Tuning Your Rotax Engine
Tuning one's engine ensures a long and productive life for your vehicle. However, newbies might just simply not know where to start. A newbie myself, perhaps some of my newly discovered pointers could prove useful. What i have learnt is that owners of Rotax 125cc engines have to pay attention to 3 areas:
Regular cleaning and cleaning solutions
Be aware of the cleaning solutions used to clean parts of your engine, to prevent damage. Some components in the engine are made of rubber and are subceptible to damage to integrity if a harsh cleaning agent is used.
This image is of the power valve bellows which is a soft rubber component in the Rotax engine and can be damaged if cleaned with a harsh, corrosive cleaner. A result of using a damaged power valve bellows is a piston blow off.
Similarly, carburetor parts should only be cleaned with a carburetor cleaner and brakes should be cleaned with a fast evaporating brake cleaner. The importance of cleaning is in prolonging operating life, preventing foreign materials from damaging the engine, and it also helps when one has to identify problems with the engine.
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Carburetor
With most of the problems that i had with my rotax, i have received advice to check on the carburetor and make adjustments. The rotax engine carburetor uses a fixed jet system and jet changes are neccessary fof proper operation of the motor.
Many Rotax owners complain of a bog while turning, or when they release the throttle. The float will operate the needle & seat and if incorrectly adjusted, may cause a bog.
Follow these steps to set your float level correctly:- First remove the carburetor from the motor to access the floats.
- Invert the carburetor and remove the float bowl. Make a note of how the floats are positioned in the float bowl cavity.
- While still holding the carburetor upside down, check the float lever.
- Locate the prongs of the float lever. The prongs must be parallel with the base of the carburetor. If the prongs are not level, you adjust the prongs by bending the small flap that sits on top of the needle and seat. Bend this flap until the float prongs are level. Be sure that you don;t bend the prongs itself.
Now that you have adjusted the floats to their proper position, we need to set the clip appropriately.- Begin by adjusting the slide needle to its richest point. You do this by removing the small 'e' clip and setting it at the lowest groove on the slide needle.
- As you move the clip lower on the slide needle, it raises the height that the needle sits at in its resting position. This allows more fuel to enter the carburetor, thus making the system 'richer'. If you were to raise the clip to a higher groove, this would allow less fuel to enter and thereby create a 'leaner' condition.
- Next you will need to install the proper Main Jet for the current conditions. The proper main jet can only be determined taking into consideration these conditions:
- Temperature
- Humidity
- Barometric Pressure
- Altitude
- After the Main Jet is installed and the carburetor is reassembled, you replace it on the motor tighten the hose clamps and ensure that all of the bolts are tight too.
- Run the kart out on the track and observe proper 'warm-up' procedures. Once the engine is warmed up, begin pushing it to its limits.
- LOW RPM TUNING - If the kart runs rough at lower RPM's (5,500 - 8,500), we must adjust the needle setting to be 'leaner'. How 'rough' it is running should determine this adjustment. Never adjust in excess of (2) grooves in any direction, as this might lead to a low RPM seizure.
- HIGH RPM TUNING - If the motor won't cleanly rev from 10,000 RPM to 12,500 then change the main jet to (1) jet lower. I.e, if you are running a 168 jet and the motor pulls cleanly through to 11,500 but begins to break up or bog at 12,000 you might consider changing to a 165 main jet. If the leaner jet improves the situation, but still doesn't seem totally right, check your plug reading to ascertain if a leaner jet is suitable. BE EXTREMELY CAUTIOUS. At this point, going too lean could result in an engine seizure. Once you have found the appropriate main jet, it is possible you might have to change the clip setting to eliminate any lower RPM bog.
If the 'leaner' jet does not rectify the problem, you should install a jet that is one size bigger and thus richer.
A loud 'popping,' or a sudden drop off in performance at high RPM can mean that the jet is too lean.
At any time when the jet seems too lean you stop your go kart immediately, you should adjust to get a good 'cut' on the plug and reading on your plug indicators.
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Electrical
Many Rotax owners remain unaware of the importantance of the electrical system to proper operation of their kart. The Rotax operates uses a 'total loss' ignition system which, means that there is no on-board charging system, and that the ignition system relies solely on the battery for power to supply the ignition coil. This means that if the battery does not have adequate power, the ignition coil will not function properly. As a result, it is VERY important that you ALWAYS keep your battery at full charge and have some spares.
The commonly used battery is a sealed lead-acid battery. It is not a Ni-Cad, nor is it a Nickel Mh battery. As such, it needs to be charged like any other lead-acid battery. This battery does not have the type of memory that is associated with the Ni-Cad or Ni-Mh. If the battery is ever fully discharged there is a good chance that it will be damaged. The damage may not even be apparent immediately, but the lifespan of the battery may shorten significantly.
You should avoid jarring the battery unnecessarily, or dropping it as either of these can dislodge the internal components and cause a short circuit. The battery should be placed on the approved charger anytime that it is not being used until about two to three hours beyond the green light illuminating. Due to its nature, it is advisable to have at least one spare battery that is fully charged. This is probably the quickest and easiest item to change on the kart, and should be your first adjustment in any situation where the ignition seems to suddenly cut-out or misbehave.
