Power Valve Springs

[celler]

I noticed in the parts diagram that the 250 has a single spring while the 300 uses two springs. It all depends on the spring but I would guess the 2 springs on the 300 allow for a slower rate of opening. Looks like another tuning option. Twowheels - no pressure but since you are a dealer seems you could give it a try and report back I can tell you that the little I did ride my 250 it makes my 250 SX feel mellow in the midrange. The SX is still quite a bit stronger way on top (Rarely usable). Not saying the Beta is peaky but just a lot of power quick. I'm going to love it in the sand. The two springs may be quite useful on a 250 to slow the rate of rev. for slick conditions.

[Knox Enduro]

On my 250('13) I found the same thing, and after some experimenting I did the opposite of everyone else and turned the PV adjuster out to flush. This allows the PV to start opening sooner, softening the bottom and making a smoother transition to full open.

[twowheels]

I noticed in the parts diagram that the 250 has a single spring while the 300 uses two springs. It all depends on the spring but I would guess the 2 springs on the 300 allow for a slower rate of opening. Looks like another tuning option. Twowheels - no pressure but since you are a dealer seems you could give it a try and report back I can tell you that the little I did ride my 250 it makes my 250 SX feel mellow in the midrange. The SX is still quite a bit stronger way on top (Rarely usable). Not saying the Beta is peaky but just a lot of power quick. I'm going to love it in the sand. The two springs may be quite useful on a 250 to slow the rate of rev. for slick conditions.

Hmmm ... I'll add that to my list of things to try. I had played with the PV some earlier in the year and found that the stock setting on my 250 worked the best all-around. A half turn out would have been good for faster races, a half turn in almost felt like a trials bike ... at the revs I ride. My preference is to have a torquey bottom with a bit of a snap and then a strong top.

I had a colleague once who explained things by examining their extremes. If you apply that to the powervalve spring preload, you could imagine that at zero turns the powervalve would open most easily, thereby eliminating any hit by essentially fixing the exhaust port in the highest position. Lazy on the bottom, but no hit either. If the spring was of infinite stiffness, or in this case turned all the way (3 turns max per Beta iirc) in, then the exhaust port would remain low. The bike would be super torquey (and possibly abrupt) on the bottom, then run out of breath very easily. I think what guys are perceiving as 'hit' is the transition from closed to open, and an earlier opening PV is a loss of low end that makes it seem smoother.

Still we'll test ... maybe I can get WallyBean to help source some springs

[Mxdave]

I went in a turn on my 14 250rr on the PV, it was just too peaky on standard for racing I found (Well not raced it yet). More armpump and less control with it Pv opening soon for me but we ride a lot of gnarly single track.

Go pro flattens everything out can't seen see the roots and bumps.
http://www.youtube.com/watch?v=u1O2HjZt1iw

[Knox Enduro]

I did test the extremes, best way in the beginning to notice effect. I also ride gnarly single track(Tennessee Mtns), but I did my testing in a flat open field to take out the variables.
When I went in to the max the power was very abrupt off idle and then it seemed with increased rpm the PV would overcome the spring all at once, hence the "hit". When I turn it out to flush or maybe a little beyond, I guess the PV is a little open at low rpm, taking away a little bottom and the abrupt power then power builds quicker but more linear. This in combination with an auto clutch makes for a very smooth bike.
I am obviously the only one with this opinion, but I am more likely to try things for myself than just go by what I read, and this set up works for me, but everyone is different.

GP

[Knox Enduro]

BTW, this is some of the same principal we learned from Wally Bean and his PV spring assortment on the wr125.

[twowheels]

I did test the extremes, best way in the beginning to notice effect. I also ride gnarly single track(Tennessee Mtns), but I did my testing in a flat open field to take out the variables.
When I went in to the max the power was very abrupt off idle and then it seemed with increased rpm the PV would overcome the spring all at once, hence the "hit". When I turn it out to flush or maybe a little beyond, I guess the PV is a little open at low rpm, taking away a little bottom and the abrupt power then power builds quicker but more linear. This in combination with an auto clutch makes for a very smooth bike.
I am obviously the only one with this opinion, but I am more likely to try things for myself than just go by what I read, and this set up works for me, but everyone is different.

GP

The auto clutch adds an entire additional layer of complexity, because it's engagement is also rev related.

[GMP]

I'd bet the assortment of KTM springs drop right in if you have them and want to experiment. The Beta PV system is a cross between the GG design (sub port drum valves) up top, and the KTM governer on the bottom.

We forget that 2strokes had hit before powervalves. Can you say Suzuki TM400?

[mtdirtbag]

Glenn, that wasn't hit - that was a toggle switch on the right handlebar!

[celler]

The first ride I did was about 60 miles. I did try various power valve setting from flush to 2.5 in. It appeared that I lost some low end when flush. It responded to the clutch very well but overall I was not smooth. At 2.5 in it just delayed the midrange. I ended up at the stock 1.5. I think my jetting was a little lean on the needle so next ride I will richen that and go to 2 turns. This set up felt good in my lawn test....

I'll do a ride report after I get more rides in.