029/290 muff mod - found the sweetspot

LazyJ · Apr 6, 2008

I proceeded slowly and in multiple steps taking care to test each phase thoroughly with several tanks of gas, kept in good tune, and loaded up in big wood.

First I just reamed out the two existing slots and opened up around the deflector shield exit a good bit, this did very little for performance and the exhaust note hardly changed.

Next I drilled a 5/16" hole in the indented area of the muffler directly inline with the exhaust port which bypasses the internal baffle, surprisingly the increase in throttle response was obvious, running good, sound still well under my Db tolerance.

Today I took a rat file to the 5/16 hole and made it into a slot. Outstanding throttle response, pulls chain alot faster under load, sounds cool with a good "pop-pop" at idle and a tolerable Db at WOT.

I ran two tanks today with a goofy grin on. It sounds and runs so different I decided to pull the plug to make sure I had the carb dialed in right. There's more tan than what this pic shows but it's still whiter than I've ever seen it.

Threw a new NGK in it and opened the H screw just a sniggle, cleaned her up and took pics

Here you can kinda see the increased size of the exhaust exit

Good-looking 10 year old boat anchor

Ray Bennett · Apr 6, 2008

good job.

stihl 440 · Apr 6, 2008

029

Ray Bennett said:
good job.

+1:greenchainsaw:

RiverRat2 · Apr 6, 2008

Ray Bennett said:
good job.

+ 2!!!!!! Yep Repped him good!!!!!

NPKenny · Apr 7, 2008

In my only experience with a 290, you are just getting there. I opened the entire indented area in the muffler and drilled ~4 small holes in the cover. I also opened up the existing outlet on the cover.

If you dind't put the deflector cover back on, then it should be good. If you did put the deflector cover back on over the holes you drilled, I think you still have a bottleneck.

I had to really open the H screw to keep up with the muffler on that saw. It went from being a very poor saw to being a an impressive tool with just the muffler mod and tuning in the carb.

OilHead · Apr 7, 2008

Open up the recessed area all the way & drill a 1/2 " hole thru the front side angle cover . That small exit after a 90 degree turn is a bottle neck. You will be surprised how much exhaust is comming out the front from 1 foot away.

OilHead · Apr 7, 2008

Yeah open it up some more - 13,000 rpm just dont toast the sucker because its too lean. Swing by a saw shop if you dont have a tach to confirm it. :chainsaw:

windthrown · Apr 7, 2008

I did a similar job on my Ebay spare 290 muffler, except I opened up the slots and drilled several smaller (1/8th inch) holes into the dented section. I also cut the cover baffle at a 45 degree angle and opened up the exit port on that quite a bit, but keeping the exhaust ported at an angle. Not quite full throttle, but I wanted to keep it somewhat quieter than a helicopter taking off. I opened up the H screw about 1/2 turn over factory, and I run it a tad rich. It woke the saw right up. I am leaving the saw here with the ex-GF though, so I will put the factory muffler back on and detune the carb. Then I will probably sell the modified muffler on Ebay.

Divorce is a b1tch...

SectorB · Oct 3, 2008

So I modded the 029 super muffler the way LazyJ has done and I also drilled 3- 1/8" holes in the cover just below the exhaust port so it wouldn't bottle neck the gases. I turned the saws H&L screws counterclockwise to start and tune, but it seems to be running fine. IS this normal?? I haven't removed the limiter caps. I did have to adjust the idle to keep it running but that was it. I will post a vid or pics when I can.

WidowMaker · Oct 5, 2008

Here, if I can do it, is shot or two of my 029 Super. Pretty much same as yours. Really woke my saw up, haven't had a tack on it, adjusted the H jet to about 1 1/4 turn and the L jet to about 5/8 turn Has ran a season, cut about 10 cords of wood. The Piston from the exhasut port still looks like new. A little carbon in the exhaust port for some reason.

superfire · Oct 5, 2008

howy cheeze maker

widowmaker you went ape sheet crazy:jawdrop: lazy looks good for a proby muffler hacker. me i think any stock saw sucks. i wait until warranty goes then i goe nutz. my 260 pro is a skreamer with high speed skrew mod and muffler mod. to bad she finally needz to be rebuilt, she is my favorite saw

:greenchainsaw:

stihlboy · Oct 5, 2008

thank you for this post

this is what i have been looking for for quite a while

WidowMaker · Oct 5, 2008

Some of the wood the above has cut..

WidowMaker · Oct 5, 2008

Added a shot to show how I open up the LH side of the cover for more outlet area.

===

Thought I added this to the above post... sorry

SectorB · Oct 5, 2008

Here is the 5/16" in the muffler

I drilled 3-1/8" holes in the cover

Is this to mild to do have any real gains? Like I said, the H and L were turned all the way counterclockwise and it runs, I just don't know the RPMs. The La was adjusted to make it idle better. I want to do this right, any suggestions?

Thanks

woodyman · Oct 5, 2008

This is the one Gremlin did on the MS310 I no longer own.Same muffler as 029,MS290,he gutted it out and added extra pipe out the side and left the stock exhaust.It out cut my brothers MS361 and sounded sweet too.I brought i

t to local dealer for carb adjustment.

nmurph · Oct 6, 2008

here's what i did on my 310, 4 - 3/16" and 1 - 3/8". i keep thinking of opening it up some more, but i don't want to get too greedy. i know there is a point of diminishing returns, i just don't know where it is with this muffler. my currently mod opens the muffler to about 70% of the exhaust opening, as best as i could measure. it really does make a difference on this saw, and i suspect the 290 and 390's as well. i would like to find a 390 p+c to put on my saw. i think i would be getting close to 5 hp. the difference bw the bf and after of my mod feels like the difference bw way it ran bf the mod and my brother's rancher 55, and it sounds cool. definitely louder, but tolerable.
i bought a can of high temp paint, i just have not taken the time to finish the job.

blsnelling · Oct 6, 2008

Go too far and you may have idle problems.

nmurph · Oct 6, 2008

one thing i have done was to retune it a couple of times after modding it. the first was for a little hesitation coming off of idle, the second was to take away a " wee little bit" of the blubber at the top. it still has plenty of 4 stroke, though. i have it running perfect now. it has not needed more tuning for the last 25 hours, or so.
one thing i think that i have noticed is that it cranks better. this may just be a coincidence, but it will now "hit" on the second pull, and start on the third if it has been run the previous day. if it has been more than that, it will hit on the fourth or fifth, and run on the next pull. this is consistantly two to four pulls sooner. fuel is the same, however i have changed to the Ultra oil.

woodyman · Oct 6, 2008

Looks like you opened it up just right.The stock hole on my MS310 was so small I dont see how it put out the advertised 4.0 HP.A muffler mod on the MS290,MS310,MS390 really wakes them up.I added two extra 3/8s holes to my 026 and adjusted the carb.I took it out yesterday and took down a 13" red oak and Im thinking now I might not see too much use out of my muffler modded 359,that 026 really cuts with a sharp chain(it came with a yellow .325 chain,it look like they were cutting rocks with it,with about 60% left on it and after 30 passes on each cutter with the file and taking down the rackers a bit it rips)a sharp chain makes a big difference. :chainsaw:

Hey Brad do you ever leave your PC?Just kidding,you have been alot of help to me. :clap:

029/290 muff mod - found the sweetspot

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