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Tuning up a Husqvarna 50 chain saw. Idle set, L set but when you adjust H manual says to make sure it's "four cycling" as you turn the screw. By ear, I get it where it sounds good but not sure that's what they want. The manual has a bold face warning that failure to achieve this mixture adjustment may cause piston seizure. Anyone know what they're talking about?
 

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They are saying dont lean it out to far or you will seize the saw. The true correct way to set the carburetor is with a tach. But if you dont have one what they are saying is do the base settings on the carburetor then from there adjust the high speed adjustment on the carb by ear with the saw running at max throttle to when the saw sounds like a 4 cycle motor when you get this sound you are set . Just remember if you go to far you can and will lean the saw out and may cause damage, if you go to little and run it rich you take the chance of fouling the spark plug,building carbon etc and can produce other running issues.
 

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Tuning up a Husqvarna 50 chain saw. Idle set, L set but when you adjust H manual says to make sure it's "four cycling" as you turn the screw. By ear, I get it where it sounds good but not sure that's what they want. The manual has a bold face warning that failure to achieve this mixture adjustment may cause piston seizure. Anyone know what they're talking about?
What this means basically, is to adjust it where it sounds like it's running really smooth. Then back the adjustment screw out a little until it just begins to sputter a little. Of course if you have a tachometer, that's the way to go as rotti suggested.
 

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Ok, now someone explain to this old country boy how a tach is going to tell me when I have the mixture rich enough. If I have a 2-cycle screaming about 9500rpm at WOT is 9300 or 9400 going to be rich enough, but then it could be only 7500rpm because of an air leak then it would need a more rich mixture on the carb to compensate for the leak. Have a good one. Geo
 

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Ok, now someone explain to this old country boy how a tach is going to tell me when I have the mixture rich enough. If I have a 2-cycle screaming about 9500rpm at WOT is 9300 or 9400 going to be rich enough, but then it could be only 7500rpm because of an air leak then it would need a more rich mixture on the carb to compensate for the leak. Have a good one. Geo
If you have an air leak, you need to fix it. You cannot compensate for an air leak somewhere in the crankcase by adjusting the carburetor and have the engine run correctly. The reason to use a tachometer is so you do not exceed the max rpm the engine is designed for. Too fast and oil will sling off the bearings on the connecting rod and you will have damage regardless of the mixture.

Of course if you have calibrated ears, then you can tune it correctly by ear!
 

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30year;
You are starting to sound grouchy, spring is just around the corner. Have a good one. Geo
Around the corner??

Spring is here, at least in my part of the country...

I am sorry if I sound grouchy, I thought I was just answering your question.
 

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If you have an air leak, you need to fix it. You cannot compensate for an air leak somewhere in the crankcase by adjusting the carburetor and have the engine run correctly. The reason to use a tachometer is so you do not exceed the max rpm the engine is designed for. Too fast and oil will sling off the bearings on the connecting rod and you will have damage regardless of the mixture.

Of course if you have calibrated ears, then you can tune it correctly by ear!
Really? Sling the oil off the bearings? Like 7000rpm won’t do that but 9500 will? First it depends on the size of the air leak. Sure some leaks can be compensated for with the mixture but there is a limit of course. What ruins the engine is the mixture not oil slinging off of the engine components. As you lean the mixture the engine rpm increases dramatically which makes one think the engine is running better but in fact the lean mixture doesn’t provide enough lubrication so you wind up with an engine running at a dramatically higher rpm without enough lubricant as the engine depends on the oil from the gas/oil mixture for lubrication. a rich mixture provides more lubricant and slows the engine rpm because it can’t burn the rich mixture as efficiently as a lean mixture. Just the nature of a small two cycle engine.
 

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Really? Sling the oil off the bearings? Like 7000rpm won’t do that but 9500 will? First it depends on the size of the air leak. Sure some leaks can be compensated for with the mixture but there is a limit of course. What ruins the engine is the mixture not oil slinging off of the engine components. As you lean the mixture the engine rpm increases dramatically which makes one think the engine is running better but in fact the lean mixture doesn’t provide enough lubrication so you wind up with an engine running at a dramatically higher rpm without enough lubricant as the engine depends on the oil from the gas/oil mixture for lubrication. a rich mixture provides more lubricant and slows the engine rpm because it can’t burn the rich mixture as efficiently as a lean mixture. Just the nature of a small two cycle engine.
Like anyone wants my opinion on a 10 yr.old post. Years ago, the RedMax service manager at that time, Andrew Kuczmar, personally provided regional training. He used to work for Mercury Marine racing decades before, with 2-strokes. He stated a 2-stroke has to go about 18K before con-rod lubrication becomes an issue. I have no reason to doubt him.
That being said, a STIHL MS200 turned about 14,300 by spec. with chain (would actually turn about 15,300 no-load). And RedMax CHTZ2450 RPM rev. limiter was set at 12K, as was a STIHL MS201T (originally), then it was changed to 13K. And, Yamaha had a GP engine in 1968 that turned 17K.

Andrew referred to a book as the Bible in 2-stroke, because of the research that went into it. I have a copy of this, it makes for interesting reading as a lot of the research was done by manufacturers such as Yamaha and McCulloch. 2 Stroke Tuners Handbook: Jennings, Gordon: 9780912656410: Amazon.com: Books

BTW, Andrew is still with RedMax: https://www.linkedin.com/in/andrew-kuczmar-9b315164

Just chiming in...
 
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