Are they really needed for the overall average mx rider !! ?
cheers A
Al,
On a late model water-cooled 125/250 the difference between them working and not is substantial. In fact that reason that current 2 strokes, particular the larger capacity engines, are so rideable is due in part to the fitment and correct tuning of the power valves. Obviously head design, carburetion, exhaust etc plays a big part but the power valve is key to all this working. For the KTM range, the adjustable power valve on the 300EXC is a perfect example. The bike can be a arm tearing motocross monster or a sedate trail bike, all by the adjustment of the power valves and associated jetting.
Mark,
Know too well the 250F / 450F saga. I see it day in, day out with kids buying their first 2nd hand motocrosser only to learn a few weeks later that they need greater than the purchase price, just to fix the engine. The other issue with these titanium valved bikes is that there are very few engineers around that can “CORRECTLY” set up the cylinders heads to get the maximum life out of a new set of valves.
It was once described to me that Black Magic is the main ingredient in getting the valve seat angles, valve spring rates and installed tensions etc correct.
