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Old 04-30-2013, 01:54 PM   #6
Beastly Adventurer
Joined: Mar 2013
Location: Imperial Valley, California
Oddometer: 3,081
Here is my favorite way to jet Carburetors, firsts off you need to have the bike properly timed and good sparkplugs.

either go to a drag strip that has bracket racing or get a friend or two and a stop watch.

Find out your 1/4 mile time with existing main jets and with jets that are richer and leaner, (be certain to always shift at the exact same RPM). This actually works best if there is a mild uphill slope. If leaner jets make you faster then ge even leaner until you start to go slower, same deal if richer, richen it up until it slows down, then go back to where it was fastest.

next to set your needle, put some masking tape on your throttle grip and another on the switch housing by your throttle grip, draw a line which matches up when you are close to 1/2 throttle, time yourself but only use 1/2 throttle as indicated by your marks on the throttle, raise the needle and check your time again, try the different needle positions and use the one that gives you the best time.

If you can't get to a dragstrip and all your friends are busy you can test your accelleration between two points, ie:find two signs or other obvious objects about 1/8th of a mile or less apart, approach at 40 mph in 4th or 5th gear then open it up all the way as you pass the first mark point then observe your speed as you pass the second point, to set your needle position use 1/2 throttle, make sure you are using the same ammount of throttle for each test run.

again if you can, going uphill will be a good idea as it will reduce your top speed.

After you get your mains and needle position sorted out, pick a low speed jet that allows you bike to idle best with the idle mixture screw set between 3/4 to 2 turns out.

carry paper and write down your results, including date, temperature, weather and time of day. The jets effect each other so expect that the best idle jet may change as you use different mains and move the needle,
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