Figure 7.3-1 Adjusting the Paddle Lever Arm Height

This can be checked using the special gauge sold by TAL-KO or measured using a steel rule placed across the bottom face of the carburettor base and a small piece if 1mm diameter wire. It is important to set the Paddle Lever Arm at the correct height so that it does not load the Metering Diaphragm when it's engaged with the stud. If the Paddle Lever arm is not set to the correct height when assembled the diaphragm will be pushed up or pulled down by the Paddle Lever Arm.

Figure 7.3-2 Raising & Lowering the Paddle Lever Arm

If the Paddle Lever arm is too low (more than 1.1mm) then gently lever it up. If the Paddle Arm is too high (less than 1mm) then gently bend it down by pushing on both ends.

Adjusting the Pop-Off

If after setting the Paddle Lever Arm to the correct height the Pop-Off does not occur between 11-13psi then the force provided by the spring will need to be adjusted. There are two ways in which this can be achieved;

·         Very small changes in Pop-Off pressure can be achieved by slightly bending the Paddle Lever Arm, but the clearance must remain close to 1mm.

·         Larger changes can be achieved by altering the closing force provided by the spring. If the Pop-Off pressure is too high then compress the spring (between finger and thumb). If it is too low then extend the spring a little.

Warning! It is illegal to clip the spring!

If the the Pop-Off pressure is more than a few pounds out or when set correctly the stabilised pressure is not correct then something is wrong!

·         Ensure that the four screws holding the diaphragm cover are correctly tightened.

·         Ensure that the Diaphragm and Diaphragm Gasket are in good order and correctly assembled.

·         Ensure that the Metering Valve and its seat are clean and undamaged.

Carburettor set-up

The carburettor must be clean and the Pop-Off must be correctly set. The air filter should be clean and dry.

The author does not fully understand the science of carburettor adjustment. He has read all available publications and has listened to much advice, most of it contradictory. Set out here is a method that has evolved by trial and error.

2.1 Setting the Jets

Figure 2.1-1 Carburettor Jets

The low jet is a plain screw head and the high jet is a ?T? bar.

2.2 Initial settings

Turn both jets in until lightly seated. Turn the High jet out to ¹/₃ turn on cold days, ¹/₂ turn on hot days.

Turn the Low jet out 1¹/₄ turns on cool days and 1¹/₂ turns on hot days.

2.3 Jet Adjustment

The engine should run OK with these initial settings, but will require tuning to achieve best performance.

Note that if the mixture is too weak it can result in damage to the engine.

? If the engine smokes and four-strokes at corners then the mixture is too rich. Weaken the mixture by closing the low and high jets together in increments of ¹/₁₆ of a turn.

? If it is slower than others along the straight because it won?t rev high enough (i.e. It flattens out at below 15000 and sounds ?fluffy?) then it is too rich at the high end. Weaken the mixture by closing the high jet in increments of ¹/₁₆ of a turn. If the track temperature is high then turn the low jet out by equal amounts.

? If the top end fades or pops and spits then the mixture is too weak. Open the high jet in increments of ¹/₈ of a turn.

? If it has poor pulling at low revs coming out of corners, but no engine smoke is visible. The mixture is too weak at the low end. Open the low jet in increments of ¹/₈ of a turn.

2.4 Checking the mixture

After the engine has run then remove the cylinder head and check the top of the piston.

? Wet & oily indicates that the mixture is too rich (smokes a lot out of corners?),

? Dry & black indicates that the mixture is perfect,

? Dark Grey indicates that the mixture is a bit too lean,

? Light Grey indicates that the mixture is so weak that it may result in engine damage.

Always remove and replace the head with great care.

2.5 Setting Tick-over on Clutch Karts

Ensure that the carburettor is clean and serviceable, that the Pop-Off is correctly set and the jet screws are set to the initial settings .

You may find it easier to remove the Air Intake Box assembly complete with the Back-plate in order to gain access to the idle adjust screw. If you do you will need to put spacers in place off the back-plate (8mm Nylock nuts are ideal) in order to prevent the carburettor securing screws from ?bottoming?.

The chain and the back wheels need to be in place and free to rotate.

SAFETY - Ensure that the kart stand is steady and secure, that the wheels are clear to rotate, that there is nothing close to snag and that you keep well clear.

With the engine warm adjust the idle adjust screw until the rev counter shows between 4500 and 5000 rpm. If you do not have a rev counter then

? Pull the brake on lightly,

? Screw in the idle adjust screw in until the clutch just starts to bite,

? Back off a touch.

To test the setting: With the engine running depress the accelerator just enough to spin the back wheels. Release the accelerator and as soon as the revs have stabilised but with the wheels still spinning pull the brake hard on. The engine revs should not drop as the back wheels lock.

2.6 Throttle Cable

Ensure that the throttle cable is adjusted so that the throttle is fully open when the accelerator is down. Also ensure that when the accelerator is fully depressed the pedal stop screw prevents the cable and throttle shaft arm from being stressed.