Quote:
Originally Posted by Megadan
The number one reason people brought their bikes in to the shop feeling frustrated because they couldn't get it to run right summed up in one sentence. Nobody takes the time to understand that there is more than 1 jet, and more than one circuit per jet.
The other big mistake is people will use the needle as a bandaid to other jetting issues.
Things the uninitiated should understand:
Pilot jet affects idle mixture AND low throttle. You might be able to get a good idle mixture setting, but the engine may still be too lean/rich under light throttle causing running issues. Just because the idle mixture works, doesn't mean
The main jet affects the needle jet and needle fueling just as much as it does the 3/4 to wide open range. Example: My PZ30b required the needle to be dropped down a notch when I went to the 125 main jet from the 120 because it was letting enough fuel through to become too rich.
It is important to find the main jet that works best and then tune the needle last. Not just in height, but diameter and taper as well. While this may be a little difficult to do with the cheap clone carbs, if you get something like my Nibbi that comes with a size stamp on the needle, this can be used to tune the mid range. Length of the straight section, diameter of the needle body, and taper can be used to tune the lower and upper halves of the fueling curve the needle provides. A larger diameter will lean out the bottom half in relation to the top half, where a more aggressive taper will richen the top half vs. the bottom half. A longer or straight section before the taper will alter how soon the needle starts to contribute fuel, which is great for dialing in jet transitions.
Getting jetting dialed in as precisely as most OEMs have to do is a very tedious process, because one change in one area may require changing another.
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Yes, I agree completely. Especially about jacking the needle up and down, looking for Nirvana. I thought what I wrote was too long already or I would have recommended setting the needle in the middle slot (or removing the washers) either before or after the pilot jet is set to your satisfaction. Then do the main jet. You should use the needle slots to fine tune the mid-range only....ARH
