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what happens with 2-stroke in a 4-stroke valved engine?

r7000

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anyone successfully run a 2-stroke lean mix through a 4-stroke motor (lawnmower) and for how long, or did you have problems?
 

Ryan Browne

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I used to dump old mix into my gas tractors before I switched to diesel tractors. I'd have no concerns about running it in something cheap and simple like a lawnmower. Probably wouldn't put it in my Honda though.
 

RocketRoss57

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That's all I run in my JD walk behind. I always got a bunch of fuel from the boat and Im able to just pump it in with the in line bulb. Been doing it for years no issues. Same spark plug still too.
 

Fish

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When I worked at a shop/store and ran the show, all we has was fuel with 40:1 mix in it. Saved tons of money.....
 

Fish

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I worked at other shops that had 4 different fuel cans, for all of the possible variations, quite silly....
 

r7000

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here's the cumulative affect, this is on a gcv190 honda mower. exhaust valve in cylinder caked up and wouldn't seal, got flame out the exhaust on hot restart and died. Then wouldn't restart until cold. And then if i got it started it was with the carb mix screw out 4 turns and engine would only idle for 20 seconds until it got hot, could not give it any throttle or would die. had to pull entire engine apart on the gcv type to access the valve seats. the exhaust valve itself was mostly clean, the problem was the cylinder not the seat face but the outer lip just past the 30° or 45° angled seat where too much carbon built up preventing the valve from seating and sealing, the light valve springs in this kind of engine probably does not help either. less than 3/4 gallon of gas with hp ultra oil at 40:1 was used, which was then mixed again with regular gas in mower tank to make about 70:1 to 100:1 in the mower, never any smoke engine ran fine until the last restart.
 

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Dub11

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Wow. Now I'm running my mic through a clapped out Briggs. But I have heard of stihl ultra doing this in stuff like blowers and trimmer that dont get as hot as a saw would.
 

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I always dump old mix into the tractor or riding mower. I domt think a little lube in the fuel is going to hurt anything, I would say it adds a bit of welcome lubricity to the valve seats and faces similar to MMO and the like. It is always well diluted with straight gas in the tank and I've never seen any fouled plugs or valve problems from it.

I'm glad we are having this conversation, it reminds me I need to replace the fuel in my Dolmar 5105 and Echo 500P!
 

Wilhelm

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I noticed that when I ad 2-stroke oil into the tank of my 4-stroke walk behind mower (190cc, 6HP) the engine is noticeably quieter and the valves rattle less.
No noticeable loss in power, no excess smoke, no difference in starting behavior and throttle response.

I don't ever have old 2-stroke mix because I always only mix as much as I need at the moment.

I don't ever wanna miss the power this thing has.
On occasions I've been going through grass as high as the mowers engine block and the mower just keeps turning and spitting.
DSC07866.JPG
 

KZ1000

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Just bought a new Stihl trimmer, it's four stroke but requires two stroke fuel due to no crank case oil. It still has valves and sounds like a Ford eight N!
 

FergusonTO35

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Yeah, I'm glad we are talking about this. I went ahead and dumped the fuel from all my saws except the one I'm using right now. Good thing I did, two of them I havent used in awhile showed the oil dropping out of suspension.
 

Wagnerwerks

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So we can all see the moral of the story.... Diesel vws ftw! ;)
 

r7000

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Just bought a new Stihl trimmer, it's four stroke but requires two stroke fuel due to no crank case oil. It still has valves and sounds like a Ford eight N!

i don't understand this, on a 4-stroke the crankcase (below the piston) is separate from the intake system (air/fuel) which is separate from the combustion chamber (above the piston).

what model stihl trimmer?

i thought the "trend" away from 2-stroke was emissions and EPA, now going 4-stroke but still needing 2-stroke fuel/oil mix seems... contradicting.
 

huskihl

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i don't understand this, on a 4-stroke the crankcase (below the piston) is separate from the intake system (air/fuel) which is separate from the combustion chamber (above the piston).

what model stihl trimmer?

i thought the "trend" away from 2-stroke was emissions and EPA, now going 4-stroke but still needing 2-stroke fuel/oil mix seems... contradicting.
It's called a Stihl 4 Mix. They've been out for a few years.
@Keith Gandy may be able to shed some light
 

Dub11

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So i guess it still allows you move the powerhead in any direction or angle you want but it uses the valve train system for better emissions.

I have a true 4 stroke Troybilt weedeater and you have to hold it on a "level plain" or it become instantly unhappy.
 

KZ1000

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Mines a R91T I think, like a said it sounds strange due to the much lower rpm but does a good job power wise.
 

r7000

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Not sure i believe that YouTube vid animation by lawnmowerMecca on YouTube, would think the gas oil mix would have to flow to thru the crankcase then up the transfer slot to intake valve. Would like to know how piston down stroke does not pressurize and blow back out thru intake and carb, are there Reed valves?
 
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