+1 on double checking the brackets. I went down that road some time ago, repaired the original breaks with bolted-on reinforcements, eventually the brackets broke in a different location. I finally replaced them with the new updated brackets.
Another thing to look at is the tune in the 1000 - 1800 rpm range. Mine was extremely lean, making the engine run very rough in that range. After richening the mixture it smoothed out to the point I could putt around in the neighborhood at 1500 rpm without all the shaking and drama. Before whenever riding and slowing before a stop, as soon as the rpm's dropped below 2000 the bike would stumble and buck. Now it runs smoothly.
Jerry