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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.

Check to see if the spark arrester is clogged.

mechanic mark said:

Kawasaki BPR4ES SPARK PLUG BPR4ES

www.kawasakienginestore.com

Click to expand...

I put in what came out NGK BPMR7a. That one looks a lot different. But, reading the operator manual it specs a Bosch USR 7 AC which is quite different from what I took out also. Snout looks a lot longer.

My saws take the BRMR7a so maybe I screwed up at some point?

Rivets said:

Check to see if the spark arrester is clogged.

Click to expand...

I'll check that too, when I get the correct spark plug.

Check the valve clearance.

mechanic mark said:

Kawasaki BPR4ES SPARK PLUG BPR4ES

www.kawasakienginestore.com

Kawasaki Engine Tune Up Kit Locator Guide

Click to expand...

? It's a Stihl Trimmer FS90R 4 Mix

hlw49 said:

Check the valve clearance.

Click to expand...

Don't see any procedure in the users manual. It's a "take to dealer" thing. I'll look for how to do it.

joea99 said:

Don't see any procedure in the users manual. It's a "take to dealer" thing. I'll look for how to do it.

Click to expand...

I think I saw a how to on You ... know where.

tgzzzz said:

I think I saw a how to on You ... know where.

Click to expand...

Paid a visit to the "Saloon". Looks pretty simple.

A 7 is a lot lot colder than a 4
So what is happening is the spark pug is not getting hot enough to prevent carbon build up
And the carbon build up provides a conductive path down the side of the insulator so the spark tracks don the nose rather than jumping the gap .
This is of course assuming that the 4 is in fact the correct plug heat ( check your owners manual ) .
Bosh heat grades & NGK grades are pretty well similar and run hot in the low numbers & colder in the higher numbers and a 7 is quite a cold plug .

joea99 said:

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.

Click to expand...

See page 47 in manual above.

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.

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.

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

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.

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.