Reason for idle speed spec?

[mike-s]

I understand keeping idle speed well below the clutch engagement speed. Also, that it can have an effect on acceleration to full throttle. But, beyond that, why is there a spec? With small engines, I typically set them to idle as low as I can where it idles reliably without the engine dying out. Is there a reason not to?

 

[cus_deluxe]

i typically try to keep my saws idling just below clutch engagement speed.

 

[Joab]

I've got a little tach -- not a pro model, but reliable enough. I've tried setting them to spec for idle where I can, but in some cases (and it seems to be on well broken-in saws), the spec is too slow and it idles a little more reliably if you run it a bit faster than that.

Partner had a blurb in their manual for a P5000 that basically said to set the saw to idle below engagement and as low as you can where it still idles (like you said), but then test it by turning the saw on its side and back upright quickly (maybe a few times). If changing the orientation of the saw quickly brings it close to stall then its too low.

If the spec is too slow to idle reliably, or I don't have the spec, I use Partner's test. Ideally that's just enough below clutch engagement that you don't have to fine tune every time the weather changes. ( I think that guys who know their saws and have been using them for years have a pretty good sense of where that is without so much thinking -- for me, I find the Partner test helpful.)

 

[Huskybill]

Remember these are air cooled even while idling. Less rpm, the more it can heat up.

 

[grizz55chev]

Remember these are air cooled even while idling. Less rpm, the more it can heat up.

If your saw is hot while idling, you have other problems, don’t ya think?

 

[Joab]

I understand keeping idle speed well below the clutch engagement speed. Also, that it can have an effect on acceleration to full throttle. But, beyond that, why is there a spec? With small engines, I typically set them to idle as low as I can where it idles reliably without the engine dying out. Is there a reason not to?

I guess I gave my 2 cents on how to tune idle speed but maybe that wasn't your question.

My understanding is that climate and altitude affect how a saw runs -- I think the idle spec is supposed to give a saw mechanic at a dealership with a good tach a quick way to double-check the factory tuning for their particular location before sending it out the door to a customer. On new saws, tuning to the spec is probably reliable most of the time.

The good reasons to ignore the spec are if you don't have a (reliable) tach or if the spec just doesn't deliver the intended result. [ I suppose, though, that if the spec doesn't produce a saw that idles reliably, it's probably a good idea to check the fuel system and air filter for problems.]

I'll note that I'm not a dealer or a professional mechanic and I only work on my own saws for the most part (and the only newer saw I've got is an autotune).

 

[RED-85-Z51]

On a 4 stroke without pressure lube...they rely on the dipper or splasher to sling the oil into a mist and lube the internal components...idle too low and you start to starve upper main journals on vertical shafts and valve train components on ohv engines...

Sent from my LM-G820 using Tapatalk

 

[mike-s]

i typically try to keep my saws idling just below clutch engagement speed.

Do you have a reason for that? I set lowest reliable idle for less noise, less gas use, less exhaust.

The good reasons to ignore the spec are if you don't have a (reliable) tach or if the spec just doesn't deliver the intended result. [ I suppose, though, that if the spec doesn't produce a saw that idles reliably, it's probably a good idea to check the fuel system and air filter for problems.]

So, in brief; do what works?

 

[Joab]

Do you have a reason for that? I set lowest reliable idle for less noise, less gas use, less exhaust.

So, in brief; do what works?

I'm not always good at brief. . . But, yes, exactly!

 

[KASH]

Every saw idles a little different I set them as low as possible.I have old outboard motors that troll all day long so slow you can almost read the writing on the flywheel starter rope plates.As for 4 strokes my Ford 8n tractor idles at 275.My old Lister generators set at 450 rpms constant with a life time expectancy of 40,000 hours,
In my opinion your will never cause engine damage to a 2 stroke by low idiling provided you have sufficent oil in your mix.
Kash

 

[cus_deluxe]

Do you have a reason for that? I set lowest reliable idle for less noise, less gas use, less exhaust.

i find that its easier to tune the low at a little higher rpm. lower rpm, easier for it to load up if it sits idling for 10-15 seconds. ymmv

 

[drf255]

I only use a tach for idle speed when I can’t get it to idle without clutch engagement. Otherwise I do what Custer does.