The Mordern Bajaj Chetak Rides One
Per Al K:

"When tightening the nut for the rear wheel you tighten it to around 90 ft./lbs. torque. In this case, you are NOT putting any load on the bearings. you are tightened the hub and inner race against a shoulder on the main shaft. The clearance of the main bearing on the rear wheel main shaft of the Bajaj engine is fixed. No matter how loose or tight you make the nut, the bearing clearance will remain the same."   

This is critical as the rear hub nut holds the rear wheel onto the splined drive shaft.  If this hub nut comes loose, there is a good chance that you will strip the drive shaft splines necessitating a major engine repair.  2003 and later models had a slightly larger drive shaft with slightly more robust splines.  This was one of the few changes made after the modern Chetak hit the American roadways, the American riders spent more time at higher speeds placing higher forces on this splined shaft.  The other major change involved a larger CDI as the American riders had the mandatory "head-light on" federal requirement that the 2002 CDI could not keep up with.
Only fill the tank to the first ring at the bottom of the filler neck. Look inside you will see that between the bottom ring and the top ring, there is a vent to the emissions system. Ff you overfill, the excess gas goes down that tube to the emission can that is filled with charcoal and once that gets wet it cuts off the air to the tank causing a lock the gas in the tank wont move without air. This causes sputtering, hesitation and rough running; even quitting.

In the early days, riders with this problem resorted to drilling holes in the gas cap to prevent this vacuum lock, but most found the emissions hose easy to disconnect to relieve the lock and learned to keep the gas level below the ring. 

This is a procedure that you should read entirely before lifting the first wrench.  To replace the lever you will need to deal with connections at the lever end and at the engine end, so it pays to know in advance what you will encounter.

To replace the clutch lever, you need to remove the single nut from the bottom of the headset on the clutch lever side. Then, using a flat-head screwdriver, unscrew the threaded bolt from the bottom of the headset. You now have to disconnect the cable from the lever. You will need to get down by the enigne and loosen the pinch bolt so you can slide enough cable up to give you spare cable at the lever to disconnect the cable from the lever. Then, be careful as you remove the lever as there are two small washers that will come out with it - one on top and one on the bottom. Save these, as you'll need them! 

This is probably also a good time to replace the cable.  Inspect the cable outer to make sure it's in good shape. Lubricate the new clutch cable using a lube of your preference - grease or chainsaw chain oil  etc (each has proponents and detractors). Thread in your new clutch cable from the headset. Don't connect the cable to anything just yet. 

Now install your new clutch lever. It can be tricky with those little washers, but be persistent and you'll get it. Grease up the clutch lever on both sides and in the bolt hole. Put a washer on each side of the clutch lever and insert the threaded bolt through the bottom of the headset, through the washers and clutch lever, and into the threaded part of the headset. Be very careful with threading the bolt in because it is super easy to strip the threads in the headset (which is a difficult repair). Once you've got the bolt threaded in correctly, thread on the nut and tighten it to the point where it is nice and snug but you can still operate the clutch lever with very little resistance. 

Now put the clutch cable into the retaining hole on the clutch lever. Grease this area well as it sees a lot of movement which causes parts to rub against each other and wear. Pull on the clutch lever from the engine side of the frame and make sure things are working well. Thread the cable properly through the adjuster and clutch actuator arm on the engine side. Attach the pinch bolt behind the clutch actuator arm and adjust the clutch cable to your preference. 

The Modern Bajaj Chetak Rides On The Modern Bajaj Chetak Rides On