Echo chainsaw "bogging" when throttle applied

[arakboss]

My Echo 355t chainsaw has been giving me fits but was nearly unuseable this past weekend. It will start fine and idle ok but it "bogs down" when throttle is applied. After watching some videos on youtube, I think it might be that the muffler (spark arrester) is plugged up. I did notice some wet black gunk around the muffler exhaust port area. Prior performance issues were decreasing lack of power and the saw would frequently die after completing a cut.

Is a plugged muffler the most likely culprit or should I look at another area first? I have not done any maintenance to the engine other than scrape off the air filter. I tried briefly running the saw without the air filter and it still "bogged down". When it bogs down it continues to run but doesn't have enough power to turn the chain.

I have numerous Stihls and an Echo 310 but this top handle 355t has become my favorite saw. It ran like a son of a gun when new and I want that performance back. I don't have any way to check the compression but I don't believe it is anywhere close to being worn out.

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[The Heretic]

Plugged intake (air filter), exhaust, gummed up carb.

 

[baker3gun]

Starting points:

1
Compression checkers are cheap. Look for old ones at garage sales. Usually, any decent checker has common threads that can receive any size adaptor to fit any size spark plug hole.

Usuallyif a power saw has over 100psi compression, it can run pretty good.

Harbor freight store nearby?

2
Maybe you have an air leak due to a failed seal in carb.

3
Maybe you have a blockage in the carb, or maybe the pump diaphragm in the carb has a hole in it.

4
Maybe you have a leak in the fuel hose.

5
Maybe you have a fuel hose blockage. They usually have a filter stabbed on the gas-tank end. Maybe the filter is plugged.

It's not hard to do a carb job on these things. Plenty of online tutorials on youtube or arboristsite.com.
Carb kits usually cost $10. They come with all new gaskets, diaphragms, needle, etc.

Generally, there are two kinds of "engine died when I gave it throttle".
1 - the engine starts to try to rev up but falls abruptly on its face, and it's not very dificult to restart it back to an idle. Usually, that's lean. Not enough gas getting through the Hi jets, or an air leak somewhere that allows the vaccuum pressure to suck air instead of fuel.
2 - the engine starts to rev up but them makes a "bloooah" ("bleah like snoopy?") sound and dies, and is kind of difficult to restart. Usually that's rich, too much gas or not enough air coming in as engine begins to rev.

IMO, the most likely fix based on what you said:
Carb job with carb kit, inspect fuel hose for blockage or leak. Check plug gap, set to spec.
You should probably check compression first.
If it only has 40psi, you need a piston and maybe a cylinder, and your carb might be flawless.

Tip - don't blow high-psi air into little bitty carburetors. Some of them have internal check valves that you can lock up, which will ruin the carb.

Tip 2 - don't be afraid to remove welch plugs from carb if yours have them. You need to look under those things for blockage. Youtube has vids on how to remove and replace.

Good luck! Keep us posted. Ask more questions. Someone here knows the answers.

 

[arakboss]

It looks like getting the spark arrestor screen off is pretty easy and free, so I will give that a try tomorrow. If a plugged screen isn't the problem I will start chasing the other items.

 

[The Heretic]

It looks like getting the spark arrestor screen off is pretty easy and free, so I will give that a try tomorrow. If a plugged screen isn't the problem I will start chasing the other items.

If you can take it off, please put it back on if you can unplug it or replace it.

Equipment without spark arrestors cause fires and we don't need that.

 

[TTSX]

You "scraped off" your air filter......? That sounds really gross

 

[DeanfromOregon]

Once you get it all cleaned out, check your fuel mix ratio. Sounds like you may be a little rich.

 

[Hop Sing]

FWIW, I had that problem on my Echo saw and fixed it by installing a new gas feed line to the carb. Lots of tutorials on that on you tube.

 

[arakboss]

You "scraped off" your air filter......? That sounds really gross

The air filter gets caked with sawdust occasionally. That sawdust is wet with a combo of tree sap and b&c oil so it just shake off. The filter is due for replacement but I ran the saw with out the filter and saw no improvement in "bog".

 

[arakboss]

FWIW, I had that problem on my Echo saw and fixed it by installing a new gas feed line to the carb. Lots of tutorials on that on you tube.

I will add that to list of items to check. There is a filter on gas intake line I will replace first before replacing the whole line.

 

[arakboss]

If you can take it off, please put it back on if you can unplug it or replace it.

Equipment without spark arrestors cause fires and we don't need that.

I am very conscious of fires and will attempt to clean spark arrestor before replacing it. We had three wildfires in the area this weekend.

I am careful with mix ratio but I am running the saw at 5000+ feet of elevation, that may result in the rich fuel mixture. The manual states that the saw is tuned for up to 1100ft of ele. It states that you have to have a dealer do adjustments for higher elevations, probably because of limiter caps on mixture screws (epa emissions?)

 

[albin25]

Have you tried running it with the fuel fill cap loosened?
It's not uncommon for the tank/cap vent to get restricted/plugged preventing the tiny fuel pump from pulling adequate fuel. At least that was the problem on my hedge trimmer.

 

[arakboss]

Have you tried running it with the fuel fill cap loosened?
It's not uncommon for the tank/cap vent to get restricted/plugged preventing the tiny fuel pump from pulling adequate fuel. At least that was the problem on my hedge trimmer.

I haven't but I will try that, thanks for the tip. It does collect sawdust around the cap but I didn't about a vent hole in the cap.

 

[baker3gun]

The purpose of limiter caps is to prevent end users from turning the Hi screw out enough to make the saw run rich enough that it starts to "4-stroke" at peak rpm.

"4-stroke" is a colloquialism for what happens to a 2-stroke engine when its fuel pump begins to push so much fuel down it's throat that it gets so rich that it can't continue to increase rpms.

It's the sound you hear when a saw goes from a clean climbing howl to a ratty disorderly overfed braaap.
It's definitely not that grainy thing you hear when a lean saw goes from a clean climbing howl to a thin raging scream.
The former is life. The latter is death.

While buried in wood, if your hot saw howls cleanly up to peak rpms and pulls hard but instantly goes ratty braap if you lift the bar slightly while holding full throttle, that ratty sound is known as "4-stroking".
If it goes grainy screaming faster, you are lean and killing the motor.

The way to achieve 4-stroking is to richen the main jet array (turn the Hi screw counterclockwise) enough that a hot saw goes ratty when you lift the load off it at peak rpms. Basically, this is the engine revving to a point where the richness curve associated with the cyclic rate of the carb diaphragm halts the rpm progression ramp. It's an organic rev-limiter if you will.

This setting usually results in optimal power output, nearly always results in longest possible engine life, and farts out 7ppm more undesirable gases than a somewhat leaner engine.

EPA decided that the additional fartgas was way too much, and they instructed the saw manufacturers to put limiter caps on the screws so that end users could not set the saw slightly rich and get peak power and a ratty 4-stroking organic rev-limiter. Instead, the engine would run slightly lean and never see enough fuel to reach the richer peak crossover point where the carb pulls more fuel than the engine can handle.

The manufacturers were like, "Cool man, this will cut engine life in half, so we can sell twice as many saws!"

Real men circumvent the stupidity of EPA and the greed of manufacturers by modifying limiter caps. Just pull em off, cut off the limiter tab, and stick 'em back on. At least that's how it used to be. I have no idea how they are doing it now.

Usually, the idle and Lo screw adjustments are ordinary.
Idle - set it first. Set it so that the chain just stops spinning when you idle.
Lo - set it next. Set it so that the leap from low to high rpms is fat and angry, not starved, and not bleah boggy rich.
Hi - get the saw hot and bury the bar. Tweak your Hi screw until your saw instantly 4-strokes when you lift the bar out of the load but not while it's in the load.

Caution: When tuning the Hi screw, if you go too rich, the saw will just be ratty and disorderly at any high rpm, which is not harmful to the engine. If you go way too lean (too far clockwise), the saw will rage into screaming rpms that burn up the motor.
Better rich than lean. Be careful as you seek a good setting.

It is not unusual for experienced cutters to tweak the Hi screw daily or even several times a day as conditions change: very small changes, made when things don't feel and sound just right.
Not unusual in settings where 50° intraday temperature swings are completely normal. Like today in Baker County. 38 when I got up, 85 at 2PM.

OK then arak op man. Hope this helps. Good luck with your saw.

 

[baker3gun]

Most air filters I've seen are gasoline safe.

Dunk it in a bowl of gasoline and swish it a while and shake it off and air dry it, then try it again.

If you had to scrape off gunk, maybe the media is so plugged with oily grime that the saw can't breathe air and so it bogs rich.

ETA: I see where you said that the saw still ran poorly with filter removed. To cover all bases, it should be noted that if you had a clogged filter causing a rich problem and you removed the filter and still had a problem, consider that a clean filter is an air restriction, and if you remove a dirty one, your saw could go from rich to lean and still have problems, because a saw with no filter will run leaner than a saw with filter.
I'm not saying that's what is happening to you, only pointing out possibilities.

Also, I put a likey on albin and Hop Sing posts because they make good points.

And, I'm not familiar with your saw. I've never had a saw that had a problem with blocked exhaust, but if your saw has that tendency and you clean that arrester and it runs like a champ, that's a homerun. Try it; let us know what you find out.

 

[arakboss]

Most air filters I've seen are gasoline safe.

Dunk it in a bowl of gasoline and swish it a while and shake it off and air dry it, then try it again.

If you had to scrape off gunk, maybe the media is so plugged with oily grime that the saw can't breathe air and so it bogs rich.

ETA: I see where you said that the saw still ran poorly with filter removed. To cover all bases, it should be noted that if you had a clogged filter causing a rich problem and you removed the filter and still had a problem, consider that a clean filter is an air restriction, and if you remove a dirty one, your saw could go from rich to lean and still have problems, because a saw with no filter will run leaner than a saw with filter.
I'm not saying that's what is happening to you, only pointing out possibilities.

Also, I put a likey on albin and Hop Sing posts because they make good points.

And, I'm not familiar with your saw. I've never had a saw that had a problem with blocked exhaust, but if your saw has that tendency and you clean that arrester and it runs like a champ, that's a homerun. Try it; let us know what you find out.

I brought the problem child to work with me and I will tear into on my lunch break. I have compressed air here so I can blow out filters and debris in and around case. I will fire it up tomorrow at home.

 

[arakboss]

I have a high level of confidence that the spark arrestor was the problem. Only about 25% was open to passing exhaust. The rest of the area was plugged with very stubborn carbon. I was able to get it clean but it was a chore. Air filter was cleaned too and spark plug looks good. If it still bogs down I will starting checking the fuel supply. I will report back late morning with results on how it runs.









Inside of chamber and muffler looks pretty gunked up too, that will be a project for another time.

 

[arakboss]

My saw is running like new again. It was definitely the spark arrestor screen causing the problems. This morning, I busted through some left over pieces of logs from the ice storm. It ran like a beast. I now notice how much the performance of the saw has been deteriorating over the years. I could have saved myself a ton of grief if I had made cleaning the spark screen an annual chore.

Hopefully it will work as well once I get up to 5200ft. I am headed back down to cabin this weekend for short stay to do some more wildfire prep at my place and helping out the lady who watches over my place. She is pretty worried about all of these fires they have been having down there.

I will fuss with the carb adjustments once I get there.

Thanks to everyone for the help.

 

[Hop Sing]

Congrats at solving the problem! And thanks to all (especially baker3gun) who posted such valuable information - I am sure it will come in handy some day.

 

[Certaindeaf]

It's probably a crudded up spark arrestor.







lol