Posted by keith on November 21, 1999 at 21:57:32:
In Reply to: Voodoo Mechanics posted by keith on November 21, 1999 at 10:26:55:
Witch Doctor is right about non-restrictive exhaust systems decreasing power, but I believe this is a phenomenon particular to multiple cylinder engines. The multiple cylinder engine with a header, for example, actually creates a vacuum, or more specifically, a purging action in the combustion chamber during the exhaust stroke.
The escaping gases of the cylinder leave the exhaust system at high velocity creating a partial vacuum in the exhaust system. When the next cylinder begines it's exhaust stroke, this vacuum purges the cylinder as the exhaust valve opens. Apparently, the effect is very pronounced at high rpm's, leading naturally to significant imbalances in the un-tuned engine. About fuel injection. Carburators and fuel injection both supply fuel to the engine and thats where the similarity ends. True, carburators can be adjusted to varying extents, and this can have serious effects on engine performance. On the other hand, computor controlled injection provides a precise charge to the airstream at precisely the right instant. Consider the staggering horsepower delivered by today's emissions legal sports cars. In relation to adusting the mikuni carb, I am simple not knowledgeable. As Ken points out, tuning is an art, and it does vary with atmosphereic conditions, altitude and other factors(fuel injection does this several times per second), but based on my limited experience, I doubt that much valuble adjustment is available on the stock Mikuni. Really, we ought to ask a Suzuki engineer in Japan. P.S. to Ken, in some carbs the order of circuits is as follows; idle, off idle, transition, intermediate, cruise, power enrichment, and of course the accelerator pump operating every time the accelerator is depressed. The cruise is adjusted by changing jets and neddles(a matched set). I do not believe that many of the adjustments made on auto carbs are available to motorcycle carbs, hence necessitating replacement.