TOP END FLAT SPOT



  • Just a random enquiry really....

    I have recently rebuilt the top end of my DT and alos stripped the carb and rebuilt it along with new plug, I also stripped the power valve and set it up precise and what i image would be the "standard" position.
    Ensureing the plastic valve clip thingy lines up with the hole in the casing and ensuring the valve is flush inside the manifold when the ignition is off.

    I have noticed that the valve kicks in fine through the gears but the high revs (7k +) it is incredibly flat and no pull what so ever.

    Any idea what it could be.?

    Thanks in advance.



  • What year is your bike mate? Has it been derestricted?



  • Sounds like the valve hasn't been setup properly.

    It's not a case of making the powervalve flush with the engine off. It's making the exhaust flush when the engine is at maximum RPM's, or 7K plus.

    It sounds to me like the valve is shut at 7K hence why it's not pulling.

    This could be due to various reasons. Faulty Servo/ CDI or flat battery.

    From your explanation it sounds like you may have not set it up correctly, or rather this is the cheapest assumption to make.

    The idea is not to set it up when the ignition is off, but rather let the valve do it's full cleaning cycle.

    It goes something similar to this.

    When the ignition is OFF the valve is SHUT.

    When the engine is at peak RPM the valve SHOULD be open.

    When the bike has been running and the ignition is switch OFF THEN ON the valve will perform a cleaning cycle.

    The valve will go FROM CLOSED TO OPEN BACK TO CLOSED BACK TO OPEN.

    Then if you switch it on and off again it does a shorter cycle of just CLOSED to OPEN to CLOSED.

    Something like that.

    You will hear the powervalve do an extra cycle only after the engine has been running.

    It's once it's completed this cycle that the CDI thinks the valve is open. This is how you should then rectify this.

    I suspect you didn't let the cleaning cycle operate before setting the valve, and have in fact set the valve to the incorrect position.

    Quick way to check is simply to turn the ignition on and off twice then ensure the valve is flush with the port.

    If it is, then sweet we will check to see if it's a restricted CDI,



  • Could be the jetting aswell, both rich and lean conditions will do that.

    Also, minor changes in floatheight makes big changes.



  • @Jens-Eskildsen It will cut out if the float height is incorrect as it will run out of fuel.

    Yeah there are loads of factors why the top end is flat, perhaps I made a mistake in assuming the bike was standard.

    If you don't know what you are doing, then my advice would be to get the bike exactly like it was from the factory, then we can help.



  • Hello,

    Have you checked if the powervalve is really fully open? When the servo is in the opening position?
    By removing the exhaust and feel/see it.

    Just pointing it out as you can mound that plastic thing two ways
    alt text
    http://www.tzr3ma.com/tzr125-4dl-restricted-ypvs.html

    If you already know this, forget i have written this



  • Hmmmm, thanks for the replies.

    The bike is a 2003.

    I will take a look at the power valve tomorrow and see its functions to see if it is linned up correctly or not.

    The power valve certainly does kick in nicely when going up through the revs but fats out after 7k.

    The bike is not standard, I do not know what mods have been performed other than the after market exhaust system.

    It maybe jetted, It may not.

    Perhaps it has a restricted CDI....

    I bought the bike recently as a none runner and so far ive just rebuilt the top end with a new plug, had the carb apart and rebuilt, had the pawer valve out, cleaned and reassembled and stripped and cleaned all the obvious earthing points and also a new battery.



  • @dazzagtir my powervalve kicks in at around 7k



  • @Calum You can have to big a fuelheight, and the engine will be rich. This is possible even without the carb overflooding. if its really excessive, then the bike will spit fuel out the overflow when its on its sidestand. The same goes the other way, it can very well be lean, without running totally out of fuel. When fuellevel is lower than its supposed to, more air can rush by. As I said, af few milimeters makes a lot of difference.

    I had this exact problem when i bought mine used. It was only running witch choke on, so the PO assumed it was very lean, and richened it by altering the fuellevel. What was wrong was that all jets were partially blocked, so the bike almost lived entirely of the choke circuit. It didnt run that well 😀

    As to the OP, set everything to stock, so you dont have too amny things fooling you. It could very well be a combination of things. Atleast this way you ran rule out a lof of stuff.


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