I had heard of this and so knew what needed to be cleaned.

To do this you need to remove the starter motor from the bike. 

To do that you need to unbolt the air-box:

Accessing/removing the Starter-motor:

Loosen the rubber manifolds between the carbs and the air-box.  Removing the left side manifolds altogether will improve your access.  The air-box is held in place by a metal bracket that is, in turn, bolted to the engine/gearbox casings in two places. 

The first is one of the starter motor bolts and is loosened with a 8mm Allen wrench or socket.  For the wrench, the long arm is needed to reach the bolt and hence some sort of lever is needed on the short arm in order to loosen the bolt. If a socket is used, some extension arm in the region of 5 cm/2 inches will be needed.  Personally, I used the socket.

The second bolt also retains the clutch cable-tensioning bracket and is a 13mm nut. This can be reached with a spanner, just, but a deep reaching socket and the same 5 cm extension bar work well for me.

You don’t have to remove the air-box, but doing so will make life that bit easier and is not a major task once it has been unbolted.

Once the air-box is more or less out of the way you can turn your attention to the starter motor.  In order to save your casings from weld marks, and your nervous system from surprises, disconnect the negative cable from the battery.  Then unbolt the battery cable from solenoid on the starter and remove it (the cable) entirely from the bike, or it will just dangle in the way…  Also do not forget to disconnect the single blade connector from the solenoid cap. 

At this point, you might want to at least loosen the bolt that retains the white solenoid cable.  It’s easier than trying to do so holding the starter motor in your hand.

By now the only thing keeping the starter attached to the bike is another 8mm Allen bolt, located under the starter toward the outside.  This is easier to reach, but here I used a long extension bar to preserve my knuckles should the bolt suddenly jump loose.

When you remove the starter some “oval” shaped metal shims will come away too.  These should be retained for reassembly.  Don’t bend them…

Now your starter motor is off.

Dismantling the solenoid:

The starter motor is comprised of two parts, the motor itself and the solenoid that branches off to one side.  The solenoid is what we will focus on.  Fully disconnect the white cable, if not done already.  Loosen the two slotted screws recessed in the red solenoid cap.  One may have been dabbed in red paint.  No need to remove them entirely yet. 

Before the next stage, look at the starter/solenoid assembly head on so you are looking down at the top of the red solenoid cap.  Take a photo, draw a diagram or make a mental note of how the solenoid is orientated, so that upon reassembly you can ensure that all is back in the right place, especially that the single blade connector is orientated in the correct direction.

Now use a 8mm spanner and a screwdriver to undo the coupling bolts midway down the solenoid body.  This means that the solenoid can be removed from the starter.  Once undone, the solenoid will come away.  Dismantle with care as a spring is located inside and this will fall out.  Put it to one side, and ensure that the metal cylinder that resides in the starter motor (which the spring is recessed in) does not fall out as it is hooked to a lever that slides the starter motor back and forward when being operated.

Cleaning the Solenoid:

Now you can return to the solenoid: Undo the two loosened cap screws and place them to one side, taking care not to lose the washers.  With gentle pressure, you will feel the solenoid cap move.  You will feel one section is not moving as freely as the rest.  Under the cap a small white wire is soldered to the cap, so DO NOT PRISE THE CAP OFF COMPLETELY.  In fact, use as little pressure as possible to ease one side of the solenoid away from the body so that you have between 5-7 mm of access, whilst putting the white wire under as little pressure as possible.  Here a pen-touch/head torch is useful.

However, if you have access to a decent soldering-iron and are competent with using it you can melt the solder that holds the above-mentioned wire (it resides in the blob of solder that sits adjacent to the thick, white, negative heavy duty cable that runs between the solenoid and the starter motor) and this way the cap will come clean away from the solenoid to give you free and easy access to the components: based on information posted by Russian Iron member, Ron Cichowski.

Under the cap you will see (just) two discs recessed in the cap itself (these are the contact terminals of the two threaded bolts the power cables are bolted to: called cap-discs from now on).  Then, attached to the solenoid yet mobile, there is a large copper disc that has a spring in its centre pushing against the cap.  This disc also has a small section cut out of its circumference on one side.  This disc is what bridges the gap between the two cap-discs mentioned above, when the starter button is pushed, allowing the current to reach the starter motor and crank the engine.

The disc can be tilted lightly, this way and that, as well as rotated about it’s central axis.  First I used a flat, but wide, precision file that I gently rubbed over the surface of the large rotating disc.  A nail file would also do the job. 

Rotate the disc, sand a bit, rotate some more, sand etc.  Finally, stop when the cut section of the disc was back where it has started.  You should just see a fresh surface of shiny copper, using the torch.  When you stop ensure that the cut section is not directly below one of the cap-discs as it may result in a bad contact when operating the starter. 

To clean the cap discs, I put a small filing bit (as used with “Dremels” and the like) into my cordless screwdriver and gently removed any oxidation until fresh shiny copper was visible.  This is fiddly but not too bad, however, a head torch is definitely advisable.  A hand held file would be far trickier.  Throughout the sanding phase, be sure not to over-stretch or nick the white soldered wire in the cap.  If you go down the de-soldering route, then your choice of abrasive is much greater!

Once this is done, you may want to get a cotton bud, put a dollop of silicon grease on the end and smeared some grease over the cap-discs, and over the surface of the sprung disc (keeping the cut where it was supposed to be). 

Screw the red cap back down. (If you opted to melt the solder on this wire, remember to re-solder it before completing the rebuild and mounting on the bike.) At this stage, I then found a suitable rod (like a drift), balanced the solenoid on it so that the rod that comes out for the back of the large disc could be pushed upward, against the cap spring, thus making contact between the large disc and two cap-discs.  Whilst doing this (quite fiddly, now), I used a multi-meter to measure resistance to see that the grease was not too thick and that my cleaning had done the job.  This process is optional, but better to know now if something has been damaged, than when you try the starter button…

I also measured resistance to ensure that my work had not damaged the link between the exterior solder of the white wire (next to the bolt the white cable is bolted to) and the metal body of the solenoid. 

This done, re-bolt the solenoid to the rest of the starter motor, taking care to orientate it as remembered/picture.  This first involves putting the loose spring back in the large metal cylinder recess on the starter motor side and seating the open end of the spring over the rod coming out of the back of the solenoid (connected to the large copper disc).  You may want to also put a little silicone grease over the mating surfaces to limit the ingress of moisture later on. 

Once done, I used silicone sealant to seal the join between the red cap and the solenoid body.  I have no idea if there will be any ill effects of doing this, but for me there is precious little seal between the red cap and metal body and moisture seems the likely culprit for the corrosion I had had to clean, so time will tell if this is a mistake.  Therefore, do this using your own judgement only.

Reassembly to the bike:

The starter motor is now ready for reattachment to the bike, taking care not to forget the use the metal shims, attached the power cable first to the starter and later to the battery, connecting the single blade connector, tightening all bolts nicely and giving everything a good coat of silicone grease to prevent corrosion. 

I, personally, used some PVC water piping of an adequate diameter to for a cowl around the cap electrode as corrosion had already cost me one power cable and a week of cold morning kick-starts.   

Once back in place the air-box can be re-mounted, clutch cable re-secured, all rubber manifolds reattached and made airtight. Finally the positive can be reattached to the battery.