lelocp wrote:i took the bike and did a main jet test and i have to say everything seems spot on but there's one thing i noticed about these carbs, that is that there is no spring at the diaphragm. It's really hard to get any information on these set of carbs. Do you think there should be a spring? Any way to tell by just running the motor and what effect does the spring have?
The springs slow the rise of the pistons when accelerating which causes a rise in air velocity through the venturi which in turn results in a temporary rich condition. You can think of it as an accelerator pump affect. They were used to allow leaner mid-range settings without losing acceleration performance. In other words without springs the mixture would have to be richer to avoid an acceleration flat spot. In the mid 80's the springs where stiffened presumably to allow even leaner settings for emission testing reasons.