For the last few trips, I figured my lower top speed was due to a damaged battery in my pack. However, I noticed even if I totally opened up the throttle, the batteries would dip a little but still stay in the upper green. So I figured something else must be wrong. On the last few trips, I would think I would smell something that seemed electrical or possibly a dragging brake but I could never pinpoint it. Then, today, when in a 40mph zone, I noticed I could not get above 30 on flat roadway with the throttle wide open and still in the green!
When I got home, I Immediately inspected the BugE to see if I could pinpoint the problem. The rear parking brake was cool. The front brakes were warm as expected but not excessively hot. The splash plate had come undone and was rubbing against the tire but that would not possibly be enough to slow the BugE down that much. The motor controller was cool too.
Finally, I inspected the motor. Very hot! At first, I thought the chain may have been miss-aligned. It had a little slack in it but it looked OK and had plenty of grease on it. The sprocket teeth also looked OK too. So, I re-aligned the rear tire, tensioned the chain and took it for another test drive around the block. Same thing - poor top speed and the motor heated up again. Normally, the motor runs cool so this was very unusual. The last symptom was that that the motor now makes a sound similar to what I thought was a miss-aligned chain drive. However, when I took off the drive chain, I noticed the sound was still present! It was quite a bit different from the "Boba-Fett" whine it normally makes when underway.
I then decided to take the end motor cover off to check the brushes. No signs of rust and it was not terribly dirty. What I did find was a very uneven commutator pickup with lots of carbon on it and an end bearing that did not turn very well. When operating, the brushes were bouncing up and down quite a bit! That apparently was where the "chain sound" was coming from.
So, I contacted the Advanced DC motor people. They recommended a motor shop relatively near where I live. Since the motor is more than two years old, this problem isn't covered by the manufacturer. However, the repair place I took it to replaced the whole "core" and gave me a new 6 month warranty. Although it was no fun paying for that, there was one bright spot. Unlike a car or even a street motorcycle, it was easy for me to extract my motor and bring it to the repair shop myself.