My stihl FS-110 weed whacker had been acting up. Bogging down, wouldn't rev back up. took it into the dealer, he said it was all gummed up from the oil I'm running (amsoil dominator). I seem to recall prior discussions that the 4-mix engines run best on (and perhaps need) Stihl Ultra. Anyone offer thoughts?
Stihl 4-mix engine oil
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SteveSr
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4-mixes will do this. I had one that was used by one of our trail crews do this. Engine was basically new but full of carbon. Had to completely tear it down and clean it up.
Suspected cause but never confirmed was excessive oil and/or overloaded powerhead by using .140" (diagonal) square line.
You should be using an FD rated oil which Ultra is NOT (only FB). FB oils have no detergent package to clean/remove carbon. THe newer FD formulations do. Is Dominator rated for air-cooled engines? What is its JASO F? rating?
Suspected cause but never confirmed was excessive oil and/or overloaded powerhead by using .140" (diagonal) square line.
You should be using an FD rated oil which Ultra is NOT (only FB). FB oils have no detergent package to clean/remove carbon. THe newer FD formulations do. Is Dominator rated for air-cooled engines? What is its JASO F? rating?
I run 32:1 Echo Red Armor in my KM91 just as I do in the 2 cycles. I have only had the 4mix for this summer but so far it has done well. This oil is known for being very clean running. I have no oily exhaust even though it is @ 32:1.
I’d check the machine over myself to confirm. Dealer is likely giving his normal reply to the average customer running Ultra.
Not saying Dominator didn’t clog it up, it’s just more likely to me that the dealer said what he always says
Not saying Dominator didn’t clog it up, it’s just more likely to me that the dealer said what he always says
Well, I absolutely despise Amsoil but dominator is not what you wanna be running in small two cycle equipment. Saber is a cleaner burning oil where as dominator is not. “Racing use only” as the ass clown independent salesmen say.
Most people that have never used it say that. It says “racing use only” because it doesn’t have a fuel stabilizer in it.
Ultra was designed around the 4mix engine.
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Dominator in reality is cleaner than Saber.
The advice you have given is perfect for an air cooled two cycle, but poor for a 4mix.
The 4mix is a terrible design and really runs longer before valve adjustments/issues with an ashless oil. Which is why Stihl had Ultra formulated they way it is.
I'd be inclined to stick with Ultra to be honest.
I run saber in all my machines like that never had any gum up. Usually the carbs go bad though. OP what ratio of oil and are you running it at low RPM a lot?
Running (or was running) 45:1with non-E gas. And yes, a lot of low RPM as using it on a gravel driveway when the issue started.
I still have some Ultra and plan to try running it for a while and see how the machine does.
I'll stick with the Dominator in everything else Saws and blowers).
Well that's why it gummed up. Maybe you could do the stone area first then run the hell out of it on the lawn or something.
Say what you want, it has been documented by Stihl that Ultra was formulated for the 4mix engine.
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I've tried running the hell out of it to clear it up, hasn't worked out very well.
It worked for me for years without this issue mostly running Mobil One 2T. Only really became an issue with the Dominator so I reckon I'll try the Ultra for a while and see how it goes.
Any comment at to whether it is better suited for a pole pruner vs a string trimmer. It is pretty obvious they make a lot of them.
Mine in the pole saw configuration works great, sounds powerful. Must be 10 years by now. I use sabre 45/1 approx.
Honda and Makita and likely others have all position 4 cycle similar devices, not mix oil. The exhaust isn't as bad but do not have the sound at least for sawing under load.
Outboard / ashless works the best in the 4 mix engines. JASO FD oil contains low ash additives that will cause nasty deposits around the valve stem, ports and seat.
SteveSr
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Pull the muffler and look at the exhaust port for accumulated carbon. While you are at it you can pull the spark screen off the muffler and burn it clean with a torch.
The gold standard is the conventional 4-stroke leakdown test to see how much the valves are leaking.
What are the ratings? JASO F?
At this point you likely have an engine full of carbon which Ultra won't (actually can't) clean up. Your best bet is to use an FD rated oil and clean as much carbon out of the exhaust port and muffler as possible.
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