Power Valves

[WilDun]

I'm beginning to become interested in bikes again (after a twenty years or so layoff) . I more or less bowed out just before power valves became popular on two strokes, so I'm not really familiar with these - but I do know the basics.
Seems that there are at least two different types, and I'm looking for descriptions and information on their operation and their affect on performance, also, how they affect expansion chamber design.
Any of you young wizz kids have some ideas on where to look?
- Thanks.

[Faded]

[Only registered and activated users can see links. ] and then select "Two-Stroke Exhaust Valves Tips and Tuning". Good luck.

[super rat]

got back into riding after 23years last year. Got a cr125 and what I notice is that when it hit the pipe it seems to hit harder and a lot longer,will wake you right up.

[WilDun]

Thanks for the replies,- The Eric Gorr stuff looks like it's got a lot of info.

Unfortunately, at 61, I don't think that I'll ever be riding again, - I had a fractured spine a few years back ( not bike related), and the old arthritis has set in, (I doubt if I could even throw a leg over a bike now, let alone ride it!) - I just want to play with engines and let somebody else have all the action (and fun. )
The bike bug never goes away

[powerchord1989]

BTW welcome to ATM.

[WilDun]

Thanks for all the friendly replies - any others will be welcome.

[Smashinz2002]

Wildun, I'm not sure of the exact differences between powervalves on two-strokes these days. I have a KX500 which has the KIPS powervalve and it has a mechanism that adjusts the exhaust port opening depending on rpm.
The effect is to give the two-stroke engine an extremely wide power spread. For example, my 500 power spread is extremely wide, thanks to the powervalve. There is a huge amount of low-rpm power and torque right off idle, which builds smoothly (but very quickly) thoughout the mid-range and on into high rpms. There is really no so-called two-stroke "HIT" to it, unless you call the instant power right off idle a "hit".
Instead, with the powervalve, the bike's power is spread very evenly across the range.
The overall feel is that a bike with a powervalve is more tractable, easier to ride, and in general gives the rider more confidence to ride faster.

[chris99]

I know its not a bike but i had a 98 crg shifter cart with a 98 yz125 and the thing was a wild ride. I had some troubble with it falling on its face through cornering and hard excelleration. after a lot of troubbleshooting i found that it was the pin that holds the powervalve had fallen out so it was radeling open and shut at will causing the problem. some of the local cart gurus told me to eliminate the power valves all together to make the cart less snappy when you hit the throddle and less likely to want to spin out in corners under excelleration. I know its not mx but thought this experience might relate a little

[WilDun]

Seems that the power valves have now become something of a necessity to make high performance two strokes a little more user friendly, (at the expense of simplicity).

I used to road race a 250cc Suzuki twin a long time ago, and I remember that when I tweaked it by working on the ports, it used to bog down till it reached 7000 rpm, and then all hell broke loose, and the front wheel always wanted to reach for the sky! - a very difficult machine to master.

At the moment I have an RM 125 engine ( approx 1990 I think), and I've just acquired a pair of Suzuki RG 250 barrels with power valves, just to study.

I don't know if the exhaust chambers need to be different from those used on non power valve types.

Doesn't matter to me what the engine is in, I'm mainly interested in the engine.
As I said, I'm not too fit at the moment, so I have taken to flying model aircraft, and I'm trying to take a lead from Bikes and Karts, and play with the engines by getting lots of well proven info from these areas ( which is way in advance of the aircraft engines), - only trouble is, those people are a bit one eyed about discussing any improvements gleaned from bike sites.
etc. :
I guess, the bike and kart boys are a bit more willing to compare notes than that lot.