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Difference between revisions of "Jetting"
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Reverted edits by 69.158.150.65 (Talk); changed back to last version by Kevef
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==Fuel Screw== | |||
The Fuel Screw is mis-labeled in the Yamaha manual. It is labeled as an "Air Screw". This is 100% backwards. Air screws are on two stroke carbs. The last I checked, this carb has been on this 4 stroke engine. | |||
The fuel screw allows more fuel through the pilot circuit. This very definitely affects low speed operation. To allow more fuel flow or richen up the bottom end, the fuel screw is turned counter-clockwise (or turned OUT). This IS richening up the bottom end. | |||
To lean it out, the fuel screw must be turned clockwise (or turned in). The problem with this low speed/idle jetting is it is too lean. The only time I think you would turn it in is if you decide to ride your TTR into the Rockie Mountains, where bikes are starving for air, which ain't there! | |||
==Pilot Jet== | ==Pilot Jet== | ||
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There is a clip on the needle that allows you to raise or lower the needle, effectively changing the amount of fuel flowing in this 1/4 > 3/4 throttle position. So, if you move the clip down, this effectively raises the needle. Since the needle is now higher in the carb, and we know the needle is skinnier at the bottom, MORE fuel will pass through in the midrange than before you moved the clip. | There is a clip on the needle that allows you to raise or lower the needle, effectively changing the amount of fuel flowing in this 1/4 > 3/4 throttle position. So, if you move the clip down, this effectively raises the needle. Since the needle is now higher in the carb, and we know the needle is skinnier at the bottom, MORE fuel will pass through in the midrange than before you moved the clip. | ||
As for swapping out the needle, the skinnier the needle, the more fuel allowed into your engine. | As for swapping out the needle, the skinnier the needle, the more fuel allowed into your engine. | ||
==Main Jet== | |||
At 3/4 throttle and higher, the ONLY thing metering fuel is the main jet. If your bike has problems at wide open throttle, the main jet is your culprit (unless it's your ignition...???). A larger main allows more fuel. | |||
When you modify your bike, i.e. cut your airbox lid, install a high air flow airfilter, you are changing the amount of air into the engine. | |||
When you install an aftermarket exhaust pipe, more air (exhaust) is coming out of your engine. | |||
In BOTH of these conditions, you MUST increase the fuel going to your engine to offset the air going into (or out of) your engine. | |||
Moving more air means you have to move more fuel. | |||
==Elevation & Weather Changes== | |||
When there is a change in the weather or riding elevation, the amount of Oxygen or moisture will be the culprit. At higher elevations, there is less O2 available. You will need to jet lean to decrease the amount of fuel to compensate for the lower O2. | |||
If it is humid, there is MORE water in the air, you MAY have to jet lean. | |||
In the winter, bikes run lean. Because of the lower temps and humidity, there is more O2 due to density changes. Your bike will run lean, and you will benefit w/ RICHER jetting. | |||
[[Category:Articles]] | |||