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Professional Homeowner
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Discussion Starter #1
Title says it all. I’m starting to get a bit frustrated with this thing. Up to 120 PSI compression. Good spark. Replaced plug anyway. Gas directly into carb throat, carb cleaner in carb throat, carb cleaner in plug hole, dry off plug several times as necessary, compressed air blow out cylinder and out muffler. No matter what I do, it won’t even sound like it’s trying to start. It’s like there’s zero spark. Spark tester shows good with plug in tight and all hooked up. What am I missing???

Machine sat for a couple years with ethanol fuel in tank, hanging by the head end. Thanks, dad...
 

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maybe just remove it from the head, hook up a wire between the block and the plug ground, and in a dark room see if spark when you pull the starter. It's not definitive, as supposedly it's possible that under compression it may not spark the same way, but it would be a positive sign if it does spark.

Then maybe try a shot of starter spray in the intake and see if it tries starting. If it does, then that would point you back to the carb, if it doesn't, then (if it's a 4mix setup, I don't know if yours is) maybe check valve clearance.
 

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Discussion Starter #5
maybe just remove it from the head, hook up a wire between the block and the plug ground, and in a dark room see if spark when you pull the starter. It's not definitive, as supposedly it's possible that under compression it may not spark the same way, but it would be a positive sign if it does spark.

Then maybe try a shot of starter spray in the intake and see if it tries starting. If it does, then that would point you back to the carb, if it doesn't, then (if it's a 4mix setup, I don't know if yours is) maybe check valve clearance.
Yessir, very strong blue spark. Tester indicates there is still spark with plug installed, not sure if that means there’s spark at plug when in engine. I don’t know if it’s a 4mix or not. I’ll have to do some research on that one. The recoil is interesting though. It doesn’t matter how hard I pull it- it always spins pretty good when the rope is about halfway out... like it’s an easy start system or something. I can pull it harder and it spins faster, getting me the 120 PSI on the gauge.
What are the odds that the NGK could be bad right out of the box and display the same symptom as the factory plug? Maybe also I should get some actual starting fluid rather than the carb cleaner I have now.
 

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Have you tried cleaning the carb? If the carb is feeding too much fuel, spraying other flammables into the carb won't lean out the mixture. Does the plug look wet when you pull it?
 

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Discussion Starter #7
Have you tried cleaning the carb? If the carb is feeding too much fuel, spraying other flammables into the carb won't lean out the mixture. Does the plug look wet when you pull it?
Yes, plug looks wet when pulled. I didn’t try cleaning the carb yet, but I did dump the fuel into my general 2 cycle can and drain the primer system before attempting any of this. Fuel didn’t smell too awful, so I figured a couple ounces in 3/4 gallon of fresh wouldn’t be noticed by my other equipment (so far I’ve been right... chainsaw and pole saw still running good on it). I took out the original plug and cleaned it before squirting in some carb cleaner and ripping the cord a couple times, eventually pouring a few drops of gas into the carb. At that point I hadn’t refilled the fuel tank yet.
 

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It is probably similar to the 27.2cc 2-stroke that is on my FS-38 which has served me well for years. I store it hanging by the head with the gas cap left loose so that the duckbill vent doesn't create pressure in the tank forcing the fuel through the carb.

I read that the spark arrestors tend to clog up and so you should check it.
 

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I'd say take your carb apart, check your needle valve, and clean everything. Amazing how much even the slightest gunk in a carb can do
 

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Discussion Starter #11
It is probably similar to the 27.2cc 2-stroke that is on my FS-38 which has served me well for years. I store it hanging by the head with the gas cap left loose so that the duckbill vent doesn't create pressure in the tank forcing the fuel through the carb.

I read that the spark arrestors tend to clog up and so you should check it.
Ok, I blew air through the spark plug hole and saw a bunch of vapor blow out of the muffler. I thought that meant it was clear, but perhaps I need to look into it further.
 

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Discussion Starter #12
Reporting back:
Today I removed the muffler, checked the spark arrestor (it was clean), and stuck a butane torch in it for a few minutes. Smoke rolled out. Tried restarting it without the muffler, and it fired right up. Reinstalled muffler - no go. Removed muffler and placed on propane grill on high for 2 Seagrams Coolers. Reinstalled muffler, restarted and ran perfectly. Muffler must have been plugged.
Problem solved.
 

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Congrats at finding the problem. How old is this unit? I guess it really depends on the hours of use but they don't have run hour meters. Also probably factors on how long you run it for as to how hot the muffler gets. What ratio mix and brand do you use?
 

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Discussion Starter #14
Congrats at finding the problem. How old is this unit? I guess it really depends on the hours of use but they don't have run hour meters. Also probably factors on how long you run it for as to how hot the muffler gets. What ratio mix and brand do you use?
I use I think like 2.3 or 2.6 oz oil to a gallon of gas. I use synthetic 2 stroke oil in the squeeze bottle with the graduated lines in the tank at the top of the bottle. Brand varies. Ethanol fuel is generally used, I believe standard grade 87 octane. I've really never noticed a huge difference in the way my 2 cycle stuff runs. I used to run non-ethanol, but I really didn't see the benefit any more so I stopped.

This trimmer is my dad's. He runs the Stihl oil in the pre-measured bottles mixed into a gallon of gas. He bought it at a garage sale for not very much money ($50?) about 5 years back. He uses it VERY little. I have no clue about how it was used before he got it, but judging by the condition of it, I'm going to say it was never used much. This is the first time I've ever played with it.
 

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I have a FS44 that didn't run well on pump gas mixed, I picked up some Stihl Motomix years ago and it runs great. I only put Motomix or Trufuel in my 2 strokes. Tossed several Lawn Boys due to ethanol fuel.

CCMoe
 

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STIHL recommends a mix of 50:1 high-quality 89 octane unleaded gasoline to STIHL engine oil. Oil is packaged in 100 ml, 200 ml, 500 ml and 1 litre bottles in Canada. In the US, the smallest is 2.6 oz. I have to assume you used that size to a gallon of gas.

 

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Discussion Starter #18
Got to tearing into this thing today. Quick disassembly of the carb revealed the fuel intake screen full of what sure did look like sawdust. Tank is clean, though. I wonder what it was.
Sure did suck when I blasted the screen out with a short mild burst of air and it went away. Had to scour the shop floor with eagle eyes to find it. Also squirting carb cleaner into the primer circuit blew apart the check valve assembly inside the bulb. Well, at least all those parts stayed inside the bulb. Just had to figure out which order they went back in.

Starts and runs good, for now at least.
 
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