Info:Adjustment

The engine is carbureted in the factory before delivering, do not not try to modify the carburetion if you do not know how.

With a "lean mixture" the engine is more even but it gets overheated (usually there are "blanks" in the carburetion)

After 10 minutes of working, the spark plug will start to get dirty with fuel waste.

spark plug dyeing	yellow/gray	hazel brown/light brown	brown/black
carburetion	lean	right	rich

How do I adjust my Carburetor?

First of all, locate the "L" and "H" markings on the carb case. These markings are located next their corresponding "Low" and "High" speed needle valves. The "Low" speed screw is the short flathead screw valve for screwdriver adjustment. The "High" speed valve is taller and has a "T" handle for finger adjustment.

Step 4: Start the engine (you may need to adjust the low-speed screw slightly in one direction or the other to get the motor started).

Step 5: Once the engine starts and warms up for a minute, adjust the low-speed screw until the idle is as slow as possible without stopping the motor. This will give the maximum rich setting at low RPM.

Step 6: Hold the throttle wide open (with the rear tire off the ground of course) and adjust the high-speed screw to achieve maximum RPM.

Step 7: Important! Once maximum RPM is achieved, open (unscrew) the high-speed needle 1/16 of a turn. This will ensure that the engine has sufficient lubrication when running at high speed and adjusts for the load of your weight upon take-off.

Repeat steps 5 through 7 until you get a steady idle, smooth throttle transition, and maximum RPM.

Carburetion for an engine mixes gasoline with air forming a highly combustible vapor that is injected into the cylinder. As you know, the air density and level of humidity, makes a big difference in this mix process. You will find that if you live in pretty much constant air density - no large fluctuations in humidity - you will not have to adjust your carburetor nearly as much as you do if you live in Florida. There the humidity can go from 50% to 100% in the span of a couple hours.

Setting up your 2-cycle Tillotson Carburetor.
With today's state of the art motors and stinger type exhaust systems, the following information will help you achieve the desired results that you need from these motors. Before mounting your Tillotson carburetor check the pulse track from the carb mounting surface and make sure that this track through the carb adapter , gaskets and etc is clear and in line with each other.
Set the low speed needle at 1+1/2 turns out and the high speed needle at 1+1/8 turns out. Adjust the throttle stop screw on the carburetor so that it just cushions the butterfly when the throttle valve goes closed. Do not set the carburetor so that the engine will idle as this will cause the engine to lean out in the corners and anytime you are off the throttle.

Track tuning your Tillotson Carburetor.
If the carburetor settings are too rich ( too much fuel ) the engine will falter at that section of the track corresponding to that particular range of the carburetor settings. A spluttering or irregular firing sound will be heard. This sound is also called 4 stroking. If this sound occurs at low speed while at full throttle, such as coming out of a tight turn, it is usually due to the Low Speed adjusting needle being turned out too far. If the sound occurs at high speed while at full throttle, such as on a straightaway section of the track, it is due to the High Speed adjusting needle being out too far. In either case, needle adjustments must be made inwards gradually, in approximately 1/8 turn increments. It is best to adjust the Low Speed needle first for best overall low speed performance and then follow with the final high speed adjustment.

If the engine does not 4 stroke or give the too rich firing sound, any place on the track, it could be because the engine is running too lean ( not enough fuel ). This is easily checked by opening the needles out in 1/8 turn increments until the engine 4 strokes. In general, the optimum performance and engine reliability will occur at carburetor settings just slightly leaner than the point where the engine will begin to 4 stroke.

If you find that the engine will not chop off clean or is slow to come back from high rpm's when you lift the throttle, this is a sign that the pop-off pressure in the carb is too high. The cure for this is to lower the pop-off pressure. If you experience loading-up problems, this is a sign that the pop-off pressure may be too low. The cure for this is to raise the pop-off pressure. As a general rule of thumb, the pop-off pressure will be from 8 to 12 lbs, and is a tuning factor that you can adjust for the altitude of your racetrack and the type of racing that you do.