Had the same problem on our 08 8010 and have heard of 8120&9120's with the same problem. The isue is the aspirator we had the shop come out and vacuum test ours, supposed to have 25 inches of vacuum minimum!! Ours has 5 so case is now apparently aware of the problem and working on a new muffler with a better aspirator. I went to the local muffler shop and had them make me aspirator that bolts on the top of the muffler and connected the hose to it, meanwhile I blocked the hole in the muffler where it previously hooked up to. It now resembles the old style ones on the 2388 and such, haven't tried it cause we are done but hopefully they will come up with something before next harvest!!! Another example of poor R&D!!
P.S.
Our 8010 was down on power earlier in harvest and we took apart the venturi and the holes were half plugged with chaff. All seals were inspected and silicone used EVERYWHERE!