I've got a Stihl FS46 trimmer. It's about 5 years old but was used very sparingly for three years before going into storage for the last two. It was always a little hard to start but was running like a champ when it went into storage. I've got it out of storage now, and it won't start. With everything I've tried, I've never heard a single combustion cycle. It doesn't even try.
It was properly drained of fuel before it went into storage. Since I've been trying to get it started I've replaced the spark plug, cleaned the brush contacts, and confirmed a good strong spark. No breakage in the fuel lines and they're still like new. After that I disassembled the carb and cleaned it, but when that produced no results, I bought a replacement carb. No change. Fuel is getting into the cylinder. So I checked the compression which is at ~110psi. I feel like that is a little low, but I'm not sure, so I disassembled the piston/cylinder to check out the rings. They weren't seized, no signs of excessive wear, and everything looked relatively good. Cylinder walls look like new and very little sign of blow-by on the piston. I cleaned everything up and after doing so it looks like new. Reassembled with the exhaust/muffler off to eliminate that as a source of problems. Rechecked the compression and no change, still 110psi. Still doesn't even try to start.
All of this was with the air filter off. This thing is about as simple a combustion engine as you can get so it's driving me nuts that I can't get it running. Fuel, air, spark. Simple. At this point I'd be happy just to have the fuel ignited in the cylinder once while I pull the starter string, even if it doesn't run.
Is 110psi low for this trimmer? Enough to prevent any ignition? If so does anybody have the part number for new piston rings? What else should I look at?
Thanks for the help.
#2
ILENGINE
Try putting a small amount of gas either into the intake or in the spark plug hole, and crank to see if it fires and runs until the gas gets burned out, keeps running, or no run at all. I would say 110 should be fine. Normally anything above 90 will work. I have worked on stuff that wouldn't fire below 175 but that is special occasions. The normal compression range depends on the compression ratio.
Are you using Stihl 2 cycle oil mix & high octane gas? Manual says 89 octane minimum, correct spark plug with gap of 0.02. Let us know how it works out.
Since you have a Stihl & not Echo I would suggest you purchase a small bottle of Stihl 2 cycle oil & pour it into empty 1 gallon gas can & fill it up with high octane gas, I would stay away from pre mixed gas & 2 cycle oil in a container for sale, quality does matter in this case since you have a Stihl and the pre mix you purchased at your hardware store off the shelf does have a shelf life, in other words if you mix it yourself at a reputable busy gas station you know you're getting quality vs. possibly stale gas at the hardware store.
Visible spark not always good spark. Poor man's check: Old spark plug gapped out to .100" +. Also my lowly Ryobi deveopled fly magnet/coil contact. Check for marks. Long shots but you're stuck, still?
You need a new spark plug!
Even though you have spark and spark may jump the gap when out of the engine, the plug can still be bad and won't fire under compression.
Unless you are getting too much gas causing a flooding situation.
#8
Fish
Remove the screw in exhaust tube out of the muffler with a 5/8-16mm wrench, and hold it up to a light, you should be able to see through it and the screen on the other side.
A trimmer that has been hanging in a garage for years usually gets wasp nests planting eggs in tiny holes all over small engines
Neither the muffler or exhaust are on the engine right now in order to eliminate them as a source of the problem.
This is the second spark plug that I've had in the thing with the same behavior. Not saying it's impossible, but it would be a long shot for both of them, one straight out of the package, to be identically bad. If it's a spark issue I'd put it on the ignition system. I have a digital multimeter if anybody knows the kind of numbers I should see from it, I can check.
I went out to work on the thing today and for the hell of it pulled the starter cord even though I hadn't done anything with it since the last time it wouldn't start for me. This time I got one combustion cycle (didn't prime anything) from whatever was leftover in the cylinder from last time, but I couldn't replicate it even by introducing fuel directly into the cylinder. I tried a different fuel source. No change.
