Power valve/CDI/Servo issue

  • Hi all,

    Wondering if anybody could shed some light on to what may be the cause of a problem ive been having. I’ve had this intermittent fault happen occasionaly before where when i turn my bike on i hear the servo operate correctly with opening and closing the port yet when i start the bike its almost like the port is open slightly therefore making it really boggy when pulling off. Also feels like i have 2 power bands almost with a burst of power after the boggyness on pull off and then the actually band where the pv opens after a flat spot. I can tell straight away after start up if its started in this mode yet usually all i do is turn it off and on again and its back to normal. Well today that wasnt the case and now its totally stuck this way along with once actually getting into the band its coughing and spluttering. Ive tried disconnecting and reconnecting the servo connector, tried disconnecting battery just incase somehow that reset it. servo seems to still open and close fine so i’d say thats not at fault. Adjustment of the pully cables is fine as it was going back to normal usually when this happened. Would i be right in saying its likely the cdi? Any help would be massivly apreciated.

    Thanks in advance,


  • Unfortunately, it'll be the CDI.

    Either way, the bike should not be boggy, it will lack the instant grunt, but should be perfectly rideable.

    There almost sounds like two separate issues here.

    I used to pin my servo open, just for the grins it would give me. Perfectly rideable like that.

  • @calum yeah im inclined to agree with you, just seem very strange that it was all to happen together. Throttle’s feeling nowhere near as responsive as normal until about 4k. Unless maybe lets say the servo has decided it thinks where it Is when the engine starts is actually shut but actually its slightly open more than norm. Then when it reaches the band it opens the valve that extra little bit too much which in turn just floods the engine with far too much which explains the coughing and spluttering. So its more than likely the cdi at fault then sending wrong messages to the servo? Any ideas of things to check before going out and getting a new cdi unit to eliminate any other possibilties?

  • @caldt125 The valve does not control fuelling mate. It won't flood the engine.

    The problem you're describing doesn't sound like faulty powervalve.

    It's a two stroke, there is no performance below 6K and you shouldn't really be riding it below that threshold.

    Pin the valve to the open position, disconnect the valve and take it for a blast.

    It should pick up at 6K and pull hard to the red line.

    If that happens then I'd be happy to say it's just the valve misbehaving.

  • @calum yeah i never normally ride it that low in the rev range mate was just saying today i had to as i was stuck 45 miles away from home with a bike that wasnt very happy atall when i got even anywhere near close to the pv opening 😂. Not too sure whats going on with it tbf. Riding it with the vavle constantly pinned open doesnt really interests me though as i like the low down grunt aswell as the top end. It had i felt a perfect contrast between the two previously, So what would you suggest i do next then? 🙄 im clueless otherthan to just switch the cdi and hope for the best

  • @caldt125 Literally what I just said.

    Pin the valve and ride it.

    if past 6K RPM all the problems go away, then I'll be happy to say valve.

    But your description sounds more like worn engine.

    So to convince me, I'd like to see the above being done.

  • @calum Alright then i’ll give that a go. Cheers for your help mate, much appreciated 👍🏼

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  • This issue I found to be a break in the wire that you ground from the cdi when derestricting the bike. went completely back to normal once I reterminated the connection.

    sorry for the late update on this, better late than never though haha could help someone in the future with a similar issue

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