When working on a 2 stroke motorcycle with a run on condition or a high idle, the problem can occasionally be tracked to a leaking LH crank seal which is essentially a vacuum leak allowing unmetered and unfiltered air into the engine which can ruin a perfectly good piston and cylinder (among other parts) in no time.
On the bikes which won't start at all, or are experiencing electrical issues such as intermittent open circuits (no continuity), removal of the flywheel will allow you a close visual inspection of the stator and any lighting, or exciter coil(s) as these occasionally develop loose connections at the solder joints resulting in intermittent misfires, lights that are dim or have no lighting power at all, or a motorcycle that loses spark completely.
Be Sure You Check the LH Crank Bearing for Wear
Once you're determined to remove the flywheel, before actually removing the flywheel it's wise to check the left crank bearing for any wear, as worn crank bearings will require replacement and checking these is usually easier with the flywheel installed as it will allow you more to grasp than only the end of the crank.
How to Remove the Flywheel
The flywheel is pressed to the crank via the center nut, with a tapered fit on a keyed shaft, and removal of the flywheel from the crankshaft does require a special flywheel puller, as no other type of pullers are suitable, and attempting to use anything other than a flywheel puller is sure to result in a damaged flywheel and / or crankshaft.
- Begin by using an impact wrench, or a flywheel holding tool with a socket and ratchet, then loosen the nut in the center of the crank and remove the nut and washer.
If There's A Flywheel Weight Installed, Remove It Before Continuing.
- With the nut and washer removed, ensure that the center bolt of the puller is backed out, then thread a flywheel puller into the flywheel (Likely LH Thread) until bottomed.
- With the flywheel puller securely threaded into the flywheel, hold the outer part of the puller so it doesn't move, then thread the center bolt in against the nose of the crankshaft until tight.
- With the flywheel puller threaded securely into the flywheel and the center bolt in contact with the crankshaft, hold the outer flange of the puller and tighten the center bolt with moderate force. (~50 - 80 lb -ft of torque if necessary)
- If the flywheel does not come off upon tightening of the puller, using a brass hammer, strike the end of the puller using a sharp blow focused directly on the end of the puller, then re-tighten the puller and the flywheel should "Pop" and come off.
Once the flywheel is removed, the stator plate, along with the coil(s) and pickup(s) and all of their mounting hardware will be visible, enabling you to remove the fasteners securing the entire stator plate to the crankcase, ultimately allowing unrestricted access to the electronics and left crank seal.