Length of track is not an issue.
Use power taps to improve conductivity plus clean all connections with a lubricant like INOX. Make sure each connection flows current.
A good trick is do not complete the circuit leaving the last track back to the Power Base unhooked, drive your car slowly around the track, if it slows dramatically or stops inspect the last connection and fix the conductivity before going on. Once the car will drive slowly all the way around your circuit back to the gap before the power base hook that piece up and you should have a good running track.
Make sure rails are tight in the road bed, especially with magnets as they will lift loose rails causing poor running of cars, as the track disconnects.
Hope this helps some.