Perhaps the infamous noisy speedometer cable. Mine lets out a squeal and rattle now and then under acceleration. Check your speedo cable and lube as necessary, just to see if that's it. Never hurts to give it a look anyway, even if it's not the problem.

Regards,
Banger
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Are you sure the sound originates from the gearbox?  Your word discription of the sound makes me think of "pinging", or detonation, which would be expected from a hot running engine (stock Savage engine running very lean) that is under load (accelerating) and running on regular fuel (I think premium is best for an air cooled engine).

**I just looked back at your write-up and noticed that your weather is very cold...that makes for more dense air which makes for a LEANER running engine...which increases the chance of detonation.

Yes, I would rejet and tune the carb...at least the pilot jet...but as long as the float bowl is off you might as well go up on the main jet as well...and shave the spacer or add tiny washers to the jet needle if you are you are up to it.

pilot jet.......low range
jet needle...midrange
main jet.......high range


The Savage is SO LEAN as it comes from the factory that it is almost crazy.  To richen the carb so that it is running with a MORE IDEAL fuel/air mixture is just good for the engine, and it will respond better and make more power.

If you will be getting those pretty soon that will be a good way to go and save an extra tuning day.  However, if it will be a while before you do the muffler/K&N switch then I would at least put in the larger pilot jet.  That is quick and easy and will stop the backfiring...which is not very good for the engine.

im about to buy my new pilot jet and have seen pictures of people with pilot jets with bleed holes. should i get the one with the bleed holes or without?

here is the link.

http://www.carbparts.com/mikuni/mikuni_tuning.htm

i beleive in one of greg650's tech sections i saw his pilot jet with bleed holes.  mine doesnt have and bleed holes.

i just placed an order for a bleed one.  we will see how it works out.

I used both on the stock carb when it was still on my engine and could not tell much of a difference.  According to the tech stuff I have read the one with the extra holes does the transition from idle to 1/4 throttle a little smoother than the single hole version.  Apparently the difference is so small that you do not really feel it, but it can be charted on a dyno/computer which monitors the fue/air ratio down to the last droplet of fuel.