Closing Throttle Beneficial During Long Cuts?

[max2cam]

Say I'm making a long sustained cut -- either milling or sawing up a big log. Is there any cooling/lubrication advantage to closing the throttle periodically and then resuming the WOT cut?

Of course one would take the bar out of contact with the wood when doing this so there is not a heavy load when going back to WOT.

The reason I bring this up is for two reasons: 1) The first time I ever used a chainsaw was a rental unit and the guy told me to throttle down like that while cutting. 2) In old Harley-Davidson operator manuals it says the same thing: To periodically close the throttle when running at high speed to draw additional oil to the piston and cylinder.

Would this also be true when running a 2-stroke chainsaw engine? Throttling down in long sustained cuts would draw cool fresh charge around the piston plus a momentary break of the hot combustion process?

I'm not saying this is true or a good practice, but wondering what you guys think...

 

[Oregon_Rob]

I can’t answer your question regarding the impact to the saw, but when milling, it is preferable not to stop the cut and restart. When ever you let up on the cut, you screw up the surface, it becomes inconsistent. I have recently made some benches for a camp fire ring and on one I back up and it is a very obvious flaw.

 

[tony marks]

one mechanic told me that the most lub is on the l side. as far as full throttle ..
the oiler would be one reason, i would let up off an on...these things sometimes turning 13000 14000 ... got to believe its better not to just leave it wide open ,like a 4 cycle,can be run..

 

[crowe]

I have been cutting for twelve years and have never worried about how I was holding the throttle. You just need to make sure your saw is not over revingin the cut. I squeeze the trigger just enough to get the jod done I dont use any more power than I need.......Wade

 

[Rotax Robert]

Run it wide open, short of having a very dull chain and causing the engine to over rev or having a suped up engine you should never have a problem. That being said, I always let my saw sit and idle a short time after a long hard pull through the larger wood or where I feel I have worked my saw hard. Remember, your saw has only two cooling sources...air and oil.
Air does'nt conduct heat very well and your mix is your only other source of lube/cooling.

 

[glens]

I can't speak of all current saws, but it's my understanding that current stuff doesn't have sophisticated carbs like they used to.  Idle and high speed circuits only (or for the most part?).  Refer to Russ' excellent post in "MS 460 stuck rings?" from the other day.

We had an 029 that would reliably "die" just like it ran out of gas, but only for one user while limbing.&nbsp; It worked perfectly (yes, they <i>can</i>) for everyone else.&nbsp; It turns out, after dinking with the fuel vent, filter, impulse hose, and going through the carb, that it still happened for him, who was using it part throttle a fair portion of the time.

I'm so used to letting an engine idle for a few moments before shutting it down that I never have understood why some people rev their (car) engine just before doing so.

Glen

 

[cbfarmall]

Glens:

This is a guess, but a good one I think. Lots of old habits carried over from carbureted vehicles, such as pumping the gas to get her started. Sometimes if you let a carb. engine idle too long it'll load up with gasoline. I'm guessing that goosing the engine before killing it is a way to clear out the gas so it doesn't wash down the cylinder. If I'm wrong somebody will shoot me down.

Chris B.

 

[bwalker]

By letting off the throttle mid cut you are efectively cutting the lubricant when your engine needs it most. If I where milling I would run 32:1 and richer than normal carb settings.

 

[tony marks]

let me clearify ... when i said let off throttle ,mid cut ,i also take it outa cut. mostly to try an get oil to the chain... just dont let it stay in cut if shes not putting out chips,as it cant be doing the wide open saw no good. jmo

 

[Crofter]

Originally posted by glens
[I'm so used to letting an engine idle for a few moments before shutting it down that I never have understood why some people rev their (car) engine just before doing so.

Glen [/B]

A lot of cars in the 60's and 70's would run on after turning off the ignition and refuse to shut down. Giving a burst of throtle just before turning off ignition would usually allow the combustion chamber surfaces to cool enough while coasting down, to prevent run on. I think this is where the habit comes from. It sure is a bad thing to do with a turbo engine though.

Frank