wire connection? maybe there is an inconsistent short somewhere in the harness?
my former 94 EX Coupe had this problem. Replaced the motor and it was still kind of slow and I started thinking it may have been a wiring issue. Never got to hunt it down because I sold it.
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if you can only race me in a straight line then whats the point 
...91 SMF SCCA
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by http://www.flickr.com/people/8341770@N07/, on Flickr
I see people out there spending money on the car to improve it … If you spend half that effort just working on your driving skills, making you and the car work together as a team, then you’ll go faster – period. To make the car go a second faster on the track takes a lot more energy and money than making yourself drive it one second faster.
– the late Tom Thrash SCCA Solo E Production