I did test it when I first put it together. I have put a bunch of hours on it sense I put it together and it has always been a great saw. It feels like it still has good compression and all. I do think I developed a air leak and think I may have blew a crank seal. I used Three Bond gasket sealer on the case halves when I put it together along with the gasket. I pulled the carb and ran my finger down the intake tube and it felt like everything was alright but you never know. I just need to break it down and see what is wrong. I did order new crank seals and another carb and a few other parts like a gasket set and so forth just to keep on hand. Like I said I have cut a lot of wood with it to this point, a lot of big wood and it had performed great until this point. I am going to wait until the big bore kit and seals come in and tare into it and see what is going on. I love the saw and it performs great. A friend on the McCulloch site and I are making a chainsaw dyno. He has 2 factory Stihl MS660s. I am wanting to put both on the dyno when we get it finished and see how my saw performs against a factory Stihl. I am also going to order a 070 kit. Don't really need a saw that big as I have a McCulloch SP125c but I just like the look and sound of the 070 you put on Youtube. They just look and sound soo cool. When I find out what went wrong I will post it here. I am sure it is not much as it has plenty compression and will start if primed. I have been getting some really bad gas lately and just wonder if maybe the carb is stopped up and I did not see it because I cleaned the carb out in the field and used a can of starter fluid to blow threw the jets. It was all I had, a guy had it in the tool box on his truck.
I own a motorcycle shop and this is a pic of a set of carbs that I cleaned in the heated ultrasonic. The guy could not pick it up for a couple weeks. When he came to pick it up it would not run properly and fuel started pouring out of the over flows so I pulled the carbs and this is what I found. This from setting 2 weeks and the fuel that was in his tank came from a station that advertises no ethanol.
Here is the carbs after I had ran them threw the cleaner for the second time. You can see a little corrosion left in them but a lot cleaner than before. I drained the gas from his tank and put in fresh. I took some of the old fuel and put it into an old genset I had just repaired the gas tank with redkote and JB Weld. (an old genset I have had for many years and just keep around for what ever) I started smelling fuel and found it pouring out of the tank. It had ate threw the redkote and the JB weld felt like clay. I have never seen this before and I have repaired many tanks throughout the years like this.
So it could very well be the fuel/carb. By the way the fuel the spilled out onto the floor of my shop ate the 10 year old paint that nothing else had ate threw it bubbled it up. Don't know what is going on with the fuel but always suspect it from now on.
Brian