How long can you keep the throttle wide open without load?

[Husky77]

Its very easy to set a carb if your shown by the right person to begin with, a tach is handy but when you understand the high needle and four stroking you'll find it will be pretty spot on with revs. But dont forget the low needle, they work like a married couple and if not set right you'll be pulling your hair out

 

[Hulpio]

Its very easy to set a carb if your shown by the right person to begin with, a tach is handy but when you understand the high needle and four stroking you'll find it will be pretty spot on with revs. But dont forget the low needle, they work like a married couple and if not set right you'll be pulling your hair out

Any advice where to look for that L needle on a average wife? Mine for sure needs some leaning.

 

[Husky77]

An apprentice tech.

Tachometer, rev counter

 

[HansFranz]

Someday I'll be confident enough to tune by ear.

I suspect that day will come around the second or third time you use the tach. I think I used mine maybe twice to set the H screw.

As for setting idle speed, if the chain moves, it's too fast, and if it stalls, it's too slow.

YMMV.

 

[Husky77]

I suspect that day will come the second or third time you use the tach. I think I used mine maybe twice.

That's probably right, there used to be a guy working at my local dealer who was happy to take the time and show & explain. He set a saw once and said its 12500 rpm, I laughed and said show me so he dug out the little tach and sure enough he was spot on. Amazing but when your doing it all the time your ear gets tuned in and it comes easy. It was a great little family dealer always had time for you, then as the father and mechanic got older (my age haha) the son took over and he is all about money and dont care. Sad to see because it was built up from nothing, everyone went there but now it's mostly sell a mower and service it £€£€. They were forestry workers so knew evering aspect, the son never don a days work in his like.

 

[HansFranz]

That's probably right, there used to be a guy working at my local dealer who was happy to take the time and show & explain.

Yeah, after I bought my Frankensaw 660 (hybrid of Chinese and OEM parts) and ran a few tanks through it, then modded the muffler, and then re-tuned it (the builder had set it pig rich when he shipped it to me), I took it to my local Stihl dealer and asked him to check my tune. He started it, and warmed it up, and revved it a few times, and said, "That's exactly where I would tune it, too."

 

[Breckinridge Elkins]

Let's say an experienced mechanic tuned a carb perfectly and recorded the RPM's. Could you then use a tach to retune to those RPM's whenever environmental conditions changed? I suspect the answer is "not necessarily" but I am curious to hear from experts.

 

[Gratewhitehuntr]

@Husky77 worse to let them idle and get all carbon'd up, than to rev and burn clean.

I ran a whole tank of fuel through a ported WT at WOT, trying to get it to boil fuel again.
She's a screamer. Sorry, no tach. 17k? Moar? OK!
That's the only reason I'd use one, for braggin. Probably 18k but, we'll never know
Thought about buying one, many many gallons of fuel ago. Meh. Been tuning by ear so long now. Why would I care what the factory rpms should be, if my modified (whatever) out-cuts factory by 30%? OMG slightly rich... oh noes!

Anyone notice how changing bar length or chain type can result in sub-optimal tune?
I see it in the chyna660, switching from 20" to 32" works best with a slight retune.

 

[Gratewhitehuntr]

Let's say an experienced mechanic tuned a carb perfectly and recorded the RPM's. Could you then use a tach to retune to those RPM's whenever environmental conditions changed? I suspect the answer is "not necessarily" but I am curious to hear from experts.

Isn't repeatability the entire idea behind measurement devices like a tachometer or micrometer?
I thought the Mtronic was basically tuning by rpms. No? Yes.

 

[HansFranz]

I ran a whole tank of fuel through a ported WT at WOT, trying to get it to boil fuel again.
She's a screamer. Sorry, no tach. 17k? Moar? OK!
That's the only reason I'd use one, for braggin. Probably 18k but, we'll never know

If it's moar RPMs you're after, leaning it out will definitely get you there. I guess the only caveat is that it'll burn up your motor...

 

[rogue60]

Let's say an experienced mechanic tuned a carb perfectly and recorded the RPM's. Could you then use a tach to retune to those RPM's whenever environmental conditions changed? I suspect the answer is "not necessarily" but I am curious to hear from experts.

Yeah I'd like to know how tach tuning to factory specs is any good when they say elevation and weather temperature different loads dull or sharp chain all effect tune.
I've never used a tach for tuning I don't get it surely a saw won't tune the same for every scenario some guy's say they are tuning all day for different temp swings for example.
Tuning to factory specs with a tach is sloppy tuning if you ask me maybe someone who does will chime in and let us know tuning like that is perfect no matter the conditions. And surely a ported saw will tune different to a epa choked up stock saw?
Idk I reckon throw the tach and factory specs seems lazy and not a very efficient way to tune a saw like they say Mtronic or Autotune is tuning constantly while the saw is running yet some say tune to basic factory specs no matter what is the only way to tune like I said I don't get it lol

I just broke in a new bit of o p e gear (Stihl) it needed more fuel after the rings seated I had to cut the limiters to achieve this there wasn't enough adjustment from the factory the idiots lol

 

[Hulpio]

If do get a chance if will attach extension to the H screw of my old Husky 340. The plan is to measure diameter of the screwhead, find something in same diameter and use glued hose as a joint between. Ideally this should be done before I cut a couple of birches from my yard. One of my 3 sons will have honors to be saw operator when daddy is dialing in max power. From that setting I will go tiny bit to the rich side. It will be interesting to see how husky then sings without load, if any 4 stroking is there or not.
Installing EGT gauge and quick connect WB O2 sensor would be optimal I guess but I've heard that food ain't so delicious in mental hospitals

 

[Old2stroke]

Tach tuning is for repair shops and others that don't mind placing their blind trust in numbers provided by manufacturers whose main concern is emission standards and not the longevity of your engine. Unfortunately, it's not possible for many shops to maintain a store of logs for saw testing and many of them that aren't saw dealers have mechanics that mainly work on 4-stroke things like lawnmowers and snowblowers, don't actually use chainsaws and wouldn't know what to do with a log if they had one. A good shop with experienced saw mechanics will take the factory rpm specs with a grain of salt and tune a little lower, especially if setting up a new saw. A good mechanic that doesn't want to fool around with a tach, might just set the high speed rpm by ear to the point where it is obviously 4-stroking. A mechanic that never uses a chainsaw might set the high speed rpm to the point where it is running crisp and clean WITHOUT 4-stroking. Get it running, get it screaming, get it out the door, get on with the next job.
If you are going to own chainsaws, do your own repairs and do any serious cutting, learn to tune by how the saw sounds in and out of the cut.

 

[NSEric]

Let's say an experienced mechanic tuned a carb perfectly and recorded the RPM's. Could you then use a tach to retune to those RPM's whenever environmental conditions changed? I suspect the answer is "not necessarily" but I am curious to hear from experts.

I did this on my ported saws as factory rpms mean nothing on them.
I taped the tach to the saw and cut up some large wood tuning the saw for max rpm under full load, then I checked max rpm no load.
If I want to, I can set the saw to the new max rpm quickly when the weather changes but I kinda gave up on the tach and do it by ear most of the time now tho. My joncutter 5800 likes to be set at 14500-14800rpm lol.

 

[Gratewhitehuntr]

If it's moar RPMs you're after, leaning it out will definitely get you there. I guess the only caveat is that it'll burn up your motor...

Moar than what? Moar than it can handle? Apparently not. Despite repeated overheatings, the rings and cyl are still ok.
I was looking at this early WT porting massacre a couple days ago, trying to decide if it should go on the wall or in the scrap.

IMHO, YMMV, IANAL, controversial claim here, stand back!
A tachometer is not much more than an idiot light with numbers.
If I had one, doubtful I'd trust it over my own ear.
That stupid tach isn't gonna rebuild my saw, who made it the boss of me?
Nope!

@Husky77 I think the idea that revving without load is bad, comes from flat bearing engines. In that case, yeah sure.
Could you could explain to us, what you thought might go wrong?
Serious question. I'm curious to hear the idea why revving without load might be bad.

 

[Vintage Engine Repairs]

A tach works well and gets you close, if in doubt go a bit richer. Tuning by ear is great if you know what you are listening for. It’s not until it’s under load and you can feel how the engine is responding, especially when it’s at operating temp that you can really know where you are though.

I’ll set it by ear, confirm with a tach if I have specs and then when it’s fully heat soaked I’ll see / feel / listen for to how it responds, I’ll go a bit leaner or bit richer and see if it improves. When it’s at its peak performance I’ll richen it up just a bit for a bit of a buffer for hot days, dull chain, shorter or longer attachment / bar.

 

[lohan808]

I do the following even on my ported saws.
1. I set the idle flap and h/l jets to 1 turn rich from full seat. Warm them up and get the chain to stop spinning and idling at about 2.5k to 3k depending on the cc size. Yes I look at a tach after I get my ear in it.
2. Now I go after the high jet looking for the 4 stroke at no load. Not stumbling at WOT but not quite dancing on the limiter either. Drop it in a log and make the last few fine adjustments. Tach can be referenced here but really with the ported stuff it doesn't make a lot of sense. It usually turns out that RPM is 500 to 1k over factory recommendations anyway.

 

[HansFranz]

Despite repeated overheatings, the rings and cyl are still ok.

I'm curious how you know it repeatedly overheated if the rings and cylinder were OK.

Just trying to learn here...

 

[Gratewhitehuntr]

I'm curious how you know it repeatedly overheated if the rings and cylinder were OK.

How can I tell things are hot? Well if it was an outboard, they make crayons.
No, that's not sarcasm. Temp crayons. Yes, you can eat them cold too.

Short answer, it liked to boil fuel.
When I ported that (free trashpicked saw) I had NO IDEA what port timing was, porting was only experimenting to see what would make one rev (just make all the ports YUGE!) and I think the intake duration was messed up enough to pre-heat the carb, whatever the reason, it would boil fuel if you shut it off. Once cooled off it would restart and rev high enough that I wondered, for the first time, if it was possible for the crankshaft to come out and hit me. Haha I still kinda wonder this sometimes.

I'm de-Poulan-ing the shop attic. Ring and cylinder finish? Wow it's... not ruined? Port timing? WTF? Yeah, it's ruined
This is the sort of stuff that gets a casual glance, like a picture of the chic you were in looooooove with at 14yo. Meh. meh...

 

[david newbie]

Moar than what? Moar than it can handle? Apparently not. Despite repeated overheatings, the rings and cyl are still ok.
I was looking at this early WT porting massacre a couple days ago, trying to decide if it should go on the wall or in the scrap.

IMHO, YMMV, IANAL, controversial claim here, stand back!
A tachometer is not much more than an idiot light with numbers.
If I had one, doubtful I'd trust it over my own ear.
That stupid tach isn't gonna rebuild my saw, who made it the boss of me?
Nope!

@Husky77 I think the idea that revving without load is bad, comes from flat bearing engines. In that case, yeah sure.
Could you could explain to us, what you thought might go wrong?
Serious question. I'm curious to hear the idea why revving without load might be bad.

I'm pretty much stuck with tuning by tach, as I can't hear very much, and I'm not willing to lose more hearing by running my saw with my hearing aides on. Unless one of you guys wants tp come to southern oregon and help me?