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Opening up a muffler on a new chainsaw

Russ

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Rob

03-10-2003 08:42:06




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Further to my other notes, I ended up buying a Husky 353. Seems to be pretty rugged and lightweight. I chose it over the 346xp as Russ you were saying its much the same saw. The 346 turns a lot faster with the special porting in the head but I think the 353 will last better for my limited needs. Russ, I saw a note you put on another board about "opening up the muffler" to get better performance. Can you or someone else tell me what you mean? I presume this means to somehow modify the spark arrestor? I believe in protecting the environment and wouldn't want to modify something that will make it worse but I'd like the top performance you are speaking of.

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jokers

03-11-2003 16:50:29




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 Re: Opening up a muffler on a new chainsaw - Russ in reply to Rob, 03-10-2003 08:42:06  
Hi Rob, sorry it took so long for me to see your post and reply. I`m glad though because I got some interesting reading from the other posts. Here`s the deal, because two stroke engines by their design are known to blow up to 30% of their fuel out the muffler unburned, the tree huggers and then the EPA choose to make an issue of two stroke emissions. I think if you were to compare the quantity and prevalence of all applications of two stroke engines and the gross amount of pollution caused by them, that chainsaws would not be significant contributors, but they do cut trees. So to give the EPA the benefit of the doubt and not say that they pander to the extreme enviromentalists, they have mandated cleaner exhaust emissions from chainsaws. The manufacturers who are either unable to develop cleaner running models due to cost or are unwilling to for whatever reason have chosen instead to make the mufflers more restrictive. Keeping the unburned gases in the hot muffler longer causes some delayed burning of the fuel mixture and accordingly lowers emissions. I`m all for keeping the spark arrestor screen in at all times and favor modifications that retain the screen vs those which just have a couple of pipes out the front, or side, or whatever. In the typical chainsaw muffler there is virtually no tuning involved from the manufacturer but one note of caution, if you make the total outlet size too big, the engine will become "pipey" meaning that it will have a very narrow powerband so it is better to start off with an opening that is probably smaller than what the final size will be. The technique is to end up with a total free open area of 125% to 150% of the exhaust port in the cylinder and don`t forget to include the area of the original opening in this total. You also port match the gasket to ensure that it is not an impediment to exhaust flow. Some saws are more sensitive than others to this mod but all should have the carb adjusted afterward to ensure that you don`t run lean which causes siezures. An opened up muffler will cause your saw to run cooler which will increase it`s life and will also add about 1/2 horsepower to the average saw. Muffler mods offer the most bang for the buck in the typical modified saw, especially if you do it yourself. All modern saws that I`m aware of come with some sort of limiters on the adjustment screws. These can be easily removed if the adjustment can`t be made within the range they provide and then they should be reinstalled. If you take your saw to a dealer without them installed the dealer is obligated by law to replace them and they will charge you for this service. I just picked up a 353 and haven`t done the mod yet, just been thinking on it, but the final design will be a milled slot running diagonaly through the mounting bracket, this way I can sandwhich a screen between the bracket and the muffler which keeps your saw legal for Forestry Service purposes. When selecting a screen make sure that you don`t get one with too small openings or it will negate a significant portion of the benefit you got by modifying the muffler. I know one guy who swears by the screen from stainless steel sieves like you would use in the kitchen but there are many choices if you look around. If you are interested in seeing pics of muffler mods go to the chainsaw forum at arboristsite and do a search for "muffler mods". I`ll try and post a link. Feel free to email me. Russ

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Nolan

03-12-2003 03:35:02




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 Re: Re: Opening up a muffler on a new chainsaw - Russ in reply to jokers, 03-11-2003 16:50:29  
Well written Russ.

Thought I'd give you a little EPA type info, seing as how I work for a state version and am in charge of an air toxics program. :)

The EPA never targeted chain saws. For as you correctly point out, chain saws are by and large an insignificant source.

The EPA did target 2 strokes, et all. Because when you look at the chain saws, weed wackers, leaf blowers, outboard motors, dirt bikes, atv's, mowers, etc, you end up with quite a bit of pollution. Modern 4 stroke engines in cars run very clean, but the 2 strokes are very much not clean burning. Put all those 2 strokes together, and you do get a fair bit of pollution.

The EPA (via Congress)put together standards for 2 stroke engines, and gave the manufacturers years to comply with them. The standards are tiered depending on engine size. You can put more controls on a 60hp 4 cylinder outboard then you can on a little 25cc chain saw engine.

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Jokers

03-11-2003 17:02:03




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 Re: Re: Opening up a muffler on a new chainsaw - Russ in reply to jokers, 03-11-2003 16:50:29  
BTW, I wanted to mention that if your saw is routinely fouling the spark screen at 50:1 you are running with the hi speed screw too far out, ie; too rich. Better to be a little too rich than a little too lean but idealy why not be spot on? You`ll get max power, lower emissions, and increased fuel economy. I run everything at 40:1 and have no problems with any sort of fouling. Oh yeah, remember to run the saw wide open also, no half throttle because they aren`t designed to be run at half throttle. Russ

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Bret

03-11-2003 05:21:13




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 Re: Opening up a muffler on a new chainsaw - Russ in reply to Rob, 03-10-2003 08:42:06  
Husky has a screen type spark arrester on the front cover plate of the muffler. Even at 50:1 mix it WILL clog with carbon/oil. You can either take it off or clean it every few hours. The saw will not run with a clogged screen as there is no where for the exhaust to escape. If you really want to help the "enviroment", then let it clog up. Saw no run, saw no produce smoke/oil/use gas. No flame intended and I understand what you mean, but I tire of hearing about protecting the "enviroment" from people, not you in particular, who rave about "protecting" the enviroment while riding/using their saw/jetski/snowmobile/lawn tractor/Licoln/Ford/Toyota/air conditioning etc.,etc. Somehow it all seems hypocritical to me. I don't dump poison on my fields, but I don't worry about a little exhaust when one volcano or major forest fire puts more crap in the air than man has produced in 100 years. Again, no flame intended, just ranting directed at those elitists who tell us plain folk what to think.

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Rob

03-11-2003 06:24:32




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 Re: Re: Opening up a muffler on a new chainsaw - Russ in reply to Bret, 03-11-2003 05:21:13  
I read what everyone has to say and I learned a lot. What I will do is clean the spark arrestor every morning. I mostly cut in the winter and late fall but I will just get used to using the machine as it is designed. I'll do the same with my Jonsered. But over to the environemental thing Russ, I agree with what you say about the hypocrisy. I just think we've got to start somewhere. I was raised in the summer on an island in the 50's and 60's. We hung a tin cup on a nail on the inside of the boat and when we were thirsty we just dunked it in the lake and drank. And now kids will never know what that is like. I am partly responsible for that and I want to do what little bits I can. I know we all have a say and yes I drive around in a big pickup alone a lot but I try where I can to do my little bit and I know it all makes a difference. I read the other day that every day we use enough saranwrap to cover the state of Texas. I hate that thought and try to use up old plastic bags instead. Only my two cents but there it is.

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Robert in W. Mi

03-11-2003 11:37:38




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 Re: Re: Re: Opening up a muffler on a new chainsaw - Russ in reply to Rob, 03-11-2003 06:24:32  
Good for you Rob, Just because a vulcano or fire pollutes, doesn't mean we shouldn't try to do our own part to help out our own world a little. I plant trees, yes i cut and use trees too, but i'll never saw down as many as i plant. There's nothing wrong with doing a little conservation when we can. Robert



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WRW

03-11-2003 10:42:15




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 Re: Re: Re: Opening up a muffler on a new chainsaw - Russ in reply to Rob, 03-11-2003 06:24:32  
Rob, Using the recommended 50:1 fuel mix ratio you shouldn't have to clean the screen more than once a season. Just take it out and hold a propane torch to it till all the carbon is burned off.
The air filter is another story. It should probably be cleaned each morning despite the manufacturer's claims.
If you grew up in the 50's you probably remember being told not to make snow cream because of nuclear testing.

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F14

03-11-2003 05:49:45




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 Re: Re: Opening up a muffler on a new chainsaw - Russ in reply to Bret, 03-11-2003 05:21:13  
I understand your position. Perhaps it would help a little if I explained mine more clearly.

I'm a firefighter. I live in a rural, heavily wooded area of Maine. I've done my time fighting wildland fires. I don't like it.

I'm familiar with spark arrester screens clogging up. I use quality oil in the proper mix, and I clean my screen when it needs it. I will NOT run a saw without a spark arrester.

If you're cutting in the winter, zipper-deep in snow, that's one thing. If you're cutting any other time of year, the chance of a grass or wildland fire is not worth the risk, especially when it can be prevented by taking care of your equipment properly.

Just my 2�, and it's a free country, so you do what works for you.

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Brian G. NY

03-11-2003 05:30:53




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 Re: Re: Opening up a muffler on a new chainsaw - Russ in reply to Bret, 03-11-2003 05:21:13  
I bought a $99 "disposable" little Homelite 3 years ago and after only a short time it lost it's power. I pulled out the plugged up screen from in front of the muffler and Bingo, full power restored. I've cut a lot of cords of firewood since then without any problems whatsoever.



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Ludwig

03-11-2003 05:40:49




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 Re: Re: Re: Opening up a muffler on a new chainsaw - Russ in reply to Brian G. NY, 03-11-2003 05:30:53  
Don't cut when its crispy dry then...
I worked once with some professional cutters on a landfill job and the first day on the job they all sat on the back of the truck putting the screens back in. I asked why and they pointed to the stacks putting off methane. They'd had a crew member send a spark too close to one of the stacks and WOOOSHH!! Flamethrower.
I had never seen it before but paid attention the next time I saw a chainsaw and sometimes when cutting hard and the screen is removed they throw these little sparks that are kind of hard to see.
The pros also told me thats when its very dry they use the screens too, clean 'em before every work day...

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F14

03-10-2003 12:08:24




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 Re: Opening up a muffler on a new chainsaw - Russ in reply to Rob, 03-10-2003 08:42:06  
I would MOST STRONGLY recommend against fooling with the muffler/spark arrestor on ANY two-stroke engine.

Two-strokes are port-tuned, and changing the backpressure COULD severely screw up the mixture leading to a siezed engine, and will CERTAINLY screw up the port timing. Performance will almost certainly be degraded rather than improved.

The reasons for not defeating the spark arrester should be obvious.

Some folks don't seem to be able to get by the 16-year-old's notion that More Noise = More Power.

My advice is to leave it alone.

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WRW

03-11-2003 05:50:06




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 Re: Re: Opening up a muffler on a new chainsaw - Russ in reply to F14, 03-10-2003 12:08:24  
I run a small consumer grade chainsaw. I have never messed with the muffler, other than to burn the carbon off the screen, and probably never will. I would like to know how changing the backpressure in the muffler can alter the port timing, since that is a function of port size and configuration and it's relation to the piston travel in degrees relative to the crank.
The only tuned exhaust for two strokes that I am aware of are those long pipes with the varying diameters that use pressure waves to push unburned fuel from the exhaust back into the cylinder.

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DaveCA

03-11-2003 06:16:36




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 Re: Re: Re: Opening up a muffler on a new chainsaw - Russ in reply to WRW, 03-11-2003 05:50:06  
At the speed that this all occurs there are pressure waves, or there wouldn't be any noise, right?
The back pressure and pressure wave timing can vary in a short muffler depending on it's particuler features.



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F14

03-11-2003 06:05:59




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 Re: Re: Re: Opening up a muffler on a new chainsaw - Russ in reply to WRW, 03-11-2003 05:50:06  
You are correct, I mis-spoke myself. Obviously "port timing", as you correctly stated, is a fixed mechanical function.

I was trying to point out that altering the muffler could alter the way fuel moves through the system. I may be wrong on that too, but I know from messing with 2 stroke bikes years ago that screwing around with the exhaust without really knowing what you were doing was a good way to screw up a good running bike.

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WRW

03-11-2003 06:52:45




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 Re: Re: Re: Re: Opening up a muffler on a new chainsaw - Russ in reply to F14, 03-11-2003 06:05:59  
The key is "not knowing what you're doing" and yes, even "losing" the screen can alter the fuel/air ratio. It'd be a shame to burn up a good professional grade saw or a wooded area.



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Kevin

03-10-2003 19:53:04




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 Re: Re: Opening up a muffler on a new chainsaw - Russ in reply to F14, 03-10-2003 12:08:24  
I will second that the airflow is tuned. I watched a friend goofing with the carb adjustments on his with no air cleaner. I warned him not to rev it so much without it on, but being smarter than me, 10 minutes of goofing later, kablooey!



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Larry

03-11-2003 13:19:58




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 Re: Re: Re: Opening up a muffler on a new chainsaw - Russ in reply to Kevin, 03-10-2003 19:53:04  
Well I gotta say I'v learn't alot about chainsaws
and what not to fool with.
Thank you all very much.



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