how to install gas probes

Many articles have been written about performance. The add-on components that squeeze the motor and spin the track can only mean two things: bigger grins and a quicker ride.

Let's take the add-on, two-stroke tuned exhaust system, for example.This system is designed to raise the motor's horsepower figure by increasing the efficiency of the air and fuel charge taken into the combustion chamber.Once the charge is pulled in, the tuned exhaust continues its purpose byhelping the motor burn and discharge the spent air and fuel mixture in amore efficient manner. Horsepower characteristics are changed.

There is more to increasing performance than slapping on a set of twin or triple tuners. Reclutching and rejetting are required. Why? Well, when an engine's horsepower characteristics are changed, clutching and carburetorjetting should also be changed to ensure a proper match. Failure to do so usually results in a performance loss, since engine power will not be transmitted to the track efficiently.

Additionally, improper jetting for elevation, ambient temperature, fuel type, rider weight and snow conditions can cause engine damage. Keep in mind that most aftermarket manufacturers supply jetting and clutching information for your particular sled.

The remainder of this article will discuss the benefits and the installation process for exhaust gas temperature (EGT) gauges and probes.

You may be wondering how an EGT gauge can help a tuner design proper carburetor jetting. It's quite simple.

Exhaust gas temperatures are directly related to how lean or rich an air/fuel mixture is. If more fuel is added to the air/fuel mixture (known as richening), exhaust gas temperatures drop. If fuel input is reduced,(known as leaning), exhaust gas temperatures rise.

An overly rich mixture will cause horsepower loss and spark plug fouling. Profound lean mixtures cause extreme heat in the combustion chamber. This ultimately leads to horsepower loss and usually engine burn-down. Knowing how rich or lean your air/fuel mixture is will help determine how much to change jetting to safely gain optimum performance.

The snowmobile chosen for the installation was a 1998 Polaris 700 RMK.Jerry Mathews of Starting Line Products assisted. Two single readout Westach EGT gauges with SLP high speed probes were chosen. These gauges come in single, twin or triple readout faces.

1. With a pen or small punch, mark where the EGT gauge accessory pod will be mounted. In this case, above the stock tachometer/speedometer instrument pod.

2. Drill out the mounting holes with the appropriate sized drillbit.

3. Install the gauges inside the pod. Secure the gauges with mounting bracket and bolts. Do not over-tighten the instrument mounting bracket.

4. Remove the EGT gauge back-lighting cover and insert a back-lighting bulb. Replace the cover.

5. Drill an 11/64-inch hole in both pipes within 6 to 8 inchesfrom where the exhaust flange bolts to the cylinder, depending on the engine and pipes you have. The holes must be at the same distance in each pipe and parallel to each other. SLP recommends a probe placement of 6.5 inches from the cylinder.

6. Connect the wires from the probe to the EGT gauge. Ensure the wire routing matches the schematic drawing.

7. To test the EGT gauge and verify wire connection is correct,light a propane torch and heat probe end. If connections are correct, the gauge will respond. If nothing happens, reverse the wire connections and repeat this step.

8. Place the probe inside the pipe with a small amount of high temperature silicone. Tighten the probe mounting clamp.

9. Do not alter the shielded probe cable length. However, the pigtail wire between the probe cable and the gauge can be lengthened with matching gauge wire. The EGT head is calibrated to receive its "signal"from the probe based on a predetermined cable length.

Note: Altering the length will adversely affect the signal the probes ends. Also, do not let the probe cables contact the spark plug wires orplug caps, as an electrical interference may occur causing an incorrect gauge reading.

10. Thread the probe cable through a routing channel of your choice.

Now that the EGT gauge(s) have been installed, the snowmobile's tuning (jetting) can be confirmed.

Start and warm up the motor for about two minutes. Begin the test by throttling up to 1/8 position for 30 seconds. Increase throttle position to 1/4 throttle and hold for 30 more seconds. Continue at 30 second intervalsand increase throttle position up to 1/2, 3/4, and finally to full.

Temperatures with proper jetting should be:

1/8: 800-900 degrees F

1/4: 900-1,000 degrees F

1/2: 1,000-1,100 degrees F

3/4: 1,100-1,150 degrees F

full throttle: approximately 1,200 to 1,300 degrees F

Note: temperatures will vary depending on engine design

For more information about EGT gauge kits, contact: EGT · 714/997-5224· www.exhaustgas.com