SPARK PLUG GAP
If you are experiencing any slight misfiring of the engine the factory suggests that a plug gap of 0.5 mm to 0.6 mm should be tried.
TEMPERATURE GAUGES
H20TEMP and RPM gauges specific to the Rotax Package are available. The water temperature gauge utilizes a pre-threaded, machined piece that every FR125 motor comes pre-drilled for. This piece is highly recommended to assist in your tuning efforts. When fitting a water temperature gauge it is very important that it is not connected directly into the wiring loom as this will instantly effect the power into the ignition / coil causing loss of power and effecting the performance of the engine. The correct fitting procedure is to connect the wiring from the temperature gauge directly to the battery or the starter button. KRM offers a unit available from Alfano that is specific to the Rotax package.
RUNNING IN COLD WEATHER
When the engine is used in colder temperatures (below 10° C (or 50° F), using the standard 168 main jet causes the engine to run leaner. From this a higher piston temperature appears due to hotter combustion causing the piston to become hotter and increase in diameter. Due to cold outside temperatures, the engine might not reach the recommended minimum coolant temperature of 45°C or 113°F. In this case, the cylinder diameter will be less increased compared to the diameter of the piston.
Due to the above, the piston-cylinder clearance might be at the lower end of the tolerance and increases the risk of piston seizures!
If the engine is not being run in according to the instructions, possibly not letting the engine reach the minimum required coolant temperature and going over the recommended rpm limit, could also lead to an engine seizure. It's also very difficult to follow the instructions without using a rev-counter and temperature gauge.
To avoid these failures, take the following precautions:
1. Make sure you follow the run in procedure before. The proper way to warm up the engine is to run it on the racetrack - not on the stand! (Engine heats up faster if operated under load!)
2. Make sure you change the size of the main jet in the carburetor according to the outside conditions (temperature and altitude). Refer to the jet chart clearly shown on page 16 of the Australian Rotax owners manual for the correct jet size. Please also consider the altitude of the racetrack when you take the main jet size from the chart.
3. Make sure that engine reaches it's minimum coolant temperature of 45°C or 113° F, if not, the radiator needs to be covered accordingly.
IGNITION TUNING
The one item that we have no solution for is the advance curve. Here you will experience a drop off in power at 12500 RPM . If your jetting, plug and gearing are properly selected the effect is considerably decreased. You may also note popping in the exhaust use an iridium plug.
MIKUNI FUEL PUMP
Placement of the fuel pump is on the airbox bracket- this is a tech item. On occasion, the fuel pump will contribute to popping as well as no power on long straight. The confusing factor is that if your main jet is rich, the engine will not rev out, it can be thought to be the pump. To insure that the pump works to the maximum fuel flow, one must reduce any pulse losses from the crank case. The crank case pressure is transferred to the pump diaphragm via a pulse plastic line, the length of the line and the elasticity of the line will detract from the energy on the diaphragm to displace fuel from the tank to the carburetor. Use a rigid plastic line and make the length as short as possible. This is to provide the least resistance to the pulse energy. It is also a good idea to use a low-resistance fuel filter.
What does the power valve do?
The device varies the exhaust port timing. In lower RPMs, the exhaust port is lowered retaining the burning gasses for a longer period, producing more gas pressure on the piston hence providing more torque. In the high rpm region the exhaust port is raised allowing the engine to produce more horsepower. Inlet port and exhaust port positions is what controls the maximum rpm that an engine can obtain. You will feel a difference when this motor "comes on the power"!
With this engine, the manufacturer provides a system consisting of a gas bellow connected to the exhaust port allowing gas pressure to build up inside the bellow expanding the bellow against a spring. The bellow is connected to a slide device that raises or lowers the exhaust port. The opening of the slide is proportional to the gas pressure in the exhaust port this is dependent on engine load and rpm.
You can have a situation that the engine is sustaining a large load at low rpm's this produces high gas pressure in the port raising the valve prematurely, robbing you of the required torque. Other manufacturers use electronic control, where a computer makes the decision based on load and rpm's. In reality after carefully looking at the curves provided by Rotax on this engine, one realizes that there exists a large overlap band where the above problem is not noticeable in the type of application the engine is subjected to.
If one must have a tweak with the power valve, only ever turn the red adjuster clockwise increasing spring pressure, this will retard the opening of the valve with respect to engine rpm's. You may have a situation on a circuit where a set of corners will force you to operate at low rpm's for a long period of time, creating high gas pressure in the port, this could cause the valve to open robbing you from the required torque. In most other situation the factory setting will work very well.
Maintenance of the device.
The bellow will build up with oil as you operate the engine, the danger here is that if sufficient oil is retained inside the bellow this can block the gas hole, gas pressure can expand the bellow raising the valve but when the oil blocks the hole the spring pushing against the bellow is not strong enough to clear the oil hence the valve remains open, robbing you of down low torque. Thus after every heat or at least after every meeting dismantle the bellow and clean out the oil.
Common Mistakes-Courtesy of Ross Lee
Some common mistakes that many Rotax Max drivers experienced:
1.Engine performs poorly due to dirty carb. These steps are to check and remedy: (a) use screw drivers that perfectly fits your jets; mismatched tools will damage the delicate components (b) clean external surface of the carb (c) disassemble the 3 jets and inspect for clogged jet holes by holding up to the light. Determine if the jet is too clogged, then (d) use pressurized air from air pump to blow the jets. Use the brake cleaner first followed by pressurized air. NEVER use pressurized air from air pump directly on the carb!!! This common mistake could cause damage to the carb. Use brake cleaner to clean the carb instead. However, pressurized air may be used on the jets when disassembling from the carb.
2.Engine performs poorly when leaving the corner. First, check the coil grounding. Not grounding the wire to the engine or if ground wire is broken or loose, loss of power will result in insufficient spark to the ignition.
3.Engine performs poorly due to low or faulty battery. This is a common problem - the battery is not fully charged or losing voltage. Sometimes the battery is damaged by using quick-charger (not the standard equipment supplied with the engine) or through continuous vibrations. Please note the battery is gel-type thus charging with high-current will cause severe burning. Also, if foam is not placed under the battery, excessive vibrations will damage the gel and electrodes.
4.Engine can not start: malfunctioning starter. Another common occurrence is no response from the starter button. In this case: (1) check if the power comes through the starter switch. (2) Tap the starter with a metallic instrument, this sometimes works. This is only a TEMPORARY quick-fix. A better solution would be to disassemble the starter set and refit with the 800 Baht starter repair kit. No need to pay 6,800 Baht for a new starter!
Please note the carbon brush inside the failed starter may have burnt-out due to excessive depressing of the starter button (longer than 5 seconds at a time).
4.Difficulty in starting the engine. The correct way to start Rotax Max engine after taking fuel hose off/no fuel in the fuel line is to:
(1) Blow the line so fuel can enter the carb. Or, take off the air box, pull carb choke and depress the starter for 5 seconds (with ignition OFF). Conduct each start attempt with one hand over the carb inlet while pressing throttle to full-open position. This is to create suction force for the fuel. If you do not feel the fuel on your hand, repeat this process every 10 seconds until your hand is soaked in fuel.
(2) With your hand off the carb inlet, depress the starter button again, with the ignition switched ON. Depress the starter for 5 seconds with 20% open throttle.
(3) If not successful, wait another 10 seconds, repeat step (2) until the engine starts.
(4) Close the carb's choke and accelerate (not too high rpm) until the engine response is ok.
(5) Place the air box on the carb. Try to start again on the stand and check engine response is ok.
Note: Depressing the starter button for an extended time, damage to (a) the battery and (b) the starter can occur. The gel type battery is not designed to draw high power for extended periods. This will burn the gel element and shorten the battery life.
The starter is also designed for a starting function only (interval operations). Depressing the starter button for extended time will cause the carbon brush to overheat and battery life will be shortened. This tip is from Rotax (International). Follow this tip for longer starter and battery life
5.Engine lacks power at mid- and high- RPM: Check your exhaust valve. The bellow may be released or difficult to move if tar/residual from caster-based oil is present. Rotax (International) recommends using good quality fully-synthetic oil ex: Shell Racing X (not Racing M). Shell Racing X provides a cleaner burn, less
If the exhaust valve can move freely, check if it can fully open as well. The stud of exhaust valve has 2 different lengths: the short one is at the metal exhaust blade and the longer one is at the black plastic valve.
6.Too lean mixture: The engine rev's at a high RPM but does not demonstrate a strong pull. This may be due to insufficiently SMALL mainjet, which creates a lean condition. Another indicator of being too lean is the engine
