ktm dual ignition

[Reckless]

can someone explain how this tunable power valve works?

in theory the CR powervalve & ignition could be very tunable if someone were to dick around with it, seeing as it uses the throttle position to adjust the ignition map and power valve, in theory you could have some sort of variable resistor that works in conjunction with the tps sensor to give gentle maps / valving thru to the full on aggressive glory

I'm going to keep this really simple and short, in so, leaving myself open to the usual KB Knit picking and fault finding but here goes.

The 2 stroke power valve closes off the exhaust port they basically work by spring pressure. On all my kart engines (Yamaha, Kawasaki & Cagiva) there is a shaft driven off the clutch basket (Ktm may do it differnetly but the principle will be the same). There are weights on this shaft as it spins faster the weights put pressure on a spring which is attached to a lever which opens the power valve. Faster the engine speed the more the port is opened. Little bit like strangling performance down low. Pretty simple but very effective mechanical activation system.
So different springs open the power valve at a different rate and also adjustment on the activation means it opens later or sooner. In our Karts we used to machine the clutch basket off the drive cog (so no clutch at all draining power) and re spring the power valve mechanism so it opened faster. You could re spring the power valve mechanism with your CR 250 to achieve the same thing. Its just Ktm in their wisdom have decided to design a system that has replaceable springs of different tensions (3 supplied with every new bike) and an adjustment system that allows us to decide when we want the HIT as well.
Combine this with different electronic mapping in the ignition and you basically have what we are talking about above.

just but a fuckin 450 4 stroke problem solved

Again combine the above with different pipe designs and fly wheel weights and I repeat what I've always said you can do anything with a 2smoker the japs just don't want too as the factories and dealers make much more money out of 4 stroke valve tune ups and replacments. In saying the above I'm not sure if you could make a 2smoker as linear in power delivery as a 4 stroke but they could come very close I reckon. My 200 tractors from down low better than my CR did. Thank goodness for the Euro's keeping strokes alive and developing!!

[B0000M]

You could re spring the power valve mechanism with your CR 250 to achieve the same thing.

the bulk of your statement is true. except that the 03 (could be 04) and newer CR250 has a electronic solenoid which is operates 2 cables which operates the powervalve or 'rc valve' as they called it. so the whole power valve is controlled by electronics, hence my idea

[Reckless]

Ah yes B0000M the bulk of my experience is with earlier engines so I have no knowledge of your model. Looks like that Ktm have stuck with the spring pressure system. It seems that there's much more flexibility for Ktm in the older mechanical type system. In their wisdom Ktm may have decided if it ain't broke don't change it. Looking at the manual it looks very similar to what I've seen in past engines on my 200.

Hey rick I never bother with turning the power-valve nut I just change the springs around , did you get the three springs with it?

In picking up the manual to have a look at how the power-valve activation looks like the 200 doesn't have changeable springs like the 250/300 does. I thought you had discovered a new feature of the 08 vs the 03. The changing springs section only is for the 250/300 bikes. I'll have to investigate further I've only had the bike a few weeks. But turning the power valve nut makes a huge difference on its own. I think the 200 engine has been a little winner for a few years and the haven't touched it I'm thinking the 03 and 08 engines are the same. Somehow though, they've made the power delivery softer it certainly climbs much better than the 03 does could well be flywheel weight and powervalve spring settings I suppose. Who knows I'm not that good LOL!!!

[camchain]

I think the other reason power valves work is you're raising/lowering port timing. My guess is KTM went with a different PV design for the smaller engine as it's a bit more manic so more subtle adjustments required(?)

KTM are strange buggers for adding the dual curve ignition and then keeping it secret by not adding a switch. Even the dealer reckoned mine didn't have it, so I did a double check and found it.

BTW, anyone know where you can get the proper dirt bike clear/soft waterproof electrical connection sleeves? Re-wiring mine to be more like the much simpler XC wiring so would like to keep things tidy and crud free.

[warewolf]

In picking up the manual to have a look at how the power-valve activation looks like the 200 doesn't have changeable springs like the 250/300 does. I thought you had discovered a new feature of the 08 vs the 03. The changing springs section only is for the 250/300 bikes.

AFAIK you are correct - I didn't think the '08 was different otherwise there'd be lots of talk about it. The 125/200 engine has only spring preload adjustment whereas the 250/300 engine has the 3 spring rates. They are two distinct 'families' of engines.