125-200cc How the Power Valve works (sounds stupid)

Hi Guys,

Wondering if anyone can detail how the power valve actually behaves?
Differences between CR/WR power valve setups?

Thing is, I have a CR barrel on a WR engine with the electronic power valve.

This is my project bike so I'm looking to possibly build my own PV controller. The motor on this has a potentiometer to sense how far open or closed the valve is but otherwise its a basic 12V motor that I could easily work with. Right now it's opening very late I have to really gun it up through the gears to have it open - try to accelerate hard at any other point and you just get to the point before the valve should open but it doesn't. The stock controller probably has a map that isn't working too well for me now and I've been having issues with the PV sometimes not opening at all.

Ideally I'd swap the left side engine casing for the mechanical PV type with the PV arm and cover but until then this is my plan. I'm pretty sure I could put an arduino setup together sensing RPM via an inductive pickup or maybe even just a open/close button on my handlebar...

What I really need to know: do the mechanical power valves snap open or slowly open with RPM?

Just looking to figure out if ill get better results opening and closing it myself.

This sounds like a cool project.

Both mechanical and servo driven power valves open progressively to give more usable power across rpms. Generally enduro type 2-strokes open sooner/faster whereas mx/sm setups are usually wrung out more so they open later/slower. Having your own controller for it would be handy you could have different 'tunes' for different types of riding.

On another note, have you tried adjusting the PV you have on the bike now?

Thanks for this, sounds about right to what I was assuming. Yeah I've messed around all day, all I can change is the tension on the pulley wires at the valve end to ensure I have the valve fully closing and fully opening (I can slightly vary the adjustment to have the valve already slightly open when it should be closed or not open fully when it should)

CR and WR have the same power valves set up and actuation characteristics

the servo driven set up has probably a detuned curve as it is a form of control to keep the power down in the bike
SM and WRE are build to meet certain classes in some country (learner bike)

playing a bit with the servo unit can probably push a few more ponies out

Robert-Jan

Hello Harley,
i have a lot of these engines and have been messing with them for years my WRE was dyno'd at 23BHP, not that it means much!. i'd go back to basics if i were you and get the set up you have working first before adjusting it. i'm not being an a**hole but can you try and write down exactly what you have as it makes things easier. i take it you mean "WRE/SM" engine not "WR" as that has mechanical PV? also you must mean the "right" hand side engine case, not the left? i would remove the head and check that the valve is closed when bike is off, then when you turn on the ignition the valve should cycle fully open then close again. there are markers on the valve pulley that need to line up and the cables cannot be to tight, has this all been done? is the battery in good condition?

I have the wre too, 2005, dep system, rejetted, put in a mitaka piston riken ring, cr cylinder head, no idea about bhp but it must be way over the 15 or so it came with, I read about people claiming their rs/ mito's making over 30 hp which seems way too much, what set up has your wre got? I guessed I had 25 at the rear wheel maybe 27/28 at the crank

Hello gaz, guessing bhp is a dangerous game! When I got mine dyno'd it was Gibsons two stroke day, and they had a prize for whoever got close to guessing what there bike would do. Not many winners! I would say if you're running the original delorto carb, then you won't be able to get enough air/ fuel in to get up into the 20's . Mitos rs may make upper 20's but most of there owners talk rubbish about how they got 120mph out of it. Wr only puts out 28bhp from memory. Cr 30 something? From memory I was running 38mm carb, full dep/fmf and jetted properly. Mine did 23, then yam wr200 did 24 straight after.

that's ruined my evening, I kept bragging to my dad how my bike had 200 plus bhp per tonne! oh well. I've had my fair share of top speed claims, the funniest was me at 16, believing my aprilia rx50 would go 80 miles an hour! Dad rode alongside on zzr600 and said I was going 55 tucked down :{ I've had people on mito's and rs's saying they'll do 110/120, I don't believe it, my rs 125 was derestricted and indicated 103 max, so probably more like 93, and that was at 13000 rpm so even with longer geared sprockets I can't see where 120 would come from