Stihldoc
Analog old guy in a digital world
Today was one of those great days where things just fell into place. I had a full list of shop jobs that needed to get done and everything went great UNTIL I got to an MS660 that "wouldn't start". This saw belongs to one of the landscapers we regularly do service work for, but rarely see for repairs. I'll call him "JP". JP's equipment is very well treated as landscaper stuff goes, he has good employees who generally treat equipment with respect. Its unusual to have any of his stuff come in for more than routine service. Not today. His MS660 with a 36" bar came to me with the usual "won't start" complaint on the service order. Our countermen are a mixed bag- sometimes I get good info on a ticket where they've taken the time to talk with a customer about how something is running, and sometimes not. This was one of those "not" instances.
My general impression of the saw (I'm an EMT too, so we're big on general impressions) was that it was well-treated, well maintained, and the chain was razor sharp. Thats unusual in and of itself. The tank contained what looked and smelled like good mix and all the basics were OK.
A quick pull on the rope told me that the compression felt low. Check deco valve, it was closed. Crap. Not good.
I drained the fuel into a glass jar and waited to see what it looked like- it was good clean mix. Greenish-blue in color, probably using Stihl mix oil. Check.
I removed the muffler and confirmed what my right arm told me- the cylinder and piston were severely scored and there wasn't adequate compression to start. At this point I did a pressure and vacuum test of the crankcase to see if an air leak was present- no air leakage. As I went through my checkout, I became more and more puzzled because everything continued to check out properly. Fuel filter, fuel hose, etc... no reason found to account for the failure.
That is, until I got to the carburetor, Its a Walbro WJ-69. This is generally a bulletproof carb and I have no issues with it whatsoever. I pulled the metering cover and checked the lever height- OK. The pump cover was next- no sawdust in the inlet screen. So far so good. As I looked closer at the carb, the inlet screen just didn't look right- it wasn't the right color. I removed it and let it dry on the bench for a few minutes. I went at it with my Sherlock Holmes magnifying glass and saw that the mesh was completely filled with deposits.
AH HA!!! Finally some evidence.
I spoke to JP about the failure and he said he hadn't run the saw for 6-8 months prior to its most recent and final use. He said he had left fuel in it, which "smelled bad" and he dumped it out prior to adding fresh mix and using the saw. But, the damage was done- the inlet screen was clogged and the saw ran lean despite the new fuel.
Systematic troubleshooting and good communication with JP solved this mystery. I learned a lesson today, as did JP. We're repairing his saw and he's switching over to MotoMix for storage.
My general impression of the saw (I'm an EMT too, so we're big on general impressions) was that it was well-treated, well maintained, and the chain was razor sharp. Thats unusual in and of itself. The tank contained what looked and smelled like good mix and all the basics were OK.
A quick pull on the rope told me that the compression felt low. Check deco valve, it was closed. Crap. Not good.
I drained the fuel into a glass jar and waited to see what it looked like- it was good clean mix. Greenish-blue in color, probably using Stihl mix oil. Check.
I removed the muffler and confirmed what my right arm told me- the cylinder and piston were severely scored and there wasn't adequate compression to start. At this point I did a pressure and vacuum test of the crankcase to see if an air leak was present- no air leakage. As I went through my checkout, I became more and more puzzled because everything continued to check out properly. Fuel filter, fuel hose, etc... no reason found to account for the failure.
That is, until I got to the carburetor, Its a Walbro WJ-69. This is generally a bulletproof carb and I have no issues with it whatsoever. I pulled the metering cover and checked the lever height- OK. The pump cover was next- no sawdust in the inlet screen. So far so good. As I looked closer at the carb, the inlet screen just didn't look right- it wasn't the right color. I removed it and let it dry on the bench for a few minutes. I went at it with my Sherlock Holmes magnifying glass and saw that the mesh was completely filled with deposits.
AH HA!!! Finally some evidence.
I spoke to JP about the failure and he said he hadn't run the saw for 6-8 months prior to its most recent and final use. He said he had left fuel in it, which "smelled bad" and he dumped it out prior to adding fresh mix and using the saw. But, the damage was done- the inlet screen was clogged and the saw ran lean despite the new fuel.
Systematic troubleshooting and good communication with JP solved this mystery. I learned a lesson today, as did JP. We're repairing his saw and he's switching over to MotoMix for storage.
