Stihl MS 170 bogging down, no power
- Thread starter GerrySM
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sugarbush
ArboristSite Guru
don't know why someone with your chainsaw expertise bothers asking for help.
GerrySM
ArboristSite Operative
Guys, I have not found that an adjustable carb makes that much of a difference on a 2-stroke engine. I had my carbs on my bigger saws professionally adjusted by 2 different small engine workshops, and their mufflers still got dirty.
Please note that since I have lost power on my machine, it's actually been burning white (lean). The inside of the muffler is grey and clean, and the spark plug looks very clean (too clean). This just supports my theory that the loose bolt on the carb mounting was allowing air in. An adjustable carb will not fix this.
Please note that since I have lost power on my machine, it's actually been burning white (lean). The inside of the muffler is grey and clean, and the spark plug looks very clean (too clean). This just supports my theory that the loose bolt on the carb mounting was allowing air in. An adjustable carb will not fix this.
Chris-PA
Where the Wild Things Are
It's possible that the bolt was loose enough to cause it, but you will find that out.
Really though keeping the muffler spotless is not the goal of tuning - keeping the engine healthy and producing good power is. There is no real hope of keeping the muffler clean with a fuel system than goes so rich it misfires with only a slight lift and rpm increase.
abikerboy
ArboristSite Operative
Keep in mind also that they do make different jets for these carbs. I know there is a high altitude jet and a low altitude jet. Don't know if they're others or not. My dealer and I were talking about these carbs a while back, and that's how I learned about the jets. When the saw leaves the factory, they jet it for whatever part of the country that it will be sold in. When you get your new carb, and especially with it coming from another country, you may have to buy a different jet for it. That is the only way to adjust these carbs, and that only changes the high side. You're pretty much stuck with whatever you get on the low side. When the time comes for carburetor service on my MS170, I'm going to put an adjustable one on it and call it a done deal. Not worried about it right now though as it runs pretty good with the stock one.
GerrySM
ArboristSite Operative
Ah well, for a few dollars extra I should have bought the adjustable, but too late now.
abikerboy
ArboristSite Operative
Don't get too worried yet, as there may be a pretty good chance that it will work right off the bat. And even if you do have to rejet, those jets shouldn't cost too much.
Chris-PA
Where the Wild Things Are
I'd be extremely skeptical about this claim from your dealer. These are the very cheapest of mass produced saws, and I doubt they have any idea where they are going when they are built. If the carbs are jetted differently then they would have different part numbers, so someone who knows Stihl can easily verify it.
abikerboy
ArboristSite Operative
I'm really not sure if that is so, or not. I haven't had any carb problems with mine, so I don't even know if the jet is removable. It just came up in conversation with him. I would really like to know if that is true.
Edit: The ipl does show fixed jet 0.45 part#1130-121-5604 and high altitude fixed jet 0.42 part#4137-121-5601
GerrySM
ArboristSite Operative
I bought a Harbor Freight style sand blaster today (from the Australian store supercheapauto.com.au on a special) and used it on the muffler, using only sodium bicarbonate. Wow! Looks brand new. I will spray it silver and post pics in a few days. Meanwhile, I can highly recommend one of these units to y'all. It just revolutionises cleaning and rust removal.
GerrySM
ArboristSite Operative
I remember looking into this years ago, and the info I got then is that most saws, Huskies specifically, are jetted/adjusted from factory for sea level. I'm at 450m (1500ft) and that is still considered low altitude (only just), so no re-jetting required (although it would be nice if I could run a little bit leaner, I admit). That's probably why I am seeing a little carbon building up, when it is running normally. Could I fix this by going from 50:1 to 60:1, or 70:1? Or are carb settings and fuel mixtures different creatures entirely?
I think you have to get up over 600m/1800ft to justify re-jetting these units, from memory (could be wrong, will check if you push me)
If you run at close to the same temperature all year you could get by with a non adjustable carb, over here when I have a carb adjusted right for the winter -5 to 15 above F the saw will be pig rich when it gets up to 80 F. Steve
GerrySM
ArboristSite Operative
Is there supposed to be a gasket between the muffler and the body on the MS170? Mine does not have one and the dealer says it does not come with one .... all my other saws have had one.
Can't find the relevant parts diagram.
Can't find the relevant parts diagram.
VinceGU05
PSA vitim.
nope .. doesnt have one.
GerrySM
ArboristSite Operative
New Chinese carb made no difference, in fact it ran worse. I had to wind back the idle speed to the lowest setting and still the chain was advancing. They'd sold me a carb using a listing that had a picture of a Zama carb, but when I got it I found it was a generic carb, a lookalike 
, so I started a claim on eBay and got the money refunded.
Then I made the belated but fortunate discovery that the saw was on the last day of its 2 year domestic use warranty, so I rushed it in to the dealer (d'oh!)
Dealer found that the seals on the original carb had deteriorated allowing air in and making it run too lean. I did not quite understand the explanation over the phone, will speak to them more when I pick it up. It's not the gasket he's talking about, but some sort of seal on a hole/s drilled in the carb by the manufacturer for some sort of reason. Maybe he's talking about a diaphragm? They also replaced the tiny brass jet I broke and then lost.
They tell me it's running great now.
No charge. Phew!
, so I started a claim on eBay and got the money refunded. Then I made the belated but fortunate discovery that the saw was on the last day of its 2 year domestic use warranty, so I rushed it in to the dealer (d'oh!)
Dealer found that the seals on the original carb had deteriorated allowing air in and making it run too lean. I did not quite understand the explanation over the phone, will speak to them more when I pick it up. It's not the gasket he's talking about, but some sort of seal on a hole/s drilled in the carb by the manufacturer for some sort of reason. Maybe he's talking about a diaphragm? They also replaced the tiny brass jet I broke and then lost.
They tell me it's running great now.
No charge. Phew!
felt, ftw.
scotchbrite not only wont filter fine stuff, it does come apart. will polish up the piston when it does. just my $.02.
GerrySM
ArboristSite Operative
Ok, final update on the carb saga.
Dealer technician showed me inside a carb exactly what happened. The sealant on the welch plug had deteriorated allowing air to be sucked. The sealant runs around the edge of the welch plug, about 1mm thick, barely visible.
He replaced the plug and sealant, and it runs fine now.
He says a lot of new, cheap chainsaws sold at Bunnings (Australia's Home Depot) have this problem due to sitting in a hot warehouse for a long time. The sealant can go. He has them coming in for this repair frequently, right after they are bought from Bunnings..
This is not a repair a home handyman can do easily. You need a special punch (and a special sealant, and a very tiny applicator) to get a new Welch plug back in.
He did not know why the new Chinese carb did not improve the situation. Moral of the story: don't buy Chinese carbs off eBay.
Dealer technician showed me inside a carb exactly what happened. The sealant on the welch plug had deteriorated allowing air to be sucked. The sealant runs around the edge of the welch plug, about 1mm thick, barely visible.
He replaced the plug and sealant, and it runs fine now.
He says a lot of new, cheap chainsaws sold at Bunnings (Australia's Home Depot) have this problem due to sitting in a hot warehouse for a long time. The sealant can go. He has them coming in for this repair frequently, right after they are bought from Bunnings..
This is not a repair a home handyman can do easily. You need a special punch (and a special sealant, and a very tiny applicator) to get a new Welch plug back in.
He did not know why the new Chinese carb did not improve the situation. Moral of the story: don't buy Chinese carbs off eBay.
This is true. Any saw dust will simply pass through the venturi of the carb. There's nothing to draw them into carb orfices as fuel is coming out of those.
Definitely.
Glad you got it running right. BTW, a welch plug is simple to remove and replace. Drill a small hole in it and remove it with a wood screw. Install it with a flat punch. Sealant should not be required, but nail polish can be used.
Where is the real one from Stihl made. Steve
