Yamaha Aerox always running lean (Help)

Discussion in 'General Tuning' started by Karmafield, Apr 5, 2021.

  1. Karmafield

    Karmafield Member

    Messages:
    69
    Hello.

    My friend gave me his scooter to fix.
    It's a stock 2 stroke Minarelli Yamaha Aerox with a Gianelli Extra exhaust.

    He crashed it, drove it to a storage not so far from the crash, left it there, and since then it stopped running for 2 years (couldn't start it after the crash).
    But that all changed when he gave it to me. Turns out the vacuum tap was clogged, so I cleaned it. So easy, right?
    Well, this sadly wasn't the case for me, since it bogged and ran really lean.
    I thought maybe the jets are clogged, so I cleaned the carb. Nothing.
    It was really hard to start, so I changed the piston with the gaskets. Better, but still bogging (The piston had really low compression and had stuck rings).
    I changed the carburetor from the WEBEN 12mm to a Dellorto 17.5 since I had main jets for it.
    Clip position in the middle, 108 main jet, idles perfectly, on half throttle it runs rich, but on full throttle it runs soooooo lean that it isn't normal.

    So I asked my friend: "Why does it bog? How did you drive your scooter lean and bogging for so many years?"
    To which he replied: "It just started doing that, I don't know"

    Could this be a symptom of bad crank seals? It sure isn't normal that the main jet for a stock setup is 108 and still running lean. I don't know what else could there be wrong.
    Please help.
     
  2. Stevep

    Stevep Well-Known Member

    Messages:
    5,895
    Is it the 50 or 100cc version?
    I have a more or less stock Aerox 100. I've just put a new 17.5mm carb on it. It came with a 90 jet installed which was hugely oversize for it so I down jetted to a 70.
    I also have a (slightly) strangled open air filter on it so it picks up really well. Haven't tried it on the road as yet because it isn't finished, but up my driveway it feels like it'll pull really well.

    You'll be able to see if the crank seals have gone because they will weep oil past them behind the variator and stator.

    To be straight, you shouldn't even be thinking about running that at full throttle yet, you have to run the cylinder in for a good 100 miles with just a piston change, or 300 miles with a piston and barrel change, before you start to get the proper performance out of it.

    Raise the slide needle to the highest point, mixture screw about 2 1/2 turns out from fully home.

    Q: Manual or electric choke???

    If it's electric, test it, might not be working. But also test the plug connection to it. Maybe the resistor has packed up so it's not operating the choke.
    Also, is it the standard air filter?
     

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