66cc timing help? tips

Discussion in 'General Questions' started by jakeriley1616, Apr 9, 2011.

  1. jakeriley1616

    jakeriley1616 New Member

    hello i have a 66cc(80) bike. i am wondering how to adjust the timing, obviously there is no way to use a timing light on this thing is there anybody out there that has played around with their timing?????? thanks

  2. PedOpt

    PedOpt New Member

    If the engine is a 2 stroke, there's nothing you can do about the timing. Single cylinder 2 stroke engines work with the intake cut at one location and the exhaust cut in another. As the piston moves upwards it ignites thus forcing downward action of the piston. As the piston moves downwards, it opens the intake port drawing in the next fuel charge and at the same time it's also exhausting the waste charge. The piston itself acts as the "valve". Both intake and exhaust. In 4 stroke engines regardless of the number of cylinders have a camshaft in which when spun in sync with the piston(s) which lifts the intake and the exhaust valves. It's this "timing" in which you can adjust. If you have the 2 stroke engine, try this once, undo you spark source from the engine. Then, undo the four head bolt nuts and take the head off, as well you can then slide the cylinder head off the piston. You'll see the two ports in relation to the exhaust pipe and the carb.
  3. GearNut

    GearNut Active Member

    The ignition timing can be adjusted with an offset key.
    Retard the ignition timing for more high RPM speed at the cost of loosing low RPM power.
    Advance the ignition timing for more low rpm power at the cost of loosing high rpm speed.
    One can go too far and loose any benefit of adjusting the timing, but a typical offset key only advances or retards the timing by 1/2 a key width. Any thinner than that and the key will be too weak to be of any use.
    You can make your own by filing the stock key.
  4. What is the stock key?
    What is the offset key?
    How do u adjust the ignition timing?
    Please dumb down the explanation I am in high school and am still new at all these mechanical stuff.
  5. Steve Best

    Steve Best Active Member

    First off, you have done well to buy one of these motors as your education into motorsports!
    Cheaper and easier to work on than a scooter or motorbike. Go slow and we will keep you advised true.
    Do any mods ONE AT A TIME so if it doesn't work, you know what is wrong.
    Also, don't go crazy with your mods, go easy and gradually increase whatever you do. More is not always bettter.
    Your ignition is fine as it comes, experiment as you like but too much timing advance can burn up a piston.

    Here is a stock Woodruff key:

    Here is how they cut its slot and how it fits:

    Here is an offset key, they can have different amounts of offset:
    Moderately hard to make unless you have great handskills with hacksaw, vise and file.
    On tapered shafts they are generally for location only but their strength is more important on these straight shaft motors.

    I generally find with work on combustion chamber work I can raise compression a bit and actually retard the timing because of the faster burn speed and yet still gain great gobs of low end torque. My advice is to forget the ignition timing, leave it stock and work on your head first, ports next, and always one step at a time.

    Buy spare gaskets and maybe a spare piston/cyl/head to experiment on so you can always go back to stock if your mod (only ONE MOD, right?) doesn't work out. Learn about measuring your squish with lead solder. Buy a small torque wrench so you can tighten the bolts right. Find a hill and measure your power progress after each mod with how fast or how far you can go up it. These motors are capable of double the hp without buying a single "performance" part. Read some of my old posts.

    Steve Best
    Last edited: Oct 10, 2016
    Holly likes this.
  6. jaguar

    jaguar Well-Known Member

    or just buy an adjustable CDI and be done with the stock crap
  7. KCvale

    KCvale Motorized Bicycle Vendor

    Or just get an Expansion Chamber exhaust and drop in an NGK 5944 (BPR7HIX) Iridium spark in and forget about timing.