Help with tuning MS 661 carbureted model

[Stihldobie]

Hello All,
I have a 2022 MS 661 carbureted model. I recently modded it with a West Coast Saw Bark Box. I have run several gallons of Husky premix. Saw has never seen ethanol. Currently I am at 2.75 turns on the L and 2.25 on the H. Plug is still very white. The limiters are removed so these settings are from needle seat to aforementioned position. Saw seems to run ok, but does fluctuate rpm in the cut. If I go further out on the H, rpm seems to drop off as would be expected. No matter what I do, the plug remains mostly white. Either way, the needle screws don’t seem to respond like I am used to. Anyone have any thoughts on this?

 

[Mad3400]

Assuming the powerhead is in good working order with no issues, just keep turning the High jet "Out" in increments until the plug or exhaust screen turns your desired shade of brown.

A Tachometer is also a worthy investment.


Mad3400

 

[Stihldobie]

Assuming the powerhead is in good working order with no issues, just keep turning the High jet "Out" in increments until the plug or exhaust screen turns your desired shade of brown.

A Tachometer is also a worthy investment.


Mad3400

Assuming the powerhead is in good working order with no issues, just keep turning the High jet "Out" in increments until the plug or exhaust screen turns your desired shade of brown.

A Tachometer is also a worthy investment.


Mad3400

Yes, power head is mint. Low hour saw. Turning out the high jet will richen it up and knock down rpm and performance, but even keeping it rich enough to do this will not make that plug anything but white. And it starts sounding really weak and ratty.

 

[Mad3400]

They aren't like the older saws where you turn them pack 1 to 1 1/2.

I believe in my case, after removing the limiter caps, it was 3 to 3 1/2 turns.

Maybe there's little bits of debris clogging the jets just enough to be a pain?


Mad3400

 

[stihltech]

Stihl shop manual states 1 turn on low side and 1 1/2 turns on high side. You need to look for vacuum/pressure leak. Also check the fuel supply side.. Don't forget the vent. Definitely too lean somewhere.

 

[Stihldobie]

They aren't like the older saws where you turn them pack 1 to 1 1/2.

I believe in my case, after removing the limiter caps, it was 3 to 3 1/2 turns.

Maybe there's little bits of debris clogging the jets just enough to be a pain?


Mad3400

Fairly new saw. Maybe 4 gallons through it. Bark Box went on half way through. Changed plug to get baseline. It seems to burn one side of the plug. Not bad on the one side, but the other is white. It’s strange. Everything I have ever owned has been tuned, up to and including a 1700 hp blown small block. Been around for a long time, but this one has me stumped. If I turn the high out beyond 2.75, the plug doesn’t seem to change, but the rim is wet after an immediate high load shutdown . Don’t want to wash the cylinder walls with a rich condition.

 

[Mad3400]

Fairly new saw. Maybe 4 gallons through it. Bark Box went on half way through. Changed plug to get baseline. It seems to burn one side of the plug. Not bad on the one side, but the other is white. It’s strange. Everything I have ever owned has been tuned, up to and including a 1700 hp blown small block. Been around for a long time, but this one has me stumped. If I turn the high out beyond 2.75, the plug doesn’t seem to change, but the rim is wet after an immediate high load shutdown . Don’t want to wash the cylinder walls with a rich condition.

That's true, don't want to wash the Cylinders.

It is quite puzzling, especially with such low use.


One thought is that they have quite a bit more "Rattle" or vibration once you add a Bark Box or Straight Shot to these.

Also, if you leave them on the ground idling a lot it's a bit more intense.


Could have loosened up the Intake boot or carb bolts just enough to suck air, so try tightening those up a bit.



What size bar are you running?


Mad3400

 

[Stihldobie]

That's true, don't want to wash the Cylinders.

It is quite puzzling, especially with such low use.


One thought is that they have quite a bit more "Rattle" or vibration once you add a Bark Box or Straight Shot to these.

Also, if you leave them on the ground idling a lot it's a bit more intense.


Could have loosened up the Intake boot or carb bolts just enough to suck air, so try tightening those up a bit.



What size bar are you running?


Mad3400

I run a 36” bar on this usually. Pretty careful with not leaving it idling on ground. I run the cut, give it a couple high rev snaps, let idle for 10 secs and shutdown. It definitely doesn’t sound like an air leak. Fires right up, from cold, has a clean idle, and cuts hard. Just hate seeing white on my plug. Starting to wonder if the additional exhaust venting from the bark box is causing issues in the burn with air fuel mix.

 

[Stihldobie]

That's true, don't want to wash the Cylinders.

It is quite puzzling, especially with such low use.


One thought is that they have quite a bit more "Rattle" or vibration once you add a Bark Box or Straight Shot to these.

Also, if you leave them on the ground idling a lot it's a bit more intense.


Could have loosened up the Intake boot or carb bolts just enough to suck air, so try tightening those up a bit.



What size bar are you running?


Mad3400

Here is the plug after a 40” cut through red oak.

 

[Mad3400]

I run a 36” bar on this usually. Pretty careful with not leaving it idling on ground. I run the cut, give it a couple high rev snaps, let idle for 10 secs and shutdown. It definitely doesn’t sound like an air leak. Fires right up, from cold, has a clean idle, and cuts hard. Just hate seeing white on my plug. Starting to wonder if the additional exhaust venting from the bark box is causing issues in the burn with air fuel mix.

Try testing that theory by swapping the Bark Box with the Stock cover and running a couple tanks.


Mad3400

 

[Stihldobie]

Try testing that theory by swapping the Bark Box with the Stock cover and running a couple tanks.


Mad3400

That is my next move. I only hope that WCS has done testing on their mufflers before selling to market. More to follow.