Rotax Maintenance


The last thing that you need is unreliability when you arrive at the circuit. For this reason I thought it would be a good idea to devote this column to Rotax Maintenance and checks.

Hopefully the battery has been stored in a charged condition, the regular lead acid battery that is supplied with engines is the Yuasa. These have proved to be very reliable. If the budget is not too tight a spare battery is always a good item to have to hand. If a battery has been left for months in a discharged state it may never recover to its former strength.Low cost equivalent batteries are not an option. The Rotax Yuasa battery shared its dimensions with very inexpensive other brands. These cheaper units are in fact designed for alarm systems and are not shock protected. While the Rotax battery is not a true Lead acid Gel type it does have shock protection between the plates.

This material absorbs the acid and protects the plates from contact with each other. The gear oil should be drained and replaced. With the old style clutch the engine will almost certainly have plastic balance gears. These should have a maximum fill level of 50cc. The late and current type of steel gears should have a maximum fill of 100cc. There is a Rotax approved and supplied gear oil. Alternatively a good quality light gear oil will do it. The next step to happy days is to clean and check the wiring loom. I think it is probably best to remove this from the kart and give it a really good wash. The most important tiny item, often overlooked is the red rubber seal that fits inside the multi-plug connector that attaches to the bottom of the coil. If you are using a coil extension bracket, there are a couple of words of warning. Firstly you need to be sure that the loom is not too stretched from the ignition pick up on the back of the crankcase up to the multi-plug on the coil.

Some of these brackets are just a bit too long so it is worth making sure that their adjustment allows for the loom to be safely attached. It is also imperative that the thick black earth wire from the loom is attached to the engine and not remotely so that all of the earth has to travel through the short earth strap which bridges the coil mounting rubbers. The condition of this earth strap should be carefully checked and replaced if in any doubt. Poor or incorrect connection here can lead to misfires, bad performance and at worst, destruction of the coil itself. A final word of warning in this area is that there is a temptation to shorten the HT plug lead when a coil extension bracket is fitted, this is not allowed within the regulations; there is a minimum length. While in the area of the spark plug, remove it clean it carefully (brake cleaner works well) and connect it to the HT lead. It is easy to check that you have a spark by resting the plug on the cylinder head and cranking the engine.

The way the wiring loom is constructed allows the engine to crank without the ignition on/off switched on. Before making this check be sure that there is no risk of fuel igniting when the plug sparks! The switches can be a source of trouble but this is rare. If the above check is successful then it is clear that all is well. A common mistake is incorrect wiring to the switches. All wires to the switches are on the + or positive side of the loom, there are no negative or earth connections there to confuse you. The thick wires always go to the start button and the thin wire always go to the on/off switch. On more recent looms one of the thin wires is “piggy-backed” off the thick live supply wire, always be sure that this thick wire is connected to the start button. Assuming that the switches are in good order you should now be able to crank the engine over with the spark plug out. Again it is a good idea to ensure that the wiring isn’t tight and pulling on the switch connectors. This is the most common cause of switch problems. Often overlooked is the fuel pick up in the petrol tank.

This is a regular length of fuel pipe with a brass weight or filter on the bottom end. The length and flexibility of this hose is of great importance. The brass weight should sweep the bottom of the tank and the flexibility of the hose will allow it to follow the fuel as the centrifugal force moves it around in the corners. Fuel starvation can be a really difficult fault to diagnose. The carb is very simple, but you do need to know what you’re doing to keep it in good order. If you want to do your own service work, you will need some special tools and a spotlessly clean environment to do it in. I was lucky to be taught how to work on carburettors when I was at school and a lot of that instruction still helps me every day. If in doubt the Carb is something that you should entrust to your friendly local Rotax Service Centre..