How to fine-tune your jetting: Difference between revisions
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[[Category:Intake]] | [[Category:Intake]] | ||
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'''Note:''' For the same general information presented a different way, [[Rejetting after installing pod filters|clicky]]. | |||
==Before you start== | ==Before you start== | ||
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The best solution is taking the bike to a professional with a Dyno and an EGA (electronic gas analyzer, sometimes called a "Sniffer" or "4 gas analyzer") to see what kind of exhaust the bike is putting out at the different RPMs while under appropriate load. The next best solution is to dive head and heels into the massive amount of jetting information that's been published. There are dozens of different books dedicated to the subject. You'll have to read, then apply the information learned so you can feel what lean and rich are like. There's absolutely no way to impart that knowledge in the space of the FAQ. | The best solution is taking the bike to a professional with a Dyno and an EGA (electronic gas analyzer, sometimes called a "Sniffer" or "4 gas analyzer") to see what kind of exhaust the bike is putting out at the different RPMs while under appropriate load. The next best solution is to dive head and heels into the massive amount of jetting information that's been published. There are dozens of different books dedicated to the subject. You'll have to read, then apply the information learned so you can feel what lean and rich are like. There's absolutely no way to impart that knowledge in the space of the FAQ. | ||
You may want to [[Battery box mod for easier carb removal|modify the battery box]] if you are going to put an aftermarket exhaust on your bike or otherwise plan on rejetting. Why? Because the physical carb adjustment is simple. It's the fine tuning process that can be time consuming and tedious. It will require you to pull the carbs AT LEAST TWICE (if you are extremely lucky), but probably more like three or four times to get everything right. | |||
==Carb adjustment== | ==Carb adjustment== | ||
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Remove the black covers on the top of the carbs. The screws have different lengths, so keep track of which one goes where. The plastic vacuum pistons are held under pressure by a spring, so be careful when removing the top. | Remove the black covers on the top of the carbs. The screws have different lengths, so keep track of which one goes where. The plastic vacuum pistons are held under pressure by a spring, so be careful when removing the top. | ||
Carefully pull the vacuum diaphragm/piston unit out. The rubber diaphragm is the most delicate part of the carb | Carefully pull the vacuum diaphragm/piston unit out. The rubber diaphragm is the most delicate part of the carb and is easily damaged. | ||
Shake the needle out, raise it with (however many) 2.5 or 3 mm washers. | Shake the needle out, raise it with (however many) [[Washers for carb needles|2.5 or 3 mm washers]]. | ||
*If you're using aftermarket needles, start with the clip in the 3rd position (middle). This is usually for a stock or mildly modified setup, such as a slip-on exhaust. You can use washers to make "half" steps, too, for super-fine tuning. | |||
Reassemble. | Reassemble. | ||
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Raising the needles can actually be done without removing the carbs from the bike. Pull the tank, without pulling the upper fairing. You'll need a good-condition #2 phillips screwdriver with a shaft about 10" long. A multi-bit screwdriver won't work because the shaft is too thick. Just slide the screwdriver through the brackets to pull the screws out, pop the cover off, pull the springs, and fish out the vacuum pistons. Make your adjustments and reassemble. Make sure to drop the needle straight down, so that it goes into the collar above the emulsion tube; you can easily see if it doesn't. Put the screws and brackets back on, and you're good to go. | Raising the needles can actually be done without removing the carbs from the bike. Pull the tank, without pulling the upper fairing. You'll need a good-condition #2 phillips screwdriver with a shaft about 10" long. A multi-bit screwdriver won't work because the shaft is too thick. Just slide the screwdriver through the brackets to pull the screws out, pop the cover off, pull the springs, and fish out the vacuum pistons. Make your adjustments and reassemble. Make sure to drop the needle straight down, so that it goes into the collar above the emulsion tube; you can easily see if it doesn't. Put the screws and brackets back on, and you're good to go. | ||
The big key to this is to not have sticky bolts... If they are stuck, you'll need to pull the carbs so you can put them in a bench vise and hit them with an impact driver. | The big key to this is to not have sticky bolts... If they are stuck, you'll need to pull the carbs so you can put them in a bench vise and hit them with an impact driver. | ||
====Step 4: [[Removing idle mixture screw plugs|Adjust mixture screws]]==== | ====Step 4: [[Removing idle mixture screw plugs|Adjust mixture screws]]==== | ||
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====Step 5: [[How do I remove the carbs to work on them?|Attach carbs to bike]]==== | ====Step 5: [[How do I remove the carbs to work on them?|Attach carbs to bike]]==== | ||
==Carb Tuning== | ==Carb Tuning== | ||
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====Step 1: Find the proper main jet.==== | ====Step 1: Find the proper main jet.==== | ||
Start from the stock jet and needle height, and increase the main jet size by ONE SIZE at a time, until you feel the upper too rich. Then back up to the previous size. Please note that the amount of gas passed by the main jet increases exponentially with main jet size, as the circumference of a circle increases exponentially with diameter! What that means is that the difference between jet sizes is not equal. | Note that you will have to buy 2 jets of each size, one per carburetor. Start from the stock jet and needle height, and increase the main jet size by ONE SIZE at a time, until you feel the upper too rich. Then back up to the previous size. Please note that the amount of gas passed by the main jet increases exponentially with main jet size, as the circumference of a circle increases exponentially with diameter! What that means is that the difference between jet sizes is not equal. | ||
'''Example:''' | '''Example:''' | ||
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====Step 2: Find the proper needle height.==== | ====Step 2: Find the proper needle height.==== | ||
Start from tuned jet | Start from the tuned jet that you decided on in step 1. Use the stock needle height, and keep raising the needles by adding washers. If it runs better with more washers, then, when you get to about 4, go up a size on the main jets and start with the stock needle height again. | ||
Even after you get the main jet correct, you will often end up with a midrange stumble at 5k-6k rpm. This has little to do with main jet size. You can take care of it by adjusting the needle height. Lower the needle until you get a mid-range stumble, then raise it by 1 washer at a time until you get rid of the stumble. | |||
Symptoms: | Symptoms: | ||
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LEAN = Stuttering. Runs better when bike is hot. White plugs. | LEAN = Stuttering. Runs better when bike is hot. White plugs. | ||
RICH = Bogging. Runs better when bike is cold. Black plugs. | RICH = Bogging. Runs better when bike is cold. Black plugs. | ||
====Step 3: Find the proper idle mixture.==== | ====Step 3: Find the proper idle mixture.==== | ||
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Symptoms: | Symptoms: | ||
LEAN = Blipping throttle causes the | LEAN = Blipping throttle causes the rpm to rise, hang for a moment, then drop back down. | ||
RICH = Blipping throttle causes the | RICH = Blipping throttle causes the rpm to rise, drop down below the idle speed setting, and the rise back up. | ||
==Conclusions== | ==Conclusions== | ||