Hi mick - it's me. I have done all work on my bike myself up until the carb work (too scared for some reason, though don't think bike store got it right so will have to do it anyway - bang goes $80).

anyway - it looked "virgin" to me (still had old screws for instance) but mechanic said it had been got @. he did not touch spacer just the main jet so that may be route I have to go to get rid of occasional back fire.

I know folk on site say big singles back fire a bit but every other one (both of them - a road bike & an enduro) I've ever owned never did. nor did the Savage, even after the K & N - the muffler did it. Lancer, you are the guilty culprit! (just kidding - can't blame the vendor here)

weird about the backfire in neutral, but expect an old hand @ Savages may have an idea for you.