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Playin' In The Dirt Again
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Discussion Starter · #1 ·
Hi Forum.

I have a Stihl FS 1200 weed eater with the nylon cutting blade head.

Today I cut a lot of tall brush around my property, about 2000 square feet. I noticed something that was unusual, and that followed by difficulty in restarting, and then no restarting at all.

After just about depleting the first tank of fuel, I notice intermittent loss of power under load. I supposed it to be very low fuel, since the tank was nearing empty. I filled the tank and started it up. But it took a number of pulls to get it going. It really didn't want to go. In the past it would have restarted while hot with no difficulty.

Then I cut a lot more brush, using about half a tank of fuel. As I was approaching the end of the work, I realized I needed new nylon cutting blades. Just before I stopped the motor, I noticed that intermittent loss of power again, a sort of slowing of the engine for a few seconds, followed by a return to full power. I stopped the motor and swapped the blades.

Then it would not crank at all. I pulled maybe twenty times or more. Then I decided to check for fire. I took the plug wire and attached it to a new plug. Leaving it outside the motor, I connected its body to chassis ground. Then I pulled the string. I saw no spark. I did it a number of times, not trusting my vision. There was no spark.

I noticed that on previous occasions it was hard to restart after running, but had been easier to start the next day. I am hoping that this will be the case tomorrow.

What would you do to address the problem? Is it the coil? The solid state ignition circuit? A capacitor? Could it be fuel, air, or adjustment?

What do you think? I'm trying to avoid a trip to the repair folks. Last visit a year ago they replaced the ignition stuff and charged me $85. Now I seem to be having similar problems again.

I wish my Stihl weed eater was an Echo. I have never had motor problems with Echo products.

:Tractor2:
 

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Never heard of an FS1200. Is it current or an older model? In any case, when checking for spark, the plug will have to be grounded to a metal part of the machine. Some electronic ignition sparks are very faint, and are best seen in a dark room.
 

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No spark could be a lot of things, but first I would get a new spark plug or swap it with a known good one.

There's a pretty good chance your trimmer doesn't have points, so assuming the plug is good I would check the following.

1. Remove the shroud of the engine, check the plug wire for any fraying where it could ground out. Also remove the handle and check the kill wire (comes out of coil, grounds to engine to shut off spark). Make sure it's not been rubbing the flywheel or has melted through.
2. If the wires are fine, reset the coil gap. I just slide a business card in there.
3. If you still don't have any fire, I would probably look into the coil.
 

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Playin' In The Dirt Again
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194 Posts
Discussion Starter · #4 · (Edited)
Never heard of an FS1200. Is it current or an older model? In any case, when checking for spark, the plug will have to be grounded to a metal part of the machine. Some electronic ignition sparks are very faint, and are best seen in a dark room.
Uh Oh. It's an FS120, not an FS1200. I bought it new in 1998. Thanks for the tip about checking the spark in darkness. I was outdoors, and a spark would have been harder to see there.

I was using a clip lead test wire to ground the washer of the spark plug to the body of the motor, by way of a bolt that goes into it.

:Tractor2:
 

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Playin' In The Dirt Again
Joined
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194 Posts
Discussion Starter · #5 ·
No spark could be a lot of things, but first I would get a new spark plug or swap it with a known good one.

There's a pretty good chance your trimmer doesn't have points, so assuming the plug is good I would check the following.

1. Remove the shroud of the engine, check the plug wire for any fraying where it could ground out. Also remove the handle and check the kill wire (comes out of coil, grounds to engine to shut off spark). Make sure it's not been rubbing the flywheel or has melted through.
2. If the wires are fine, reset the coil gap. I just slide a business card in there.
3. If you still don't have any fire, I would probably look into the coil.
Thanks for that handy checklist. I will do those things. Great tip about the business card.

I noticed that when cold the weed eater cranked okay yesterday. After about twenty minutes of heavy use in cutting brush it did that power loss thing again... a drop in power as if fuel was being starved and then a return to normal power for a minute or so... and then loss of power again in the same way.

I will post the solution here when I solve it. :thanku:

:Tractor2:
 

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another common problem with the 2 stroke motors especially with a few years on them is the main seals on them wear out and leak air into the cylinder and then add air to the air fuel mixture causing them to run erratic or loose power while running it at different speeds rotate the motor 90 degrees side to side even watch for a change in rpm while you are holding the throttle steady if you notice a surge in rpm you probably have a seal leaking its not a big job to fix but if not repaired besides being hard starting and running erratic it can cause your engine to run lean and lead to scoring in the cylinder. I was a Stihl certified wrench for 10 years I've seen a lot of bad seals in that time
 
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