If you've thought about any kind of competitive racing you should consider lapping the gears. Its not difficult and you just might like the results. Your can achieve anywhere from 10 to 15 percent increase in speed just by lapping the gears on the gear plate.
First of all I have a gear lapping contraption I use to keep the mess to a minimum, my lapping tub, my power source, which consists of a 9 volt battery and a 9 volt battery pig tail with some alligator clips. If you would like more information about how to build the tub check here.
Second I have my gear lapping material Simichrome which you can find on Ebay.
I mount the chassis in the tub.
I then apply the Simichrome to the top gears using a toothpick. I apply around the edges of all three gears. I then connect the the alligator clips to the top of the pick-up shoes and connect the battery. The motor will start turning. as it turns the pinkish Simichrome will start turning grey in color.
Whie the motor is running, the Simichrome will start to turn grey in color, take your toothpick and start removing the grey Simichrome. Once it's removed replace what you have removed with new Simichrome using your toothpick. Get a little dab of Simichrome on the toothpick and lightly touch the edge of each gear. You will see the new Simichrome spread on the gears. Continue this process for about 15 minutes. About half way through reverse the alligator clips and run the chassis backwards so you lap both sides of the gears.When finished you should have a chassis that looks like the picture below.
Remove the chassis from the tub and take it apart. Then clean it with a toothbrush and warm water. After that you will still have some Simichrome residue left.
The best way to remove this residue is to use an ultrasonic cleaner along with a liquid cleaner. With respect to the liquid cleaner I use half water and half 409 cleaner degreaser. I put the parts in the ultrasonic cleaner for a minimum of 20 minutes but no more than 30. You can get a cleaner on Ebay relatively cheap.
When I take the parts out of the cleaner, I rinse them off with warm water and then pat them dry with a paper towel. I then follow this up with drying the parts thoroughly with a blow dryer. When you are sure everything is dry then put the chassis together, oil the chassis well, and then let it run. It will be quieter, smoother and faster!!!