1978 250 wr/or, Spark Arrestor Question

I'm hoping someone can answer some basic questions regarding the spark arrestor on my bike. The '78 parts list shows a different muffler/arrestor than what I have. I think what I have is from a later year (1979-1981/2?). It is stamped #F15-1041 on the plate.

First, what is the big spring that's welded inside the arrestor for (see pic)? I assume at one time there were muffler packing "cartridges" that were available that were loaded in and held by the compressed spring. Is that correct? To pack the muffler I'm just going to wrap fiberglass sheet several times around the perforated core tube attached to the end cap and then use wire to tie it tightly to the tube. Any reason not to do it that way? I need to do something because this bike is real noisy as is.

Second, this arrestor doesn't seem to have a screen. I believe the units for US bikes had a screen inside the end cap. This one doesn't. Has anyone added a screen to this type of arrestor? Is there a retrofit of some kind that anyone can recommend?

Thanks, and if this post should be in another forum let me know.

I had the same problem with my 79 OR 250. The spring was stuck in the tube and I ended up soaking it for a week in a concentrated soap solution to dissolve the carbon gunk.... it finally came apart. Mine had some screen in the front end, not the cap, but I'm not sure it was originally that way from the factory. I also wrapped the packing around the tube, then slowly stuffed it back into the canister.
Hope this helps, good luck!
W

Woodman, my 79 wr 250 had the same one as yours. the little screen was missing and the big spring came out too. I just used the fiberglass in a little bag from lowes and just wrapped it with out tying any thing to hold it on. Then just slide it back in and poke some more down around the sides. I made a small cone that I can install when needed for certain races and then I can take it out if I want.

That's a pretty looking rod, you buy that new somewhere?

Yup, the last from huskydoggg for me.