To understand how the jets interact (how the carb basically works)...
The upper portion of the carb consists of cylindrical slide with a spring-loaded needle at the bottom which is controlled by a vacuum-actuated diaphragm. I am a little fuzzy right now as to how it exactly works, but, basically, the cylinder blocks the carb body and acts as a second throttle plate (or perhaps even a venturi
).
Anyway, when the throttle is opened, the slide lifts with its needle, the slide allowing in more air, and the needle allowing in more gas.Remember I said that the main jet is threaded up into the needle jet? The fuel comes up through the main jet, then has to deal with the needle jet, The needle rests down into the needle jet. The needle acts as a fuel restrictor. When the needle is lifted to its maximum, the main jet is the main fuel bottleneck.
The main is supposed to make the most difference at full throttle.
The needle jet (needle position is what we're concerned about here) makes difference off idle and part throttle. Richening that up a bit (compared to stock) will help response.
The idle jet (the only quickly adjustable one) makes the most difference-- DUH!-- at idle.
Adjust this one as follows: With idle speed reasonable, turn counterclockwise to richen, clockwise to lean, if I am not mistaken. Aim for the midpoint position where the idle speed is the greatest for the same idle speed (throttle plate position). Very easily understood hands on. Set the idle speed adjustment (you know, that little spring-loaded fingerscrew on the throttle cable cam thingy.
) Then, turn the idle screw one way till it speeds up and runs best, but keep going until you've gone a little too far. Go until it slows down
slightly. Stop, then go the other way until it reaches its sweet spot, then passes it and slows down
slightly Then go back halfway. This should be the sweet spot for those conditions.
Remember that this should be done after driving the bike and getting it nice and warm. In summary, the idle mixture should give the highest idle speed for the least amount of throttle (or the highest vacuum, as some would say).
Now, you're brain is fried, and you're still wondering about the spacer mod? It works like this. There is a white plastic spacer on that spring-loaded slide needle which pushes it down into the needle jet. Shaving down this spacer (plastic washer) or replacing it with a thinner equivalent of #4 washers will allow the needle to lift up a bit and allow more fuel in at part throttle. This is accessible from the top of the carb. Lift the diaphragm slide out. Note that the screws on the cover could be difficult to remove.
Do not strip them! Way down there in the slide are two little screws which hold a plate. Remove these, and you'll find the spring and needle with it's white spacer. Here's where you can replace the white spacer with washers or grind down the spacer. A magnetic screwdriver will be helpful here to get the screws back into place. The plate, spring, spacer and everything goes on a certain way. I think there's a little metal washer in there as well below the stationary e-clip that the spacer rests on or something like that. You'll know what I'm talking about when you get it apart.
Got it?
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