Tom's correct and lets face it, the old two-cycle motorcar engines posed a fire hazard where it was hot and dry. USFS Fire Control Handbooks prior to about the 1970's had a short section concerning spark arrestors and speeders. You'll find railroad rules conformed to those spark arrestor rules, as well as for other track machinery. All the speeder clubs today require a suitable USFS approved spark arrestor on all cars no matter what the motor or the season. You'd be pretty hard pressed to find any news stories about speeders causing a fire but, I'll bet those crazy environmental organizations trying to shut you down will have their lawyers research two or three cases from the 1940's or 50's and bring it up in a letter or the next public meeting. Just put an approved spark arrestor on that A&MR speeder along with a muffler and you should be fine.....in the wet, rain and fog.
ARD