Carb Technical ? Jet Sizes

[CJ428CJ]

With a Demon carb, I always thought the term "as close to square as possible" refered to the transfer slot opening rather than the size of the jets. If you take the carb off and turn it upside down, there's a transfer slot running vertically down the venturi. The butterflies are supposed to be adjusted so the visible part of that transfer slot is square rather than rectangular. If you have low vacuum, the power valve will stay open at idle causing a very rich condition. The natural tendency of someone incorrectly tuning the carb is to turn the idle butterfly screws in causing the butterflies to open. This will help the engine idle but it causes the transfer slots to be very rectangular rather than square and the engine will continue to run very rich. Instead of opening the butterfly idle screws, a correctly sized power valve should be installed (1-2 inches lower than idle vacuum). The transfer slots should then be squared up and the idle mixture screws should be adjusted to get the idle as close to perfect (fast) as possible. Only then should the butterfly idle screws be adjusted a very small amount to fine tune the idle.