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Old 08-13-2008, 10:41 AM   #1
Marc Miller
Birel & Rotax Specialist
Join Date: Jan 2008
Posts: 850

>>>>>>>>>>>> TUNING
LOW RPM TUNING - If the kart runs rough at lower RPM's (5,500 - 8,500), we need to adjust the needle setting to be 'leaner'. How 'rough' it is running should determine this adjustment. Never adjust more than (2) grooves in any direction, this can cause a low RPM seizure.

HIGH RPM TUNING - If the motor will not rev cleanly from 10,000 RPM through to 12,500 then change the main jet to ONE jet lower. For example, if you are running a 168 jet and the motor pulls well through 11,500 and begins to break up or bog at 12,000 you should change to a 165 main jet. If the leaner jet seems to help, but still does not feel 100% right, consult your plug reading to determine if a leaner jet is suitable. BE VERY CAREFUL. At this point, going too lean could cause an engine seizure. Once you have found the appropriate main jet, it is possible you may have to change the clip setting to eliminate any lower RPM bog.

If the 'leaner' jet does not remedy the problem, you should install a jet that is one size bigger (richer).
The indications of a jet that is too lean can include a loud 'popping,' or a sudden drop off in performance at high RPM.
Any time the jet seems too lean you should consider immediately coming in to the pits, getting a good 'cut' on the plug and reading your plug indicators.

>>>>>>>>>>>> Electrical / Battery
Too many Rotaxians are not aware just how important the electrical system is to proper operation of their kart. The Rotax FR125 operates using at 'total loss' ignition system. This 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 also 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.

The FIAMM GS 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.

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. Because of the nature of the beast, it is very 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.

>>>>>>>>>>>> Summary
The Rotax FR125 has proven to be a low-maintenance, high performance and reliable racing engine. The caveat to that statement is that low-maintenance does not mean no maintenance. Follow the above procedures, with special care to the carburetor, power valve, air filter, and electrical system, and the Rotax will continue to offer you one of the best values in high performance karting powerplants.
Marc Miller
Director of Brand Development
MRP Motorsport/Birel
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