I am wanting to tweak my fuel screw and from what I have read, you put the bike at a high idle and adjust the fuel screw in until the RPM's drop way down. Then you turn it back out and stop as soon as the RPM's stop going up. Does everyone do this by Ear? I would like to use a tach for possibly better accuracy. Is there a good, reasonably priced, and easy to use tach out there that anyone would reccomend?
Tach for Tuning?
Started by Dude13, Feb 25 2003 06:14 PM
5 replies to this topic
Posted 25 February 2003 - 06:14 PM
I am wanting to tweak my fuel screw and from what I have read, you put the bike at a high idle and adjust the fuel screw in until the RPM's drop way down. Then you turn it back out and stop as soon as the RPM's stop going up. Does everyone do this by Ear? I would like to use a tach for possibly better accuracy. Is there a good, reasonably priced, and easy to use tach out there that anyone would reccomend?
Posted 26 February 2003 - 04:50 AM
I picked up a neat little digital tachometer at my local small engine repair shop. All you do is wrap the sensing wire aroung the spark plug wire a few times and you are ready to go! It cost about $30.00 but I feel it was worth it because I use it for sound testing and I need to know exactly what the RPM's are. There are also little vibrating tachometers that you simply select what RPM you want, this extends a little wire out of the unit, when the wire starts vibrating, you have reached that RPM. This vibrating wire tach should be available through a small engine repair shop also.
Posted 26 February 2003 - 05:11 AM
Dude,
I'm not sure what you consider reasonably priced, but this high rpm tach could work full time for ya. SenDEC has several others which may fit your budget/purpose, check them out.
I'm not sure what you consider reasonably priced, but this high rpm tach could work full time for ya. SenDEC has several others which may fit your budget/purpose, check them out.
Posted 26 February 2003 - 06:21 AM
Most do it by ear, especially at the track. But there is a procedure to do it with a tach and this also helps to better select what size pilot jet you need. Here is the procedure I use:
1. Record the Alt and Temp for future reference (I don't bother with RH, its always dry here but if I lived elsewhere I might). Write everything down.
2. Warm the bike up by riding about 10 minutes. Place it on a stand, have it idling. If you have a fan, direct it into the Rads. (A YZ will start to boil out if you take too long to do this, WRs have a nice catch tank). My guess is its better to do this with adequate cooling.
3. Turn the fuel screw 1 1/2 turns out. Attach the Tach to the plug lead and turn on the display. Read the RPM for about 10 seconds (on my tach, cause it bounces around). If the avg RPM is not between 1700 and 1900, adjust to about 1800 with idle screw knob on carb. Write down avg RPM.
4. Turn the fuel screw 1/2 turn out. Write down the average RPM.
5. Turn the screw 3 turns out. Write down the average RPM.
6. If #3 is greater than #4 or #5, you have the right pilot jet. Usually the difference will only be 50 to 100 RPM. Go on to step #7.
If #4 is greatest, you need less fuel. Install the next smallest number pilot jet. Go to step #3 and repeat.
If #5 is greatest, you need more fuel. Install the next largest number pilot jet. Go to step #3 and repeat.
7. Adjust the fuel screw in 1/4 turn increments around 1 1/2 turns out and find the maximum RPM fuel screw position. If the idle is now above 1900 RPM, turn it down to be in spec. I like mine closer to 1900 than 1700.
8. If you get a little decell backfiring on closed throttle, try adding another 1/4 turn out. Rememeber you will need to redo this if you change temps and alts, but at least you will have a starting point.
You don't need a high rpm tachometer. Sendec also makes several tachs with rpm ranges suitable for tuning (~7000). Here is a link to Sendec Tachs
1. Record the Alt and Temp for future reference (I don't bother with RH, its always dry here but if I lived elsewhere I might). Write everything down.
2. Warm the bike up by riding about 10 minutes. Place it on a stand, have it idling. If you have a fan, direct it into the Rads. (A YZ will start to boil out if you take too long to do this, WRs have a nice catch tank). My guess is its better to do this with adequate cooling.
3. Turn the fuel screw 1 1/2 turns out. Attach the Tach to the plug lead and turn on the display. Read the RPM for about 10 seconds (on my tach, cause it bounces around). If the avg RPM is not between 1700 and 1900, adjust to about 1800 with idle screw knob on carb. Write down avg RPM.
4. Turn the fuel screw 1/2 turn out. Write down the average RPM.
5. Turn the screw 3 turns out. Write down the average RPM.
6. If #3 is greater than #4 or #5, you have the right pilot jet. Usually the difference will only be 50 to 100 RPM. Go on to step #7.
If #4 is greatest, you need less fuel. Install the next smallest number pilot jet. Go to step #3 and repeat.
If #5 is greatest, you need more fuel. Install the next largest number pilot jet. Go to step #3 and repeat.
7. Adjust the fuel screw in 1/4 turn increments around 1 1/2 turns out and find the maximum RPM fuel screw position. If the idle is now above 1900 RPM, turn it down to be in spec. I like mine closer to 1900 than 1700.
8. If you get a little decell backfiring on closed throttle, try adding another 1/4 turn out. Rememeber you will need to redo this if you change temps and alts, but at least you will have a starting point.
You don't need a high rpm tachometer. Sendec also makes several tachs with rpm ranges suitable for tuning (~7000). Here is a link to Sendec Tachs
Posted 26 February 2003 - 05:45 PM
WOW Rick!! You spent some time on that for me. This will really help out. One more question though. On my 03, there is no spark plug wire. The coil sits right on top of the plug. I dont know if the other years are like this. The tach that You and Dirt Surfer refrenced hooks around the plug wire. How would you hook it up then?
