I heartily concur with Brother Blasphemous: Get yourself a proper copy of Snidal's superb manual
right here.
Next, it sounds like you'll need some tools. Check out
this great 4-drawer 105-piece set over at Harbor Freight for under $40. They may not be the shining epitome of the toolmaker's craft, but they
ARE plenty "good enough" and handy as hell. Avoid the new 130-piece set. Made by some other Chinese factory, its quality is currently quite poor in comparison to the 105-piece. Pro Tip: You'll always find a bunch of 20% Off and freebie-with-purchase coupons
right here to print out or call up on your phone, thanks to the good folks at the
Harbor Freight Coupon Database. I highly recommend getting the freebie
Digital Multimeter, if you don't have one already. There's a Harbor Freight near you in St. Paul at 9 SIGNAL HILLS CENTER, SAINT PAUL, MN 55118; Tel. 651-306-0555.
Get directions here. While you're in the joint anyhow, do yourself a favor and also grab a little bottle or three of something called
Threadlock No. 42. A drop of this blue goo on the threads of
every nut and bolt you henceforth tighten will really help keep those vibes from skittering them off and sending them "where the woodbine twineth". Keep one in the bike's tool pouch. They're very small. You might also want to grab a 3/8" drive torque wrench, an extra set of combination wrenches and some 3/8" sockets (you can never have enough sockets), as well as likely consumables such as
RTV gasket sealant and electrical tape. You won't find these any cheaper elsewhere. Bungee cords are always good too.
Now order a proper Barnett clutch cable from our hosts in Ft. Worth. Accept no substitutes, and certainly
DON'T get that piece-of-shit OEM Royal Enfield cable, which appears to be made from recycled cat food cans. My hunch from your description of "its adjuster midway through the cable" is that your current "gearbox problems" may well stem from one of those original craptastic cables breaking, being replaced by some "make-do" near equivalent, possibly some throttle cable (?) which could never
quite be adjusted properly, and hence your woes. With a bit of luck, fitting a proper Barnett cable properly may solve your problems without your having to dive into that scary gearbox. A quick overall diagnosis of the state of wear of your gearbox and any havoc possibly wrought by poor long term clutch adjustment might be gleaned from draining and examining its gear oil. Lots of metal particulate or (God help you) chunks and slivers of metal would indicate that the gearbox itself may need attention. But more likely is that all will be honey golden and sweet as pie once you mount and properly adjust that Barnett cable and refill your later model 4-speed box with SAE 90 straight GL-4 type gear lube (
NOT Gl-5 or "Gl-2 through GL-5"--If you see "GL-5" anywhere on the jug, best to just leave it on the shelf. If it's not in the automotive lubes section, look in the boating section for a straight GL-4 as used in outboards and outdrives, like Quicksilver, Mercury's fine house brand).
By the way, if that drained gear oil is pretty clean, transparent and sort of golden brown, and not milky or black and "sooty looking," then run it through a coffee filter once or twice, allow that to settle a week or so, and pour all but, say, the bottom inch or so of the filtered result into a tall capped jar with a little 1" or 2" wide paintbrush, and there's your free chainlube. A quick brush stroke along just the easily accessible lower run of the drivechain now and then when you come back from a run, and both the chain and sprockets WILL thank you with far longer life and extended periods between necessary drive chain slack adjustments.
Anyhow, best of luck! I'm really hoping your woes are just the result of poor adjustment. You'll get it sorted!