Model years 1985-1989
86 TRX250R
The Honda motor that helped put ATV racing on the map was the first water cooled design that first made its way into one of the ATV's. It first appeared in the 1985 ATC250R. After heavy pressure from multiple lawsuits and the U.S. government agency CPSC lead Honda to basically transplant the motor into a 4wheeled version named the TRX250R. It is presumed that continuing legal pressure prompted Honda to pull the high performance ATV "R" line up. Though the motor was designed to be tame in comparison to the same years CR250R 2-stroke motors, the momentum from the mounted pressure of the huge bad press the ATC originally got, meant among other things that the R would never really pickup the type of stock power Honda's motocross customers were seeing. As a side note, it is interesting possibly that falling off a motorcycle is much easier than falling off an ATV, but the ATV's received the most bad press and the least powerful engines.
Fortunetely, the stock motor is easy to modify so that it puts out hp numbers closer in line with racing motorcycle engines. A well running, modified TRX250R motor in a chassis with some upgraded suspension is a white knuckle, riding on rails experience. For a thrilling ride experience it's a hard design to beat.
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Easy to fix weak areas
There aren't many structural weaknesses to the stock motor in stock form. Compared for example to a Suzuki Quadzilla LT500, there are no head stud issues, main bearing support problems, vibration related failures, etc. There are however some simple performance issues that once cleaned up, significantly wake the stock motor up without losing reliability:
Intake
coming soon:
head
pipe
coming soon:
Ah, a structural problem in the clutch! No major issue... it's easy to fix. See here:
Stock porting and port timing observations and specifications: