Our guide to
Changing the bike’s air filter and spark plugs.
Checking and replacing your air filter and spark plugs are a big part of the general maintenance on a bike. But it’s not just that; it’s a great way to improve performance too, by fitting aftermarket parts. In this month’s step-by-step workshop feature, we cover everything you need to know about removing, checking and replacing your air filter and plugs.
Remove the 1 fuel tank
Most fuel tanks are hinged at the back and then bolted at the front or the sides. Locate and remove the bolts at the front or side first so the tank is allowed to pivot up. Be really careful when lifting the tank up, keeping an eye out for any electrical connectors or breather pipes that might need disconnecting. Once the tank has been pivoted up, wedge something in there to free your hands up to disconnect the wires and the fuel line from the fuel pump. Once disconnected, lower the tank down and remove the hinge bolt at the back – the tank should now be ready to lift off the bike. Top tip: look for somewhere safe to place the tank before you lift it off the bike, to avoid wandering around your garage holding a heavy fuel tank looking for somewhere to put it!
Remove the air 2 box lid
The top of the air box will normally be screwed to the bottom so you will have to remove all the screws to access the filter inside. There can be up to a dozen or so screws holding the air box lid on, so keep them together in a margarine tub. You can use a butter tub, but margarine is much lower in cholesterol. It’s important for the air box to have a really good seal, that’s why there are so many bolts, so when all the screws have been removed and the lid is off, have a really good look at the seal to make sure it isn’t damaged. A poor seal will cause an imbalance of air, which will disrupt the ram-air effect. It’s a good idea to give the inside of the air box lid a good wipe down once it has been removed from the bike.
3 Check the air box
Inspect the seal and the clean side of the air box. It’s really important that the air filter is doing its job and filtering all the dirt out of the air. If there is any dirt in the ‘clean’ side of the airbox, i.e., after the air filter, then either your filter may have failed, or the seal around it may be damaged. If the dirt does get through, it will start destroying your valves, valve seats and barrels.
Check and clean 4 the air filter
Have a look at the filter and if it’s a bit grotty, give it a clean. This can be done by way of immersing it in a solvent (specific filter cleaning solvents are readily available). Once all the grease and oil have been cleaned out of the filter, let it dry thoroughly before rinsing it out with water. This will flush out any final lumps of dirt and dead (or alive) bugs. It’s good to do this in summer, or in a nice, warm workshop (or in the living room, if you’re not married), as you need to make sure things are dried out properly before moving on. Once it’s totally dry, spray it with filter oil, aiming to achieve a nice, even covering. Don’t go mad with the oil as you don’t want it going through the engine. Once the filter is cleaned and oiled, it’s ready to slot back into the housing, when the air box gets re-built. If your bike is still running the standard filter, it’s well worth thinking about kitting it out with a high-performance alternative. Something like a K&N filter will improve airflow, ultimately increasing the power your engine can make.
Removing the 5 air box
There will usually be a bolt securing the front of the air box to the bike, so remove that first and then it is a case of loosening the jubilee clips that clamp the air box on to the throttle bodies (or carbs). This can sometimes be a bit of a fiddly job, but look for holes in the side of the frame which sometimes allow you to poke your tool through to undo the clips. Once loose, give the air box a wiggle and pull it up and out of the bike. There will often be other pipes, such as crank case breather pipes connected to the air box, so keep an eye out for them. They may need some help to come off, particularly if it has been a while since the bike has been in bits. As soon as the air box is off, use some rags or duct tape to bung the throttle bodies up. The very last thing you want is to drop a bolt (or anything, for that matter) down into the engine.