The 51's and 55's are excellent saws. We see a LOT of them with P/C issues, no doubt about it. I would imagine this happens simply because of the numbers of units sold and still in service after many years of less than adequate maintenence.
Also keep in mind that this new fuel requires more of it (less BTU's) and it's not a bad idea either to add some additional oil in the mix either. If you are a homeowner, or casual chainsaw user, it's unlikely the saws mixture screws will ever get touched, let alone take the limiter caps off of them. I have yet to find a 51 or 55 with the limiter caps in place, that would come within an ideal "range" with the "H" speed screw. They are too lean even with the screw maxxed out. This fact alone is going to toast some P/C's on high mileage units.
You've also got homeowners pulling them out after they have sat up for months or even years with old fuel in the tanks. Nothing harder on the P/C than some crusty fuel and a dull chain!
I've also been seeing a LOT of kinked, damaged and split fuel lines. As the fuel line sucks air instead of fuel, this can/will cause the saw to go lean when the leak is very slight, before it gets bad enough that the saw will no longer run correctly, another possible contributor to P/C failure.
This 51/55's were available for many years and came in several "flavors". I have one of each model here, an open port 51, closed port 55, and an open port 55 "Rancher". The closed port 55 is by far the fastest of the bunch, with strong top end power. It is not as "smooth" or broad of a torque curve as the 51 or 55 Rancher. I was cutting with it last night, and had thought I took the 55 Rancher to the woods. I was thinking to myself that the 55 was running better than it ever had, and was quite impressed with it. After finishing up the load, I went to strap it down on the Quad, and realized it was the closed port 55 I'd been using. I chuckled to myself for a second. I am very fond of that particular saw, it's like running a mini versioin of a 372XP.
As for P/C's, I ALWAYS use OEM, even if I get them from damaged used saws. Even though there were many minor changes to the 55's over the years of production, most parts will interchange between all models.
Another very good reason to use and rebuild these saws is parts support. With plenty of low hrs units out there with fuel system issues, or even P/C issues, you can get parts saws very reasonable. Far as I know, all the factory parts are still available as well?......Cliff
