MS 290 Muffler Mod

[jteneyck]

I decided to do a muffler mod on my MS290 just to see if it really makes a differenece.  I followed the design of a guy who posted his work on another site since it was about the easiest thing to do, didn't bypass the internal muffler baffles, and didn't require cutting the muffler apart.  Here's a link:   

http://www.arboristsite.com/showthread.php?t=121779&highlight=ms290+muffler+mod

Just taking the cap off the muffler was quite revealing.   The exhaust had to pass through two little slots about 1/8 x 1/4" long.  It's surprising the saw cut as well as it did.  It didn't take long to cut the opening larger, as shown in the pictures on the link.  Actually, it took a lot longer to clean out all the filings, etc. afterwards.  I also was surprised there was no gasket between the muffler and cylinder.  Anyway, I put it back together and went out to give it a try.  I immediately noticed that the saw was running leaner, so it definitely was pumping more air.  I opened up the Hi speed jet until it started to 4-cycle and put it into a 12" ash log.  Definitely cuts better now with much better pulling power when it's fully loaded.  Now I need to replace the chain they put on this saw, RMC3 I think, with something more agressive and it should be a good firewood saw. 

John

[Cut4fun]

I enlarged the 2 existing holes, made 3 others on the outside area and then put one nice biggun  right in the center to by pass the baffle. I ended up with 21% or 23% quicker cut times after carb adjustments on a MS290.


You past up the good info by Brian TW.  (((((You still have the internal restriction from the basket though. IMHO it is better to cut the extra outlet in the dimple, that way the basket gets bypassed.)))))))))

[jteneyck]

I didn't see the info. you referenced, and couldn't find it even after I went back to look but, in any case, I purposefully did not want to bypass the internal basket.  I didn't want the saw to be so loud that I'd be concerned about the neighbors complaining, and I wanted the saw to look stock to the casual observer in case I want to sell it.  The area of the holes in the basket look to exceed the outlet port area by quite a bit, so I figured the greatest restriction was downstream of that.  I'm sure I would get more performance if I open it up more, with a hole in the dimple probably yielding the greatest gain.  I would think my open area is still only around 50% of the outlet port.  But I'll save that for the future if I decide to keep the saw and I forget about what the neighbors think.  So far I'm pleased with the improvement, and I'll run it for awhile to see if it holds true in everyday use.  My wood cutting neighbor said the saw sounds mean now.  Thanks for the feedback. 

John 

[Cut4fun]

Right here 

http://www.arboristsite.com/showpost.php?p=1959827&postcount=7



The one I did was quite and was for my 70 year old father with tender ears to noise. He prefers stock sounding quite mufflers and  he couldnt tell much difference in the sound. The saw looked just like stock, everything done was under the deflector with stock spark screen still in place.

Anything is better then the 2 very small slits they put in there from the factory.

[jteneyck]

Hey, Cut4Fun, thanks for the further clarification.  Now I understand, and might put a hole in the dimple if I want more open area.  But did you leave the deflector unaltered?  It's pretty small in area and seems like it would negate much of the benefit of opening up the stuff inside unless it was opened as well. 

John

[Cut4fun]

I didnt for dad's to try and hold down any noise (just in case it did get to loud) and I still gained 21%-23%. If it was mine I would have opened it up also.

Yes opening the deflector up as you did is the way to go.  


I lied I used 2 holes in center instead of 1. I went back and looked at my MS290 muffler mod thread on www.racesaws.com

[jteneyck]

Well I cut about 5 - 6 face cords of cherry and walnut last weekend, most of it around 12" diameter but some up to 16".  I had to lean the saw up just a bit more, but it was still 4-cycling when out of the wood.  That thing can cut now !  It'll be interesting to do a side-by-side comparison to the newly rebuilt Husky 55 once I get a little run time on it.