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Z50m tune up

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  • Z50m tune up

    Hey guys,

    I have a z50m which was always really hard to start. Compression felt a little low and came to 105psi when tested so it might be a bit more taking into account the length of the guage hose.

    My original plan was to tear down the motor, measure everything and replace what was needed. Just before pulling the motor out I decided to just try and start the bike.

    After a lot of playing around I couldn't get the bike to start but I know I had gotten it to start before so something wasn't right.

    I thought I would start with the carb. Opening the air filter housing revealed no filter at all. An order to Jaimie had one on the way. Maybe it being too lean was making it hard to start even with the choke. After installing the filter no real difference occurred.

    Off the carb comes. I spotted a few tiny granules in the clear fuel hose so I disconnected it and flushed them out. When I took the carb off I pulled out both Jets. The emulsion tube looked nice and clean but the pilot jet I couldn't see any light.

    So carefully removing the blockage and a little soak in degreaser they were back in. I also took a look at the float level while I was at it.

    The float height measured 16mm but the manual spec is 18mm. I carefully adjusted it and checked a couple of times.

    With the carb now reassembled and installed into the bike I rechecked the pilot screw putting it at 1-1/4 turns out.

    Ignition switch on, fuel on, two kicks and it comes to life. Brilliant!!

    The bike was revving quite high so I thought it a good opportunity to use a pulse tacho that I purchased off eBay. You can put it to the ignition lead and it tells you the rpm. 3100ish was the reading.

    Back to the manual calls for 1500 +-100rpm. Winding down the slide adjusting screw on the carb let the bike sit nicely at 1500 without any fluctuations.

    Now at this point the best test you can do is a slow and fast roll on to see if there is any stutter or movement when it returns to idle. Both tests went very well leading to one happy backyard mechanic.

    The weekend presented a lot of rain so I didn't get to go for a little test ride so those results will have to wait.

    Hope this info is helpful to someone. But it was nice to sort out a small problem and not have to start tearing down the motor in search of something bigger.
    Life is too short for cheap carbs...

  • #2
    good job Matty, while ya bike is warm and running adjust ya pilot screw half a turn or 1/4 turn and see if it runs faster or slower at idle, adjust it each way to find the fastest running position and its done. i always re tune when hot and find the fastest smoothest position...................... do not tune a 2 stroke the same or it will seize.

    don't know about anyone else but i think fuel is crap today, 30 years ago you could still start a car or bike after months of storage and have little to no problems.

    You have two parts of brain, 'left' and 'right'. In the left side, there's nothing right. In the right side, there's nothing left.

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    • #3
      Yeah will do. I'm looking forward to taking it for a little ride so I'll adjust the mix when it's nice and warm.
      Life is too short for cheap carbs...

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      • #4
        Pix of the bike or it didn't happen!

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