I have just carried out a mod. to the starter motor of the Honda GL motor that's going into my 3 Wheeler,and which I have just finished preparing, and seems to work. The negative earthed return circuit in the Honda starter motor is via a "wiping" ,or clamped contact on the brush holders of the motor. This is only kept in contact with the motor body by the pressure of the endcap,( check for burning between the top brush holder metal tangs and the body of the motor), and its long fixing screws, and can lead to arcing and hence a "slow" motor turnover. What you do is drill and tap the alloy end cover 3mm, then fit a 50mm long flexible lead to connect the Brush holder ring to to the end cap, making a firm, sound, and permanent, return connection. It definitely increased the speed and reliability of my starter motor, and would probably apply to other manufacturers engines, so if you have a problem, or are just o/h your starter, its worth considering, and simple to do. I picked the idea up from another Forum, so its no revelation on my part!!
Morrag
