Lots of riders are asking about spark arrestors for their Trials machine. Spark arrestors are required on all USFS and BLM lands and as responsible riders we all should have a spark arrestor on our bike when the fire danger is possible.
A spark arrestor is basically a screen being placed over the exhaust of our bike that will stop any spark large enough to start a fire from blowing out the back of a hot exhaust system.
While the screen stops sparks it also stops other partials from passing through the exhaust system such as small amounts of oil that stick and build up rather quickly on the screen.
When you use a spark arrestor be sure to take it off and clean it after each days ride using carb cleaner a small brush and/or scraper to remove as much residue from the screen as possible. Running a dirty spark arrestor is like you running up a hill with a rag over your mouth, the dirtier the rag the harder it is for you to breath and get up that hill. I have attached a couple of pictures of an arrestor i took off of a bike, notice how dirty the screen is and the pile of burn oil and other junk that fell off of the arrestor when i removed it from the bike.
The other picture shows oil blowing out of the exhaust system onto the swing arm as the bike tries desperately to breath with the exhaust exit plugged with a dirty spark arrestor. Thumbs Up Trials carries several styles of spark arrestors. Elrod Machine in Flagstaff Arizona is working on a new design that looks like it will be a very breathable design that is easy to service and clean after each ride.