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Old 07-07-2013, 05:01 PM
diyer999 diyer999 is offline
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Full RPM or just what is needed to do the work ?

There is this ongoing debate among local shops, landscapers, repairmen all telling me two opposites as the correct way to run two cycle outdoor power tools, to ensure long life and fewer problems. To add to this uncertainty, I have two manuals of the same brand of equipment, and each manual says the opposite of the other one.

So, the first theory is that all two cycle outdoor power equipment is designed to run at full throttle. A friend of mine who is an automotive mechanic said that makes the most sense when it comes to running a chainsaw. He has no opinion about string trimmers, hedge trimmers, blowers, edgers, etc., and I'm wondering if the type of tool determines how much throttle should be used. Does it vary by tool type? For example, my string trimmer manual say to operate the tool at full throttle, 7,800 rpm. On the other hand, the same brand of hedge trimmer I have says to only use the amount of throttle needed to do the work. The string trimmer is 10 yrs old, the hedge trimmer is a 2012 model . . . not sure if that decides the matter. It seems that most of the two stroke/cycle repair-technicians I ask about this say to only use what is needed to do the job. It is mostly the salesmen that side with the full throttle theory.

Why is it important? To ensure long life with fewer problems. Those for the full rpm theory say if that if the tools is not run at full rpm it will form carbon deposits much quicker, and develop all the problems associated with that buildup much sooner than later. The lower rpm guys say that the engine will run cooler and last much longer. Both theories make sense.

I prefer to use less power as long as it gets the job done because at full throttle my string trimmer screams and neighbors complain. So, I have to be careful when I run it, so as not to violate the local noise ordinance (its always something).
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Old 07-07-2013, 05:26 PM
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I could really care less about how long the equipment lasts because in my opinion, you're not going to notice much of difference. I just use enough to do the job, sometimes a little heavy. Chainsaws I typically do run full throttle, but yet again, that's generally out of necessity.
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Old 07-07-2013, 05:46 PM
locallawncare.ca locallawncare.ca is offline
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I think the main thing is not to constantly rev them, try to keep a consistent throttle, I always hear people using backpack blowers by just quickly squeezing and letting go of the trigger, I'm no mechanic but that's what I think on the subject.
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Old 07-07-2013, 09:26 PM
turfmd101 turfmd101 is offline
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I say only use whatever it takes as to not strain or bog the engine. I think any engine run high throttle without enough load will likely cause excessive engine heat which causes ware. Just my opinion. It's my understanding that heat is any engines worst enemy.
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Old 07-07-2013, 10:05 PM
vertigo01 vertigo01 is offline
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Quote:
Originally Posted by diyer999 View Post
I have two manuals of the same brand of equipment, and each manual says the opposite of the other one.

For example, my string trimmer manual say to operate the tool at full throttle, 7,800 rpm. On the other hand, the same brand of hedge trimmer I have says to only use the amount of throttle needed to do the work. The string trimmer is 10 yrs old, the hedge trimmer is a 2012 model . . . not sure if that decides the matter. It seems that most of the two stroke/cycle repair-technicians I ask about this say to only use what is needed to do the job. It is mostly the salesmen that side with the full throttle theory.

Why is it important? To ensure long life with fewer problems. Those for the full rpm theory say if that if the tools is not run at full rpm it will form carbon deposits much quicker, and develop all the problems associated with that buildup much sooner than later. The lower rpm guys say that the engine will run cooler and last much longer. Both theories make sense.
(its always something).
I am new to the site however internal combustion engine's work the same way.
These are my thought's.
Think of it like an outboard motor, you have the same 2 outboard engines with exactly the same HP rating's, gear ratio and with a max RPM of 5500 on exactly the same boat's.

The only difference is.
Motor 1 has a 17" pitch prop
Motor 2 has a 21" pitch prop
Motor 1 turn's max RPM of 5500
Motor 2 turn's max RPM of 4700

Now both motors get the job done but motor 1 does so more efficiently ( staying in the torque curve ) than motor 2 due to the fact that motor 2 is lugging ( bogged down ) due to the reduced gear ratio of the larger propeller which in turn WILL cause the engine to carbon up ( not running within specified torque curve ) and reduce it's longevity overall because it is being overworked.

Hope this help's.
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Old 07-07-2013, 10:43 PM
windflower windflower is offline
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To reduce the noise I use just enough throttle. My current trimmer (echo) must have 4000 hours on it by now. It is at least 10 years old, used daily. I've never had carbon problems since switching to stihl oil.
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Old 07-08-2013, 11:48 AM
diyer999 diyer999 is offline
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Thank you, all the answers were great. More are welcomed. I am always just so stumped as to why the retailers of the handheld outdoor power tools consistently tell me that those tools were designed to run at full throttle, regardless of how many times I question their logic, mentioning the increased heat, wear and tear issues. As I said, their argument is that lower throttles produce more carbon by bogging it down and that does also make sense. But they are specifically saying "full throttle" and to me there is a big difference between full and efficient or consistent. However, I never really pressed them for their definition of full, and it maybe that they mean more than enough throttle off and on, or something like the one post said full for a second or two, or keeping it consistent. Communication among people is not always what is intended or what seems to be.
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Old 07-08-2013, 12:37 PM
Pierre2013 Pierre2013 is offline
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Quote:
Originally Posted by turfmd101 View Post
I say only use whatever it takes as to not strain or bog the engine. I think any engine run high throttle without enough load will likely cause excessive engine heat which causes ware. Just my opinion. It's my understanding that heat is any engines worst enemy.
It is fascinating that both, engines and electric motors have the two same ennemies: dust/dirt and heat.

To the OP: as stated before; higher RPM means higher internal heat and increased friction wear. You run a chainsaw at full speed because you need the cutting power, not because it is beneficial for the engine (though it can be argued that full RPM is beneficial in this case for the engine as lower RPM would lead to the engine running for a longer period of time and would increase internal temp of engine even further). Run trimmer at lowest needed speed.
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Old 07-08-2013, 04:09 PM
timgren timgren is offline
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Quote:
Originally Posted by windflower View Post
To reduce the noise I use just enough throttle. My current trimmer (echo) must have 4000 hours on it by now. It is at least 10 years old, used daily. I've never had carbon problems since switching to stihl oil.
I agree with using "enough" to get the job done efficiently. Do you need to push full thottle on a chainsaw if the work is only to trim off a 2" branch? One brief rev could do that job. Of course if equipment were to be run at full throttle the entire time, there wouldn't be a need for a variable speed throttle at all. Just an on-idle-off switch. Right?

If the goal is to ensure long life and fewer problems, then in my opinion, this comes from proper maintanence, using quality parts, and good fuel. In my experience, "cheaper" is almost always the most costly option in the long-term. Now, i do admit I tend to go over the top and am often mocked by friends and family. Such as using 91 octane fuel in all my small engines, pure Mobil-1 oil and grease, Champion all-copper plugs, etc. But these same friends are the first to call when they need to borrow something - and every one of my engines start on the first pull even after sitting cold all winter. The blades are sharp and ready to go, and the equipment is kept reasonably clean. Too me, this ensures long-life far more then throttle speed.
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Old 07-08-2013, 05:40 PM
diyer999 diyer999 is offline
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Quote:
Originally Posted by timgren View Post
. . . Of course if equipment were to be run at full throttle the entire time, there wouldn't be a need for a variable speed throttle at all. Just an on-idle-off switch. Right? . . .
THAT is a very logical point.

I have a string trimmer that I have been using lightly (1 hr every ten days, from May thru late Sept) and trouble free for ten years, until last year, when it shut off from carbon clogging. Since I never used the full throttle theory, I got to wondering if the clogging happened as a result of my babying the tool -- I never really pushed it much, maybe even under revved it. Perhaps that is what happened. At any rate, I suppose that is what got me concerned. When I pulled the muffler off, sure enough, the screen was completely blacked shut with carbon. I think there is still some on the piston rings, because when it gets hot it still shuts down, even though the screen is now clean.
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