Another MS180 Muffler and Carb Mod

[blsnelling]

I just got my MS180 that I bought for $150. It has normal scuffs from use, but is the cleanest used saw I've bought. The piston and cylinder look like brand new through the exhaust port.

I fired it up and put the tach on it. 14,700, bone stock!!! That surprised me, to say the least. I immediately yanked the Zama carb and threw on the WT-325A. I made no adjustments. It idled good, a little lower, and had great throttle response. The Walbro only brought it down to 14,400. That little of a difference could be in the LA adjustment which I didn't touch. This carb doesn't richen it up much at all. Maybe that's all it needs. I don't know. I'd love to have a fully adjustable carb.

Later this evening, I'll use the spaghetti method and measure the exhaust port and see where I need to go. The factory muffler is very open inside, so no need to uncrimp it. It's a straight shot to the front of the muffler.

Mine does not have a cover like on Mitymouse's 180. I'll just drill a whole for now and see about getting a cover later. Also, I already have a hole through the handle.

This saw sounds like it's totally leaned out even at 14,400, let alone at 14,700 with the stock Zama carb. There's no burble to it at all. However, when I pull the plug, it's pretty dark. I just don't want to fry a nice little saw that already screams in stock trim.

 

[Mitymouse]

Unfortunately I did not check the max rpm before the new carb and muffler mod. One thing to check might be the air filter. I think the new walbro carb flows better than the zama and the air filters on these saws is pretty restricted. Try a run without the air filter, or at least without the top cover on.

 

[blsnelling]

I measured the venturi on both carbs. The Walbro was actually about .005" smaller. Not enough to matter.

 

[Mitymouse]

After I did my muffler mod I put the tach on and it immediately hit 15100. This was with the cover off. I put the cover back on and it sounded significantly slower. I put the tach back on and it was only 14500. After I thoroughly cleaned the air filter it was back up to 15-15100 again. I did notice that it still revved a little slower with the cover on. Seems like I may have to modify the air filter assembly to get more air.

 

[sawinredneck]

I think the jug needs to come off now, lets see what she'll really do!!!

 

[blsnelling]

In order to get 125% of exhaust area you need to drill a 7/16" hole. Here's the math.

The area of the exhaust port at the cylinder wall is 0.267 sq. in.

0.267 * 125% = 0.334 This is the goal of total muffler openings.

There are 17 holes in the factory muffler with a combined area of 0.186 qu. in. That's only 70% of the exhaust port.

We need to add an additional 0.148. A 7/16" hole = 0.150. That puts us at 126%. Perfect. If you want to go to 150%, the max recommended, drill a 17/32" hole. That'll put you at 153%.

I'm off to drill a 7/16" hole.

 

[blsnelling]

I think the jug needs to come off now, lets see what she'll really do!!!

Stop it!!!!!!!!!!!!!!! Ok, that does it. I'm starting to type in Snellerized font

 

[04ultra]

In order to get 125% of exhaust area you need to drill a 7/16" hole. Here's the math.

The area of the exhaust port at the cylinder wall is 0.267 sq. in.

0.267 * 125% = 0.334 This is the goal of total muffler openings.

There are 17 holes in the factory muffler with a combined area of 0.186 qu. in. That's only 70% of the exhaust port.

We need to add an additional 0.148. A 7/16" hole = 0.150. That puts us at 126%. Perfect. If you want to go to 150%, the max recommended, drill a 17/32" hole. That'll put you at 153%.

I'm off to drill a 7/16" hole.

Mine has two 1/4" holes and all the little ones

 

[sawinredneck]

In order to get 125% of exhaust area you need to drill a 7/16" hole. Here's the math.

The area of the exhaust port at the cylinder wall is 0.267 sq. in.

0.267 * 125% = 0.334 This is the goal of total muffler openings.

There are 17 holes in the factory muffler with a combined area of 0.186 qu. in. That's only 70% of the exhaust port.

We need to add an additional 0.148. A 7/16" hole = 0.150. That puts us at 126%. Perfect. If you want to go to 150%, the max recommended, drill a 17/32" hole. That'll put you at 153%.

I'm off to drill a 7/16" hole.

Mine has two 1/4" holes and all the little ones

But that is only in STOCK form, I think we are beyond that now:monkey:

 

[sawinredneck]

Stop it!!!!!!!!!!!!!!! Ok, that does it. I'm starting to type in Snellerized font

"Have grinder and files, will travel."

 

[scotclayshooter]

Stop it!!!!!!!!!!!!!!! Ok, that does it. I'm starting to type in Snellerized font

It was only a matter of time

 

[blsnelling]

The deed is done. I drilled a 7/16" hole. Before the muffler mod and with the Walbro carb, it was running 14,400, down from 14,700 with the stock Zama carb. The first time I checked it with the muffler modded, it went back up to 14,900. After several more checks it's not going above 14,750-14,800. That's only 50-100 above stock. However, if you did the muffler mod with a stock carb and were to gain 300-400 RPMs, you'd be too lean. The Walbro is just enough richer that it bring's it back down to almost stock RPMs with the muffler mod. Considering everything else is stock, that's probably a good thing. Even though there was only a 50-100 RPM gain, I'd guess that there was a nice little jump in HP if you could measure it. I never cut with it stock, so I won't be able to comment on that. All in all, I'm really liking this little saw. It's nice and light and revs to the moon. It should make a great little limbing saw for all those little <4" limbs you want to knock off a freshly dropped tree.

 

[blsnelling]

I tried removing the air filter and the RPMs dropped back down to 14,500. I replaced the air filter and did a chop at WOT and pulled the plug. I wouldn't want it any leaner. It's still tannish brown, but there's nothing dark about it any more.

 

[04ultra]

The deed is done. I drilled a 7/16" hole. Before the muffler mod and with the Walbro carb, it was running 14,400, down from 14,700 with the stock Zama carb. The first time I checked it with the muffler modded, it went back up to 14,900. After several more checks it's not going above 14,750-14,800. That's only 50-100 above stock. However, if you did the muffler mod with a stock carb and were to gain 300-400 RPMs, you'd be too lean. The Walbro is just enough richer that it bring's it back down to almost stock RPMs with the muffler mod. Considering everything else is stock, that's probably a good thing. Even though there was only a 50-100 RPM gain, I'd guess that there was a nice little jump in HP if you could measure it. I never ran cut with it stock, so I won't be able to comment on that. All in all, I'm really liking this little saw. It's nice and light and revs to the moon. It should make a great little limbing saw for all those little <4" limbs you want to knock off a freshly dropped tree.

There fun........One of mine is running 15,100 stock.....I changed carbs and it came down in RPM's with a light brown plug.....Stock Zama it was white.....


What chain are you running....If it has Picco mini......You can slow it down with 3/8 lp

.

 

[ShoerFast]

Mine has two 1/4" holes and all the little ones

Not counting how 'flow' flows, your real close. two .25" holes will have ( two .250 X .7854 = .3927)

Since more little holes will not flow as smothely as the same area of a bigger hole, I bet it's close to the same as the 7/16" hole? but quieter?

 

[blsnelling]

What chain are you running....If it has Picco mini......You can slow it down with 3/8 lp.

I haven't even looked. What is the best chain to run on this saw?

 

[04ultra]

I haven't even looked. What is the best chain to run on this saw?

I have them set up both ways........3/8lp is what my wife runs on her MS180...

 

[Mitymouse]

I have run both 61pmn and 61pmmc3. They both seemed to cut about the same. I have a loop of 34lp from baileys but have not run it yet.

 

[blsnelling]

Help me out here guys. I've never run anything but .375 and .325 chain. What's this 3/8 Low Profile you're talking about? I don't see it in my Stihl Bar & Chain Catalog. It looks to me like PM is the most agressive. The chain that is on it is Oregon and has 25 stamped on the cutters. My bar is a 3005 803 3909. It's 14", .043, Picco, 50DL. The bar looks to be in good shape.

 

[Lakeside53]

The 180 uses PMN - 3/8 0.043 chain. Same as the pole saws and the 170. Cuts great. Not great at boring.

If you put PM on it, it will cut slower due to the wider kerf.