Unlike a car that runs relatively normal with a dirty air filter, operating a dirt bike or ATV using a clogged lung poses a number of problems.
In fact, you might not even get the engine to start if it's completely gummed up.
Dirt bike and ATV air filters work really well mostly thanks to the applied thin layer of oil that traps the finest of particles from getting inside the engine while maintaining air flow. It's also this effectiveness as well as the oil barrier that turns a clean air filter into a dirty one often after just one ride. Dirt bike and ATV air filters are typically made from foam rather than paper, like those found in cars. The air filter is coated in air filter oil though motor oil could be used if you're desperate but it doesn't distribute around the filter as well.
Eventually, a dirty filter prevents air from getting into the engine which usually causes a rich fuel setting. Therefore, that black smoke blowing out the exhaust pipe is one sign of a clogged air filter. It's easier to spot on a carbureted engine because fuel injected bikes with advanced EFI and ignition systems have the ability to compensate for the clogged filter. On 2-strokes, it may resemble a foul spark plug or too much oil in your premix.
Other signs of a clogged air filter include:
- Hard starts
- Engine stalling
- Sluggish response
If the engine fails to start then you've completely neglected the air filter because air can't get in. Most if not all riders avoid this even if the bike is overdue for a filter change.
The symptoms of a dirty air filter mimic more problematic issues so if your dirt bike or ATV exhibit any of the above it's a good idea to check the air filter first to save you time and possibly money from going down unnecessary rabbit holes as you ascertain the problem. It's an easy fix and perhaps serves as a reminder to check it more often.
Another complication from a dirty air filter is passing dirt and debris into the engine. Eventually, the muck sticking to the filter builds up and breaks off with only one place to go. You won't experience any signs of this until it's too late. If you haven't ridden too many miles with a dirty air filter the engine oil acts as secondary protection by trapping the dirt. By now though you've got a growing mess and you'll need to change the air filter, engine oil and oil filter.
Changing the air filter is almost as routine as changing the oil so unless you've completely forgotten it's unlikely you'll ever encounter these problems. For tips on cleaning the air filter read How To Clean a Dirt Bike or ATV Air Filter.