I would like to encourage you to get a set of new burrs.
Burnt taste is the usual warning sign of dull burrs that need replacement. Often, you can't see it on the burrs, but you can feel it. They should feel sharp to the touch, being able to scrape your nails for instance. Much like a newly sharpened knife.

It can be somewhat of a surprise, the first time you feel how sharp burr sets coming fresh from the factory really are. If you have never tried it, you might easily fool yourself into thinking the burrs are OK when they are not.

Edit- Addendum, becoming longer than the original text... sorry: All too often, we get hold of used pro grinders that according to the previous owner have seen "little use", "low-volume use", "sitting-in-the-corner-used-only-for-decaf" or something to that effect, when in reality, during their service, they have actually seen quite a lot of use, although maybe not at all as much as the owner's main grinder. Some of them also get to see a fair bit of abuse. This does not go unnoticed, even if the grinder looks OK on the outside.

As an example from my own experience, I have a Max at home right now which is in dear need of new burrs and a very thorough cleaning - it smells like... bleeaahhh! Like someone used it as an ashtray. The burrs are so dull it can't even grind for espresso. I am even thinking of changing the auger (conical) burrs... which might be unheard of for a Max, but looking and feeling the auger burrs, I do consider it. The axis is slightly wobbly - if this is normal or not, I don't know, but this might be a result of plain bad user habit: changing grind setting when the grinder is standing still is NOT recommended according to the manufacturer, as it may damage the grinding mechanism. Straightening that axis (if needed) might prove impossible.

According to the salesman, this Max had been "used for about a year", low-volume use. I hope and believe it can be fixed, but to be honest it looks more as if it had been in high-volume use for five years or so, and abused at that. Good deal? Well, you get what you get when it comes to pro grinders. The market is very small, so if you got a good price and you only need to change burr set, you can consider yourself lucky.

Thanks all for the many suggestions and observations.
The new burrs are scheduled to arrive tomorrow. I took the old burrs out. One of the screws holding in the top burr was nearly stripped, so they must have been changed at least once before. I had to use WD-40 to get the screws loose in both the top & bottom burrs and am a little worried that the residual odor may be imparted to the coffee. I was considering putting some baking soda in the dozer to absorb the odors, thinking that the sweep in the dozer will push the soda out to remover it. Once the burrs were removed I completely cleaned & vaced the grinder and dozer. There were old oily grinds were caked on the base that holds the bottom burr. I sure that was the source of some of the stale coffee smell that the grinder retained even after the first time I cleaned it. I'll try the 91% isopropanol or JoeGlow if I can find it. I bought the Rossi RR45 for $120 plus about $50 with shipping for the burrs. The Rossi is suppose to compare favorably with the Rocky & Mazzer Mini, both machines I looked for used but couldn't find. If I get good results for $170 out of pocket, it will be worth it.
Michael