have the part # for the spring?

yz250flash · Feb 1, 2004

MXFastGuy said:
Anybody have the part # for the spring?

It is 90501-30001. I replaced mine this weekend. Pretty simple to do. It is really easy if you have two people, then you can compress the spring on the governing assembly while the other person pulls the pin. This allows you to keep the wholle top part of the assembly (the part with the ball-bearing) together. You can just lift the whole top part up off the spring, put the new spring in, then compress it all again and replace the pin.

I didn't even remove the clutch cover, just the right side outer case. I just unhooked the clutch cable, loosened the bolt that holds the clutch actuator in place and pulled the actuator up.

The worst part about the whole operation was removing the coolant. I always manage to spill some.

I can't believe that this little $2 spring made such a difference but it seems to have taken care of the small bog that I have been trying to jet out forever. No hesitation in it at all now.

Thanks for the tip on this guys. In my opinion this is a cheap and pretty simple upgrade that should be done. Even if you do it and don't think it has helped your bike, you are out a whole $2 and about an hours time.

2003 yz 125 "go fast" needle???

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