SETTING UP YOUR 4 CYCLE TILLOTSON CARBURETOR

Due to the way your Tillotson Carburetor has been blueprinted and the pop-off pressure set, the needle adjustment and the track performance will vary. The following is only a starting position for the needles. From this point on track tuning will be necessary to dial in the Tillotson that you have. Limited Modified, and Opens: Low Side Needle out 1 ¼ to 2 ½ turns. High Side Needle ½ to 1 ½ turns out. If your carburetor won’t dial in somewhere in this range then you will have to change the fuel discharge posts or pop-off pressure.


TRACK TUNING YOUR TILLOTSON:

Set the needles one (1) turn out on High Side and 1 ¼ out on Low Side for starting position be sure that the carburetor idle screw is set where it just cushions the throttle plate when it closes but not open enough so that the motor can idle. Start the engine and move out onto the track. Give the motor a couple of easy laps to warm up. Be sure in these warm up laps that you are running the motor in a spot where it is running clean. Now bring your motor down to parade lap speed. Accelerate hard as you would for the start line break. If you have a flat spot or a bog problem, this could be due to a lean condition on the Low Side Needle till the motor pulls hard with no bog or flat spot. Now try the same test coming off the turn. Once you are satisfied with the performance off the bottom and the motor pulls clean, you are ready to turn your attention to the top end.

With the motor under full throttle it should run clean all the way to the end of the longest straightaway. If the motor shuts off then comes back on by itself before you get to the end of the longest straightaway this is more than likely do to the fact that the carburetor is set too rich on the High Side Needle. The cure here is to take the High Side Needle in (lean out) 1/8 turn increments till the motor pulls clean the full length of the straightaway.

As you lean in the High Side Needle for the best top end power you are also leaning out the bottom a touch. So, to assure yourself of good corner speed and no flat spot off the bottom you need to go back now and check for this one more time. As you can see, the tuning of a Tillotson on a 4 cycle is a fine balance line between the High Side and Low Side Needle adjustments plus the pop-off pressure in the carburetor.

NOTE: Methanol fuel is a very high corrosive type of fuel and should never be left in the carburetor when the day or night of racing is over. Be sure and flush the fuel pump and carburetor out with gas. If your Kart has an alloy tank on it be sure and flush it out also. As far as fuel tanks go, a plastic fuel tank is the best choice for methanol fuel.