here is the problem with 661's or any mtronic/autotune
1. not running correctly
2. taking 3,4,5, 10 pulls to restart after shutting them off
3. not restarting after refueling unless leaving them sit to cool off
4. in allot of cases multiple new solenoids/modules per year to keep them running.....last one i worked on the poor guy had installed 3 solenoids in something like 8 months...thats roughly $100 per crack for diagnostic/parts. considering the old 660 would run a year without touching it and these require multiple trips per year to even keep them usable for a guy that puts a gallon+ of fuel per day thru them....that alone is enough to not like using one commercially. And before the excuses come that it is the fuel or oil he is running....his 6400 has been in service for the same time period using the same fuel without so much as a hiccup and the 660 even longer.
5. only a stihl dealer can work on them(electrically) and in our case locally its over an hour drive minimum to get to a dealer that has a clue on Mtronic
we could go into the pistons and P&C kits....I've sold more 661 pistons than 066/660 pistons....maybe thats just a coincidence though but the piss poor filtration of the 661 isnt just a fluke, thats a fairly well documented issue.
If i would have had 4 of the euro setups on hand today I could have sold 4 to a logger to get rid of the mtronic on all 4 of his saws but i only had 2 so he bought 2 and is waiting on me to get 2 more so he is rid of mtronic completely.