ported 661 baffle in muffler vs baffle out

[Moparmyway]

Hmmm. Interesting. So you actually have to lean it out to get rid of the popping?
Very odd.

No, the 661 tunes itself, but when it does lean out, the popping subsidies unless partially loaded

also...... when a more restricted muffler is installed, it doesn’t pop at all

The 346 is tuned to 15,500 ...... by all measures its lean enough. Even she does it at partial loads with full throttle. When I have the muffler that was on her in the Ct GTG videos (a normal dual port muffler mod) she doesn’t pop at all

With these mufflers, partial load, full throttle, & proper tune; it’s going to be popping.

Try it yourself, I’m curious to see if pulling the front cover on a Stihl muffler without an inner baffle will cause yours to do the same thing

 

[RI Chevy]

Not sure if I have the expertise to do the testing.
Mason and I did a front muff cover test on my 660. I have bug hole in front on one cover. Tough to adjust the idle. And I bought s new solid front cover. The solid front cover gave the saw slightly better operating mannerisms.
No real loss of cut times.
Only thing I can think of is slightly more heat buildup with solid front cover.
I'm curious if you are better off with 1 BIG muffler outlet or 2 smaller outlets.

 

[MustangMike]

Interesting stuff Kevin. I have long believed that the amount of "ideal" muffler mod is often dependent on the other mods to the saw, and have encountered a lot of backlash from the group that believes "more is always better". I have also heard that location of the outlets is another large factor.

Some of my own "informal" observations:

1) Most fully ported saws benefit from complete removal of any baffles and a generous muffler opening.

2) Some of my un-ported 066/660s have more torque if the baffle is just modified, but not removed (I generally drill a 1/2" hole in it).

3) I opened up the dp cover on an Asian 440 Big Bore and the saw drank fuel worse than a ported 660. I put a standard dp cover on the saw and it had the same power but was much more fuel efficient.

While the power each saw makes with various muffler mods is usually easy to document, things like fuel usage are far more difficult unless the difference is extreme.

I also noticed that one of my Ported Asian 660s that seemed to like the modified baffle when I first built it seemed to run better w/o the baffle after it broke in a bit (and I believe RPMs increased).

 

[RI Chevy]

We just joke with you and give you a hard time Mike, but I think you are right on...
The size of the outlets depend on what was done.

 

[Moparmyway]

Not sure if I have the expertise to do the testing.
I'm curious if you are better off with 1 BIG muffler outlet or 2 smaller outlets.

Expertise to do the testing :
1. Can you remove 4 screws ?
2. Can you tune a carb ?

She had one large one, she now has two, and she’s loving these two

Interesting stuff Kevin. I have long believed that the amount of "ideal" muffler mod is often dependent on the other mods to the saw, and have encountered a lot of backlash from the group that believes "more is always better". I have also heard that location of the outlets is another large factor.

Some of my own "informal" observations:

1) Most fully ported saws benefit from complete removal of any baffles and a generous muffler opening.

2) Some of my un-ported 066/660s have more torque if the baffle is just modified, but not removed (I generally drill a 1/2" hole in it).

3) I opened up the dp cover on an Asian 440 Big Bore and the saw drank fuel worse than a ported 660. I put a standard dp cover on the saw and it had the same power but was much more fuel efficient.

While the power each saw makes with various muffler mods is usually easy to document, things like fuel usage are far more difficult unless the difference is extreme.

I also noticed that one of my Ported Asian 660s that seemed to like the modified baffle when I first built it seemed to run better w/o the baffle after it broke in a bit (and I believe RPMs increased).

Did you re-tune anything with these changes yet ?

Last time we discussed this, you didn’t tune the carb to the changes made. Without re-tuning, making changes to the airflow a saw moves is pointless.

 

[Moparmyway]

We just joke with you and give you a hard time Mike, but I think you are right on...
The size of the outlets depend on what was done.

Then explain my 562 please. 100% stock except for the Kevorized muffler mod

“We joke with Mike” .........
I’ll just speak for myself.
I like Mike, but what he does (or hopefully used to do) to a saw necessitates re-tuning to where the saw wants to be, not where he wants it.

His postings should have all started with the disclaimer that he doesn’t re-tune after he changes something.


I’ll just add that tuning in the wood is the only way, I believe, to do it correctly

 

[RI Chevy]

I can tune a Stihl, but I can't tune a Dolkita. ‍

 

[Moparmyway]

I can tune a Stihl, but I can't tune a Dolkita. ‍

Perfect, do it to one of your Stihls. Let us know your results !

 

[RI Chevy]

They are all MOFOs, and 1 CFB Hybrid. Already all done and ready to roll...

 

[huskyboy]

I can tune a unlimited coil saw, but I can't tune a limited coil saw. ‍

Fixt

 

[Adirondackstihl]

Fuel
Cylinder temperature
Etc

 

[MustangMike]

If the saw 4 strokes out of the wood and cleans up in the wood it is where I want it to be.

My saws have done well enough in competition with similar saws that I don't question my ability to tune a saw. Plus, I've never burned one up. Works for me.

 

[drf256]

Very confusing Kevin.

Increasing load increases heat in the cylinder-that’s why 4 stroking goes away under load.

When a factory sets it cylinder timing, I am quite certain that it’s predicated (at least in part) by the amount of exhaust restriction. I believe that’s part of why we are seeing excellent/optimal timing numbers on some of the newer factory Stihl’s. They seem to be going with more open mufflers and less BD than the cylinders of yesteryear.

Could be overscavenging and igniting unburned charge in the muffler. Too much timing pops more under load for me than at piss rev.

Finally figured out why my 361 was popping. The way it was ported, it needed the factory timing slightly retarded, not advanced.

Why it’s happening on all 3 of your saws is certainly a mystery.

 

[Moparmyway]

Why it’s happening on all 3 of your saws is certainly a mystery.

Why: I think enough oxygen is getting into the muffler to allow the raw fuel that is wasted in any 2 cycle to combust. A normal muffler has back pressure, keeping the oxygen out. This happens at partial load, mid throttle and up. Partial load has lots more raw fuel getting out and less load is less fuel needed. A perfect storm, if you will ?

 

[drf256]

2nd port creating a loop of fresh air into muff by venturi effect? Like a header?

 

[RI Chevy]

Wow. Weird...[emoji106]

 

[Moparmyway]

2nd port creating a loop of fresh air into muff by venturi effect? Like a header?

This is why Jeff needs to pull the cover on one of his saws .............. to check out these hypothesis

 

[RI Chevy]

I pull the covers all the time to clean Kevin. But I'm just not a good saw mechanic.
That's why I buy my saws all built.
I'm just not sure what you want me to look at. Next time we meet up, school me please.

 

[Moparmyway]

Easy peasy Jeff

Steps:
1. Pull 4 muffler bolts
2. Put cover to the side
3. Install lower two bolts
4. Run saw and tune
5. Cut something smaller than normal at 1/2 throttle or more and see if it pops

 

[RI Chevy]

I will need in ear plugs and ear muffs. LOL
I've done that before. I hear crackles, but no popping.

I had asked a question earlier if a saw would run better with 1 big exhaust port or 2. The 1 big port may help prevent the "venturi effect. "