I just recently bought a Breville 870 and started off with starbucks beans. Worked ok and the grinds seemed to come out as fine as I would like them. Today I stopped in and bought some locally roasted beans (which taste way better) and haven't been able to get them to grind properly. I emptied out the bean hopper and partially took apart the grinder to get the residual starbucks out of it. When I replaced the grinder and hopper to grind the new beans, the grounds came out much quicker and in larger quantities than with the starbucks ones. I also couldn't get them to grind near as fine. Is it something to do with the grinder? The beans? Do I need to mod the machine like I have seen done to other Breville 870s?

Even though it was under extracted, the flavor was waaaaay better. The starbucks stuff always came out bitter, even when under extracted.

EDIT - I fixed the problem. Turned out I wasn't getting the top burr all the way back in. I removed it and cleaned the grinder out. When I replaced it, the top burr was seated correctly and all the way in. Now they're coming out too fine, ha. A couple adjustments and I was able to pull a decent shot.

You probably did this, but double check you put it back together ok, the upper burr may not be seated all the way, e.g. grinds in the way. You won't have to grind Starbucks as fine because it's darker, but you should be able to grind light beans fine enough for espresso, at least I can no problem. You might try increasing your dose, that may help if you are significantly underdosing. I haven't looked inside, but it obviously has a stop which most likely can be removed to allow finer grinding, but I would recommend exchanging it first if you can't resolve it, you may have a dud.

Yep, exactly that. It was the top burr. I definitely am not underdosing, I am probably overdosing in fact. As for the starbucks beans, I definitely see the difference now. They are worlds apart. Now I see why so many people say that starbucks burns their beans.

Yeah, what's funny is you can put their medium and french roast side by side and you can hardly tell the difference.

I see you're not in the area but if you're curious, I ended up with "Get Roasted... Locally" beans. I got the Deep Blue blend. Might try out some more of their stuff on my next purchase. http://www.roastedlocally.com