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Old 08-13-2008, 10:39 AM   #1
Marc Miller
Birel & Rotax Specialist
Join Date: Jan 2008
Posts: 850
Default Rotax TECH: Cleaning & Carb Basics

>>>>>>>>>>>> Cleaning
The cleaner you keep everything on your Rotax, the easier it will be to diagnose problems and rectify them. Keep in mind you want to use appropriate cleaners for certain parts though.

1. POWER VALVE - The power valve bellows is made of a pliable rubber. The condition of the rubber itself plays an important part in the proper operation of the valve. Cleaning the bellow with an aggressive cleaner, such as Simple Green, could weaken the rubber and cause it to "blow off" the piston a lot easier. Thus, we recommend using only mild soap and water for cleaning the bellows.

2. CARBURETOR - When cleaning the carburetor parts, i.e., jets, floats, filters, etc., you should use a carburetor cleaner. To clean any brake component you should use a good quality, fast evaporating brake cleaner. All of these items are really common sense, but most of the time, problems could have been prevented with proper cleaning to begin with. NEVER STORE YOUR ROTAX CARB WITHOUT DRAINING ALL FUEL COMPLETELY OUT.

3. AIR FILTER Do you want to gain a few tenths? Have you not changed or cleaned your air filter? A clean air filter makes a marked difference in performance. We recommend you only use SOAP and WATER on the Air Filter. Gasonline or degreasing / cleaning agents will distort the shape and integrity of the air filter.

4. CLUTCH DRUM You would be amazed the amount of small pebbles, oil, grease, etc. that can lodge themselves in the internal side of the clutch drum. It is recommended to clean the clutch drum with brake parts cleaner after every race. This will help maintain the life of your clutch shoes and maintain optimum performance levels.

>>>>>>>>>>>> Carburetor Basics
The Rotax Carburetor, the Dellorto VHSB 34 QD uses a "fixed" jet system, jet changes are necessary on a daily basis (sometimes hourly) and in a lot of cases those changes are critical to the proper operation of the motor. Drivers often complain of a bog during turns, or after letting off the throttle. The float will operate the needle & seat and if incorrectly adjusted, can cause a seemingly untraceable bog. The first step is to ensure the needle and seat of the carb are clean. The second step is to ensure the floats are set correctly.

To correctly set your float levels do the following:
You must remove the carburetor from the motor to gain access to the floats.
Turn the carburetor upside down and remove the float bowl. Make a note of how the floats (white plastic pieces) are positioned in the float bowl cavity.
Continuing to hold the carburetor upside down, examine the float lever.
The prongs of the float lever should be parallel with the base of the carburetor. If the prongs are not level, DO NOT BEND THEM!!! 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 absolutely level.

Now that you have adjusted the floats to their proper position, we need to set the clip appropriately. To begin, set the slide needle at its richest point. This is done by removing the small 'e' clip and setting it at the lowest groove on the slide needle.

NOTE: Visualize this: 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 it is making the system 'richer'. Conversely, 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 tune the carburetor for current conditions.

Take the kart out on the track and observe proper 'warm-up' procedures. Once the engine is warmed up, begin pushing it to its limits.

>>>>>>>>>>>> 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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