Dr. Watson: Holmes, I've noticed that the starter on your V-Strom occasionally cranks slowly.
Sherlock Holmes: Indeed, Watson. Because the problem is occasional, it isn't the switch or the battery, and unlikely to be the relay. Therefore, we'll look into the starter motor.
The starter motor is the Mitsuba SM-14 that is widely used on many small engines, although the ends might be unique to the V-Strom. Brushes and the brush holder assembly are widely available from small engine parts suppliers at good prices. The starter motor drives the engine through an overrunning clutch. It looks kind'a like a roller bearing where it rolls freely in one direction (when the engine is running) and locks in the other direction (so the starter can turn the engine over). This overrunning clutch is inside the engine case; it stays there when the starter motor is removed.
The motor is bolted to the bike by two mounting feet. Remove the two mounting bolts and the electrical cable, and expect the motor to be somewhat stuck into place by the o-ring oil seal on the left end (all left & right are the rider's left & right when seated on the bike). Wiggle it out or pry gently without breaking off a mounting foot. Take care removing the insulating rings from the power cable bolt. These rings need to go back on in the correct position and order to keep the power from shorting to ground.
Wipe out the mounting hole--no metal bits showed indicating excessive wear. I cleaned the motor exterior after it was out, then took it apart--note the marks on the exterior for correct alignment of the three parts of the housing.
--The left end had good shaft splines, the shaft was straight and not worn.
--The end cap had a good needle bearing and good internal oil seal.
--The armature windings are encapsulated in epoxy and looked good.
--The commutator was a good coffee-brown color with wear, no burned areas or pitting, and the mica insulators between the copper segments were still undercut.*
--The two thrust washers on each end of the shaft looked good.
--The brushes were good length with good spring tension. One possible cause for the intermittent slow cranking is a brush occasionally stuck in the brush holder due to a build up of carbon dust. I cleaned these well with electrical parts cleaner.
--The right end of the motor shaft showed a very small amount of bronze from the bushing plated on the steel shaft, and the bushing was dry. I think this was the main reason for the slow cranking--the dry bushing.
I cleaned everything with electrical parts cleaner, put a small dab of any good chassis & bearing grease in the bushing, very small dab on the thrust washers on the shaft, very small dab of grease on the oil seals, and put it back together matching the marks noted above. If it doesn't fit together just right, something inside isn't lined up--try again. Back in the bike with blue Loctite on the mounting bolt threads, attached the power cable, and it cranks great.
*The coffee-brown color of the copper commutator is good. It doesn't need cleaning. If the commutator had black burned spots or pitting, I would have sanded it with garnet sandpaper--the particles are non-conductive. Do not use emery cloth or aluminum oxide abrasive cloth due to the conductive particles. The mica between the copper segments needs to be slightly below the surface of the copper, and can be scraped down if needed.