I love to race motocross, there's no doubt about it. I'm sure you think the same if you've tried it. But if there's one thing I hate the most, it would probably be a broken bike on race-day. I try to keep up on maintenance as best I can so that my dirt bikes won't fail when I'm on for a ride or on the day of a race. There are many things you should do in order to prepare you dirt bike for a motocross race, so I'm going to tell you how.
They May Be Called "Dirt" Bikes, BUT.....
First of all, is your bike clean? You should never put away your bike dirty. Although I hate to admit it, I do not achieve this goal just because I can't at times (getting back extremely late at night, not having a pressure washer, etc.). But it's very important that you keep your bike clean. It will make everything last much longer, and working on the bike will be easier when you have to do maintenance on it.
Okay next question.... When's the last time you changed oil and filter? It depends on your bike, but you should change oil every couple of races, or every 5-10 hours if you ride in between. Oil filters should be replaced every other/second time you change the oil. Many riders make the mistake of not changing the oil often enough, and this results in seizing of the engine. A big NO-NO, especially for four-stroke motocross bikes. If they even run low on oil, the cam(s) might not get enough lubrication, causing them to score and possibly seize. And if one thing goes out on them, often it will destroy more parts. So don't forget to do you oil change intervals!!!
Next on the list is your air filter. Another crucial part of maintaining your dirt bike that many riders neglect doing. Cleaning or changing an air filter is easy, and cheap, so there's no excuse for not doing it. Hardcore riders often clean it every ride, but that isn't necessary if you aren't riding in sand or mud. Clean it every 3-5 hours or so and you should be good. Your engine will last much long if it's sucking clean air going to it instead of dirt. Make sense?
Cleaning and tightening your chain the day before will save you a headache. Not only will this help prevent the chain from falling off or breaking, it will save you time if you're in a hurry on race-day.
Tires can help you win a race. If it's cracked or worn out then it's time for a new tire! Tire pressure is also very important for racing. Although you'll probably have to check/change it throughout the day, it's good to pump them up to 15 psi the night before. A good pressure for soft terrain is about 10-12 psi, and hard-pack about 13-15 lbs.
There are many fluid lines on a dirt bike, so remember to check those for cracks, wear, and tighten them if they're loose. These include lines for gas, coolant, brake fluid, and clutch if you have a hydraulic clutch. Top them off and/or flush them if they need it (I'll show you how to flush fluid lines in a future article/video). Also, check your brake pads to make sure they aren't worn out. You don't want to start racing and all of the sudden you have no brakes.
Check your clutch and throttle cables for wear. If they are starting to fray, replace them. I also recommend you to lube your cables every few rides just to help prevent them from seizing up.
A fouled spark plug can end your day like that. Or, it can hold you back just one moto/practice if you are smart enough. If you haven't changed plugs in a while, you may want to check what it looks like and possibly replace it. You never know when it could go out, especially if you're jetting isn't spot-on. Always remember to bring a spare plug or three; 2-stroke motocross bikes sometimes eat through them quickly.
Nuts and bolts keep your bike together. I know I didn't have to say that, but it's often disregarded when maintaining a bike. Remember to check and tighten any nuts or bolts that are loose. Common areas that become loose after use are: plastics, handlebars, forks, pipe, radiators, fluid line clamps, etc. This should be done before every race so that your bike doesn't fall apart!
Last but not least, don't forget to use fresh gas!!! I am a living example of this, but in my terms it was a little more extreme. I had a riding accident late August this year (2010) and hurt my shoulder, so I was out for about two months of any real riding. Well when I went riding at the end of October, I took my 125 out out for a good ride on a sand track. After an hour or less of riding the bike it stalled and couldn't get it started. I found it it was bad gas, causing it to score the piston and cylinder.
The reason I say this case is a little more extreme is because I have to to a mix of race gas and pump gas, mixed with castor oil; all of which don't last very long, especially when mixed together. So the best thing to do is buy gas the day before, and wait to mix it (if you use additives or 2-stroke oil) until race-day.
That should pretty much do it. If you do all of these things, there will be very little chance your bike will break down. Good luck, and ride safe!