Yamaha Rd250/350 Powerband "Fix"
YAMAHA RD250/350 POWERBAND "FIX"
PRODUCT EVALUATIONS
DH Enterprises manufactures an unusual “performance” accessory for Yamaha RD250s and 350s. The company’s reed spacer kit is not designed to pump more power into the already potent Twins, but rather to make them easier to ride on the street. For, along with all the horsepower the Yamahas deliver, an owner has to put up with lots of clutch-slipping and high revs to get going from point A to point B, with a few hair-raising wheelies in between.
A powerband that starts 1000 rpm lower than standard is what bolting on DH 10mm spacers between each reed cage assembly and cylinder delivers. Removing the carbs and reed cages, and cleaning the gasket surfaces, makes the initial installation at least an hour-long job for an average worker. Four reed cage gaskets not supplied with the kit must be purchased from your local Yamaha dealer. Four extra-long bolts are also required. The gasket part number is 314-1 3621-01, bolts are 91104-06035.
Smoother, less nerve-wracking starts are possible with the spacers in place. It was no longer necessary to rev our stock RD350 as high when riding away from a stop. And chances of unexpected wheelies were reduced. At the same time, intentional wheelies were not impaired.
The spacers do not increase top-end performance. In fact, we could not tell any difference in top end by riding the stock test bike with the spacers.
Just to see what would happen if the spacers were installed on a highly-modified 350 motor, we then put them on Scott Clough’s Production class road racer. According to Ron Black’s Stuska pump dyno, the spacers increased maximum torque 2.5 percent, while raising the torque peak 200 rpm. They also knocked off 1.5 hp at the 7000 rpm horsepower peak. Throughout the racer’s powerband, the spacers caused as much as a 4-hp loss. With the spacers, Scott’s trick 350 pulled down to 6800 rpm; without, it would pull all the way from 6200 rpm.
What does it all mean? If you’re into racing, and don’t mind having to rev and slip a lot to get rolling, preferring instead sky shots and startled pedestrians, don’t buy DH spacers. On the other hand, if you want your RD to be a little more tractable, especially in traffic, and if you don’t play G.P. on or off the track, the DH spacers might be just what you need.
The spacers cost $5 each from your local Yamaha dealer or DH Enterprises, 4909 Compton Blvd., Lawndale, CA 90260.
