Tach

[Treeaddict]

I’m looking for a tachometer and I’m confused. Most of the ones I see have wires that you have to wrap around the plug wire or require foil tape for use. All the videos I see show someone holding the tach close to the motor only. This is the type of want to purchase. What are you guys using?

 

[Dave Shepard]

Mine is a Tech Tach, Tiny Tach, TT20, or some combination of that. It's the only one that refreshes fast enough, .5 seconds, for chainsaws.

 

[Dave Shepard]

 

[pigwot]

That’s the one I have. They’re not expensive snd quite helpful. Found I needed it as my hearing started going (likely just fooled myself that I could ever truly ‘hear’ the perfect tuning up till then). Some saws I could feel/hear when they were spot on: 266, 281. Others I definitely needed the tach, like the 346

 

[Raj]

I think I have the Echo PET 304. I like it. Wireless or wired.

 

[Maximalist]

I have an EDT 7 tachometer. It works on a contact and non-contact circuit. However, the manufacturer recommends using a contact diagram.

 

[Trains]

Do the saws you want to check have limited coils, if so, you need to factor that in, like the stihl edt7 on wards read limited coils.

I have an oppama
PET-2000DXR

OPPAMA | Engine tachometers

Oppama Industry is a company that develops, manufactures and sells engine ignition systems, gear heads for brush cutters, brush less motors, engine tachometers,

www.oppama.co.jp

it reads fine without the wire, just place it near the sparkplug on the top cover, and it reads it easily, but it dosent read limited coils, just shows garbled numbers when the limiter kicks in.

 

[Treeaddict]

I actually have no idea if they have limited coils. Mostly because I don’t know what they are !

 

[Trains]

Some coils will limit the max rpm by cutting spark so the saw wont over rev, pretty much most new saws have them now.
Unlimited coils require the correct mixture on the H jet to limit the max rpm.

So tachs that cant read the limited coils will show a garbled reading once the limiter starts working, where as the tachs that can read a limited coil, will show you an accurate reading when the limiter is working.

 

[Marc-Antoine]

I guess that they either take an average value on a larger period of time or they discard the out of range values (like accepting them only in a window around the most frequently readed instant values).

 

[Treeaddict]

I ended up with a Tiny Tach. All the recommendations were good but the Tiny was readily available and fairly inexpensive. I used it today on the 450 Rancher. Revved to 11000 upon startup and when warm was at 9000 and 2500 idle I believe. Right on the specs. I figured it would be a good idea to test all my saws.

Edit: I suppose they rev higher before warming up?

 

[Magnus]

What rpm is max power output in those specs you read?
In the info I have the max power output is 9000rpm. Idle 2700...
11 000 in WOT without load sounds a bit low.

Regardless of specs I try to set them so they run and perform its best.

 

[Trains]

I ended up with a Tiny Tach. All the recommendations were good but the Tiny was readily available and fairly inexpensive. I used it today on the 450 Rancher. Revved to 11000 upon startup and when warm was at 9000 and 2500 idle I believe. Right on the specs. I figured it would be a good idea to test all my saws.

Edit: I suppose they rev higher before warming up?

Hmm, I would not go wide open throttle on a cold saw, not good for it at all.
let it warm up, same with letting it cool off a bit after long cuts, dont just stop it after its been working hard, let it idle for 20 or so seconds to let it shed some heat, its good for the coil and the piston.

Agree with what Magnus mentioned, 11k seems a bit low for wot, I would assume from other saws specs, you should be around 12500 or so + - 500 ish, but get the specs for the saw and go from there.

I use a tach to get me close, and then tune in the wood for good 4 stroking unloaded and clean in the cut.

 

[Treeaddict]

Maybe idle is a little low.

What is WOT an acronym for?

I only revved it 3 times upon startup to get 11000 rpm. Never did it before. Just looking for numbers to compare cold to warm. I’m anal about warmup and cooldown procedures. Generally, I start the saw, rev once to back down the rpm’s, put my chaps, gloves, and helmet, then go to work. Usually cooldown is 30sec to a couple minutes before shut down. Just depends on how hard it worked. Climbing saw is usually one here or there so I’m less stringent.

The specs came from Husqy’s manual. It is a “farm/ranch” saw so maybe a little lower RPM’s.

 

[stikine]

WOT is " wide open throttle" Mike.

 

[Trains]

The spec sheet is not showing unloaded max rpm, but where its max power and torque is under load from a correctly sharpend chain.

 

[Treeaddict]

The 9000rpm is in wood?!! I would have never figured that. All else ( drills, reciprocating saws, oscillating tools ) have no load speeds. Strange.

So I’m supposed to read wot rpm with the bar buried?

 

[Trains]

OK.
yes, the 9k ish or there abouts is what to expect when the saw is cutting. But dont mess with your H adjustment to get that when the saw is cutting, your just chasing your tail if you do.
Far too many variables to use that as help for tuning, ie how long is the bar, what type of chain, what type of grind, what type of wood, how thick is the wood, you see, far too many variables.

No, dont read wot rpm with the bar buried, wide open throttle reading is given with no load.

just set the chain to correct tension, warm up saw, then go wot to get a reading, ie dont pee rev it for any longer than you have to.

What your aiming to do is to set the max rpm no load to safe limits, the richness of the h setting is in effect an rpm limiter if you dont have a limited coil.

What the 9k ish rpm amount is saying thats where it gives its best torque for cutting, those numbers are just marketing value really, and not helpful for correctly setting the max unloaded rpm.

Now when you have a limited coil, ie a coil that limits the max rpm, you can lean out the H and the coil will limit the rpm, but your going too lean, and risk damaging the saw.
If you didnt have a limited coil, the saw would soar up to 15k or more depending on type etc, and thats not only an overspeed, but its too lean to provide a protective oil coating and cooling at that setting.

Most saws with limited coils have the sequence of richening up the H till its blubbering and 4 stroking below the limited coil speed, then turn it in leaner till it reaches coil limited speed.
ie
lets say the coil is limited at 13000rpm, so you adjust the H side and richen it up till your reading 12500ish, so the saw is now limited by the richness, not the coil, then lean out till your at 12950 ish + - 500 rpm, and you have set your rich limit, again, thats an example of a possible sequence for setting up a saw on a limited coil so your not running it too lean.
Best to find the correct procedure for your saw and follow that.

hope that makes sence.


here is a vid that shows an ms460 being tuned, it shows what rich, 4 stroking sounds like, and being too lean.

 

[Treeaddict]

Thank you for the detailed information Trains/Grant. 😃. I’m not sure why the high and low jet tuning is such a difficult concept for me. I’ve done the idles on a few saws just fine after a couple questions were answered here.
I’ve yet to hear the 4 stroking but can detect faster and lesser revs although I’m not sure what qualifies as too high (lean) or low. I think being tone deaf plays a major part. I’m jealous of those who can tune by ear. If I didn’t use a tach, there’d be no way for my ear to know something is off. Maybe that will come in time with purposeful listening. Last year, it was hard to decipher if the 2 stroke being run in a neighborhood was a chainsaw, weed eater, or blower. I used to have to pay attention to how it was being used to determine what it was. Now, it’s easier to ascertain. 🤷‍♂️

 

[lxskllr]

Pick a day when you have a lot of easy cutting. Tune the saw obviously rich, and go at the wood. Listen. When you get in the groove, you should start to perceive the 4stroking. The saw will 'feel' slow, and you'll tune into the 4stroke growl. Back the high off ¼ turn, and keep cutting. How does it sound/feel? If the growl's still there, back it off a little more. Continue til the growl is gone when the bar's in wood. You should begin to hear the difference between the unloaded saw and when the teeth are engaged. I'll leave to others for the best place to eliminate 4stroking. I'm not clear on that, and I think I'm probably leaving performance on the table for the added safety of a richer mix.

The sound to me is like a hotrod getting on the gas down a residential road(4stroke) vs a Japanese sport bike nailing the throttle(2stroke). Just some suggestions that worked for me as someone with a bad ear for tuning.

 

[Trains]

hey Treeaddict,
Just go back and re watch the video again and again, listen for the differences, you will begin to learn to discern the difference in sound, its there and clearly in the vid, you just dont know what the small differences are at the moment, so tune with the tach for now and go by the numbers, I think I mentioned 12500 to you earlier wot unloaded.
Dont worry, in time you will understand what your listening for and after a while you will be listening to saws and be able to hear if they are running rich or lean on high or low jets, and annoy everyone around you when you tell them LOL.

hey just saw your latest vid, nice smooth run there, good to see.

 

[SkwerI]

Also the smaller the engine, the higher the max rpm typically. My old Stihl ms200T's typically get tuned to about 13,500-14,000 WOT and 3000 idle.

 

[Burnham]

Such amazing machines...

 

[Trains]

little remote control aircraft engines spin up pretty high too, as with most other rc type toys