FS90R running rough, stalling

[mechanic mark]

Worked good last week. Put in new fuel today, fired up quick, but was "missing", puffing a wisp of white smoke. Warmed up a bit and stopped smoking, but would not reach a "smooth" top speed, appeared to be struggling and never reached "normal" top speed. Struggled to cut any grass.

Pulled the plug which appeared "wet and sooty". Put in a new plug, gapped at .020 and it ran better for a few minutes then started stalling out. Restarted a few times and still would not "max out" for speed and struggled to cut.

Pulled the plug and it appeared to have sooted up already, not even 5 minutes of running. But only on one side of the plug. Pictures attached.

https://cdnassets.stihlusa.com/1625863477-stihl-fs-90-owners-instruction-manual.pdf

See page 47 in manual above.

 

[Fish]

Just a quick test. Take off the air filter and start it. See if it improves the performance.
It may just need a good bath.

 

[Fish]

Just a quick test. Take off the air filter and start it. See if it improves the performance.
It may just need a good bath.

 

[hlw49]

Did you adjust the valves. They set .004 on both valves,

 

[joea99]

OK, so, I screwed up and wasted a lot of peoples time. I do have an FS90R. It has been stilling cold and forlorn in the back of the shed while I enjoyed the services, reluctant as they were, of the FS80R I was actually using.

Sigh. Age and ignorance are a terrible combination. So, cleaned the new oily plug with some cleaner, pulled the spark arrestor and hosed it off, though it was not bad, I could see thought it. buttoned it up, static set the carb screws and fired right up. Still smoking a bit at idle, but once warmed up it ran fine. Just a slight tweak on the H screw to speed it up a bit.

After some sulking I got out the FS90R, bemoaned dirt and grim, fully expecting it not to run at all, since "someone" left fuel in it last year. Dumped it out, environmentally conscious of course, dribbled in some fresh and pumped the bulb "a lot". Fired on first pull. Well, popped on first pull anyway. Runs fine. So nice I wonder why I was not using it all along.

I had a video of the FS80R running but I cannot upload it, too big.

 

[jviews12]

Maybe a bad load of gas? Since it ran fine in the past with the "old" plug, what changed was gas. If true, drain lines, carb, tank and get a new load of gas.