By having your dad put the air resistor on didnt add anything really filter-wise. That part is 100% for blocking any flame that might backfire out of the carb... which is why it is usually referred to as a flame arrestor in the marine industry. Many race-boats.. such as Opel, Eliminator, etc.. don't even run the flame arrestor sometimes. The reason for this is that there is really no dirt particles on the water. The arrestor will stop LARGE objects from entering the engine.. like a bug or something.. but by having him put it back on while working on it at the house didnt really matter. Course.. ive had it backfire out of the carb when timing the 351 in my old 77 SeaRay.. lol luckily i had the arrestor on tho.. nothing but smoke came out of it lol.

As far as nitro engines go, always run with an air-filter to be safe. When im in the garage messing with it on the stand, i sometime's won't. If you start running it around however, definately stick it on there. People sometimes get a little too panicky about running without a filter. Its perfectly fine if your in a clean envionment.. such as on a 1:1 car in driveway timing it or something, or your nitro car on its stand while tuning. The problem comes when people run it around on the street or in the dirt where it can suck in dirt and whatnot. If your street was good and clean and you did it for only a short while, I wouldn't worry about it at all.