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I gave up on 2-stroke trimmers and got a rechargeable electric.
 

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I still would like to know what caused this compression failure?
Probably lean running. I always jet my two-strokes a bit rich, from what I understand, the plug should be darker than it would be on a 4-stroke. Two strokes "gain" a lot of power when they run lean, i.e. the engine runs faster, but with less and less power as the mixture leans out. This adjustment is much more critical than on a four stroke since your oil supply is tied to your gas supply.

You could try honing the jug to knock any glaze off and put new ring(s) in it, two strokes can be surprisingly resilient. I've heard of many moped engines which have seized and been recovered.
 
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Probably lean running. I always jet my two-strokes a bit rich, from what I understand, the plug should be darker than it would be on a 4-stroke. Two strokes "gain" a lot of power when they run lean, i.e. the engine runs faster, but with less and less power as the mixture leans out. This adjustment is much more critical than on a four stroke since your oil supply is tied to your gas supply.

You could try honing the jug to knock any glaze off and put new ring(s) in it, two strokes can be surprisingly resilient. I've heard of many moped engines which have seized and been recovered.
- Always adjust the carb so its slightly missing at full throttle/ no load. ( fourstroking ) as he wrote, a lean running two stroke will sieze but itll run very good until it does.
- you cant combat this with higher oilmixes...well, you can in a way if you go so far that it doesent run well.
- they usually siezes at the exhaust side.
- its not the lack of oil that makes it sieze, its the elevated temperature at the exhaust port thats damaging the piston. ( just like exhaust valves on a four stroke, but way more sensitive.)
 

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Discussion Starter #45
. . . .Probably lean running. I always jet my two-strokes a bit rich, from what I understand, the plug should be darker than it would be on a 4-stroke. Two strokes "gain" a lot of power when they run lean, i.e. the engine runs faster, but with less and less power as the mixture leans out. This adjustment is much more critical than on a four stroke since your oil supply is tied to your gas supply. . . . ..
So a lean air fuel mixture causes an engine to run hotter??? That seems strange as more ambient air would tend to have a cooling effect on the combustion chamber which would mean the engine runs cooler???
 

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With the 2 stroke it's the fuel and 2 stroke oil mix that cools the combustion process. I have a bunch of 2 stroke machines:
1998 Toro 3000 GTS 2 stroke snow blower
2005 Echo Leaf Blower
2005 Echo string trimmer
2008 Echo hedge trimmer

Of the 4 of them I've cleaned out the carb on the Toro 2x over the years and replaced it 2 seasons ago because it developed thrittle shaft wear which caused uncontrolled revving. After that much better (Suzuki 47p 2 stroke basiclly bulletproof)
On the Echos I had to clean out the carb on the leaf blower once and replace the ig coil once. That's it the others have needed nothing. I use the best Syn 2 stroke oil I can find and marine stabil. All we have here in Southern NY is e10. They all start well, the Toro usually on the 1st or 2nd pull, the others on the third or fourth. These machines get used a lot because we do most of our own landscaping and snow removal.
I also have a 30 year old MTD push mower with a 3.5 Briggs, and Briggs powered lawn vacuum, pressure washer and emergency generator (125 hrs during Sandy)...
2 stroke carbs like the one shown can be taken apart sprayed with carb cleaner and then blow out the passages. Many you tube vids on this....(see '65 Fords Channel or DonnyBoy both excellent)....
 

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Lean operation always causes hotter temperatures. Fuel burns faster and hotter in the presence of more oxygen. It's raw fuel that cools the combustion chambers.
 
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Right, most of your cooling comes from the incoming fuel mixture. The lean burn is also a fair bit hotter than a rich burn. Combine these factors together and you get a charge generating more heat and with the engine getting less oil per piston stroke than it should be (even if your fuel:eek:il ratio is spot on, if the fuel/oil: air ratio is off, you're losing quite a bit of oil for any given operating condition).

The other thing that I would note is (and I think others have mentioned this) two-stroke gas does separate over time. The lighter molecules (i.e. fuel) will naturally separate from the heavier ones (oil) over time. This could result in some of oil, along with some components of the gas, consolidating into an insoluble blob at the bottom of the gas can, given a long time. Even if the fuel is chemically stabilized, it's not necessarily mechanically stabilized. This means the first pour you get off of a can of old two-stroke gas could be mostly fuel, and 50:1 factory spec doesn't give you a whole lot of room to play with on the ratio. I try not to use any two-stroke gas that's older than a month or two, and if I do have to use an "old" can, I give it a good shake to blend everything back together as best I can.
 

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Another thing I'll add, I usually will give the old carb one shot at a cleaning and rebuild. If it still runs bad then I replace the carb with new. Just did this with the Echo ES 230 shred/vac. Got a new OE carb and it runs better than it did when new. We have it about 15 years. I am considering changing to Trufuel engineered fuel, with no ethanol and fuel stabilizer mixed in. They have both a 2 stroke with 50:1 oil mixed in and a straight gas version. But its about $20 a gallon! Might be fine for someone who only runs their machines an hr per week during the season like many homeowners do....
 

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A lean running two stroke doesent sieze by lack of oil, they seize because of elevated burn temperature and the fact that the slower
flame front still burns when the exhaust opens. ( this is very similar to burnt exhaust valves on a four stroke but with greater damages.)
For us who ride snowmobiles and uses straight fuel, oil comes from a separate tank and is injected by a metering pump.
- you can shut the fuel completly of and the Engine will still get the appropiate amount of oil for a given load ( rpm/ throttle position )
First run of the season is the check for a beginning of a fuel problem test run.
- Tumb to the steeringbar, let it run wot for 1000 feet or so... shut it down quickly, read the plugs..anything lighter than medium Brown is a sign.
- a White plug, continue running and you will either have a hole in the piston or a seized cylinder. Often both.
Note that they can also "lean seize" at lower throttle positions than wot, im Always weary about midrange bogs and such.
 
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