Guide(s) to tuning saw before and after muffler mod(s)

[ADK_XJ]

I may just be doing a poor job of searching the forum but I've read numerous posts about the process of tuning a saw after the installation of a muffler modification (dual-port)...however, I cannot seem to find a thread that actually gives a guide or describes the process in depth. Any suggestions?

For context, I've just recently purchased a very clean Stihl MS440 but it has a DIY dual-port muffler setup that I am trying to decide if I want to keep and/or if the saw is appropriately tuned to that modded muffler. I'm a bit gun shy as I have previously made a mess of tuning my old Stihl 041AV some time ago and had to take it into a shop.

The one common thread I read is that people recommend using a tachometer until your ear is developed enough to know what's "right" in the low and high end. If I'm only looking to do this work occasionally, is a more simple / cheap tachometer OK as long as it goes until the 10k+ RPM range?

 

[cuinrearview]

There is no tuning "after a muffler mod", there's just tuning. Turn the L screw to achieve the highest RPM at idle, then turn it counterclockwise about 1/8 of a turn. On the high end, you want a slight break up or burble at WOT, that cleans up to a smooth even rev when the saw is loaded in wood.

A cheap tach is just that. If you want a tool you can trust you'll have to spend some coin. Oh, and you'll want one that goes quite a bit higher than 10k. Some saws rev north of 15k at WOT unloaded.

 

[ADK_XJ]

There is no tuning "after a muffler mod", there's just tuning. Turn the L screw to achieve the highest RPM at idle, then turn it counterclockwise about 1/8 of a turn. On the high end, you want a slight break up or burble at WOT, that cleans up to a smooth even rev when the saw is loaded in wood.

A cheap tach is just that. If you want a tool you can trust you'll have to spend some coin. Oh, and you'll want one that goes quite a bit higher than 10k. Some saws rev north of 15k at WOT unloaded.

Thanks, that makes sense for the most part but what does the acronym WOT stand for?Wide Open Throttle?

 

[vizette]

Thanks, that makes sense for the most part but what does the acronym WOT stand for?Wide Open Throttle?

Yep - follow up to cuinrearview's post, L might need to be touched up again after you get high set. If you ever watched a buckin' billy ray video, you can clearly hear his saws do what he is describing. They sound pretty rough (a.k.a. four stroking) before he starts cutting, but as soon as he puts them to work, they clear up and purr in the cut.

I've found that newer 2 strokes in general with rev limiters are tricky though. You can't do the "lean until smooth and then back rich until burble" thing. I had this with a couple string trimmers I was working on - could not for the life of me get it to tune properly (so I thought). Turned out it was the rev limiter messing with me.

I haven't run into this with a saw yet, but I know they're out there. Not sure how exactly to tune that, except in a cut? Would actually like to hear some advice on that for when I do come across one.

 

[cuinrearview]

You can hear pretty well what I'm talking about in this vid. I had this saw tuned pretty rich. It takes a second in the cut before I pushed on it a little and it cleaned up. WOT=Wide open throttle

 

[cuinrearview]

Don't try and watch to correlate what you're hearing. Just listen.

 

[ADK_XJ]

Yep - follow up to cuinrearview's post, L might need to be touched up again after you get high set. If you ever watched a buckin' billy ray video, you can clearly hear his saws do what he is describing. They sound pretty rough (a.k.a. four stroking) before he starts cutting, but as soon as he puts them to work, they clear up and purr in the cut.

I've found that newer 2 strokes in general with rev limiters are tricky though. You can't do the "lean until smooth and then back rich until burble" thing. I had this with a couple string trimmers I was working on - could not for the life of me get it to tune properly (so I thought). Turned out it was the rev limiter messing with me.

I haven't run into this with a saw yet, but I know they're out there. Not sure how exactly to tune that, except in a cut? Would actually like to hear some advice on that for when I do come across one.

Thanks, does the 440 qualify as a newer 2 stroke?

 

[ADK_XJ]

You can hear pretty well what I'm talking about in this vid. I had this saw tuned pretty rich. It takes a second in the cut before I pushed on it a little and it cleaned up. WOT=Wide open throttle

Nice, that's helpful - I can hear it.

 

[Ryan'smilling]

Thanks, does the 440 qualify as a newer 2 stroke?

A 440 has an unlimited coil, so it's not like what he was describing. A limited coil will only let the engine turn a certain speed, and once the limit is reached, it makes a sound similar to the burble you want to hear, which can be deceiving.

 

[ADK_XJ]

Sharing as much for my own reference as for any future forum members who might be searching around...this video had sort of the walkthrough that I was looking for, although I'm curious what others think of his approach to testing the low and high:

 

[ADK_XJ]

This one is also helpful and seems a little more exact in terms of the approach...my apologies if this is like saw tuning 101 for others, I've never successfully done this before or ever really understood how it works:

 

[trains]

its stock, but it gives you a good idea of the process.

 

[Matt93eg]

A cheap tach is just that. If you want a tool you can trust you'll have to spend some coin. Oh, and you'll want one that goes quite a bit higher than 10k. Some saws rev north of 15k at WOT unloaded.

I agree. OP, if you want a good tach you can't go wrong with a DTI Tech Tach 20k. They are pricey but they work really well with a fast refresh rate. Can be used with the leads hooked up or wireless.

It's best to "develop" your ear to hear the saw and hear the 4 stroking. Not all that long ago I was green to tuning like you. Now I solely tune by ear and sometimes just check with the tach for reference.

The benefit of training your ear is that if the saw leans out due to a problem(air leak etc) you are much more likely to catch it before it's to late. It also makes on the fly adjustments very easy. I always carry a tool in my pocket to tune when I go out and cut.

Another thing with setting the saw to a certain rpm with a tach is if last weekend I set a saw to the no load spec and its 60 degrees, now it's the 30s. It does me no good. You have to recheck it. On the fly adjustments per your ear makes dialing it back in for temp changes very easy without having to get the tach out and piss rev the saw to dial it back in. Also wear ear plugs, I find it helps me hear the burble easier. Here is a link to the tach I referenced.

https://www.amickssuperstore.com/DTI_2_Cycle_Two_Stroke_Hand_Held_Tachometer_p/dti tech-tach tt-20k tach.htm

 

[Ryan'smilling]

Another thing that can help you recognize the burble or "4-stroke" you want to hear is to have someone else run the saw, in and out of wood. Like cutting, and lifting out of the cut briefly at WOT. If you're standing 50' away, it's very noticable.

 

[Evan]

If your worried about tunning before and after a muffler mod, it may be wise to ask someone to tune the saw for you. Might also be wise to not run the saw until help is rounded up

 

[vizette]

If your worried about tunning before and after a muffler mod, it may be wise to ask someone to tune the saw for you. Might also be wise to not run the saw until help is rounded up

I think comments like this, while made with good intention, should have some context or clarity to them...

It's not a bad thing to mess around with your saw(s), that's how you learn. However, you want to be careful that you don't run it lean because you risk damage to the piston and/or cylinder. So if you have someone with experience that can help you, that might be the way to go until you're more comfortable with it.

If not, err on the side of rich if you're unsure. Better to foul a plug or run rough than burn it up. I guess you could argue that you'll carbon up and possibly carbon score if running too rich, but still better than melting the piston.

Side note: I do like Steve's video. Kind of an odd guy, but he usually has good explanations of how and why, and not just "do this".

 

[ADK_XJ]

Sorry, was out busy cutting this weekend - thanks for all the replies, I am going to run to commit to figuring it out for sure over the coming weeks as this is my prime firewood cutting season.

Will report back as I learn.