Stihl 4-Mix - FS110 Carboned Up?

[SteveSr]

Hello,

Yea, its not a saw but it cuts and uses mixed gas... Close enough.

This brushcutter from one of our trail crew was turned in to us with the complaint that it would start but wouldn't run. Here are the findings so far:

• Muffler screen was completely clogged except for a small round patch near the outlet.
• Spark plug was black.

Here is what has been done so far:

• Spark plug changed - No improvement
• Spark screen cleaned with a torch - No improvement
• Gas dumped and replaced with fresh - No improvement
• Run without air filter - No improvement
• Fuel filter and lines checked - No issues found
• Carb swapped with an OEM replacement - No improvement

Based on the initial examination it would appear that something is still choking this engine out. Before I tear it apart further are there any passages in the muffler that could still be clogged? Unfortunately it is a sealed can. Any other suggestions?

Thanks,
Steve

 

[frank_]

valve clearance/rocker adjustment maybe ?

 

[Woodslasher]

Hello,

Yea, its not a saw but it cuts and uses mixed gas... Close enough.

This brushcutter from one of our trail crew was turned in to us with the complaint that it would start but wouldn't run. Here are the findings so far:

• Muffler screen was completely clogged except for a small round patch near the outlet.
• Spark plug was black.

Here is what has been done so far:

• Spark plug changed - No improvement
• Spark screen cleaned with a torch - No improvement
• Gas dumped and replaced with fresh - No improvement
• Run without air filter - No improvement
• Fuel filter and lines checked - No issues found
• Carb swapped with an OEM replacement - No improvement

Based on the initial examination it would appear that something is still choking this engine out. Before I tear it apart further are there any passages in the muffler that could still be clogged? Unfortunately it is a sealed can. Any other suggestions?

Thanks,
Steve

I'm not familiar with a 110, but yes the muffler can be clogged. I was sitting in the house listening to my younger brother run the weedeater and I noticed it sounded "off". Long story short the spark screen was plugged as well as the muffler, which was a bear to clean. Based off of pics I saw on the internet, I'd suggest you gut the muffler. I recently gutted the cat-equipped muffler on a Husky 235 and the process should be similar on your muffler. What I did was I used a drill to drill out a slot in the strip of the back half of the muffler that is crimped over the front. Then I just took a screwdriver, pried up all the crimped material and popped the front cover off. The cat got chucked, I opened up the outlet a little more, then I just used a hammer to re-crimp the muffler halves together.

 

[SteveSr]

valve clearance/rocker adjustment maybe ?

Will check this but this is not a high use / high hour machine. Probably slightly more than a typical homeowner machine.

 

[Lee192233]

valve clearance/rocker adjustment maybe ?

+1 on the valve clearance. I have a KM110. I was amazed how far out the valve adjustment was when I checked this spring. I probably have about 15-16 tanks through it in 9 years. I believe the spec is .004"(0.1 mm).

 

[SteveSr]

I'm not familiar with a 110, but yes the muffler can be clogged. I was sitting in the house listening to my younger brother run the weedeater and I noticed it sounded "off". Long story short the spark screen was plugged as well as the muffler, which was a bear to clean. Based off of pics I saw on the internet, I'd suggest you gut the muffler. I recently gutted the cat-equipped muffler on a Husky 235 and the process should be similar on your muffler. What I did was I used a drill to drill out a slot in the strip of the back half of the muffler that is crimped over the front. Then I just took a screwdriver, pried up all the crimped material and popped the front cover off. The cat got chucked, I opened up the outlet a little more, then I just used a hammer to re-crimp the muffler halves together.

Since this is a 4-mix and not a regular 2-stroke I don't believe this is a CAT muffler. There are also no extra heat shields that would indicate a CAT. Can anyone confirm this? I seem to recall that avoiding emissions and the need for a CAT was one of the reasons for making these a mix lubed 4-stroke engine.

 

[cscltd]

No cat, try running with muffler loose to see if runs better and tighten and loosen on the fly to see if big difference. And check metering diaphragm to see if stiff

 

[SteveSr]

No cat, try running with muffler loose to see if runs better and tighten and loosen on the fly to see if big difference.

Will do.

And check metering diaphragm to see if stiff.

I suspect that this started as an old fuel / carb issue. Now the question is how to get rid of the carbon build up.

 

[HarleyT]

Here is a bulletin you might read.

 

[HarleyT]

Here is the manual.

 

[HarleyT]

Running without the debris-shield {long cutting swath} will cause carbon problems also.

 

[cookies]

I have seen people complaining about these 4 mix tools having valve adjustment problems and scored cylinders with low or very low hours.

 

[SteveSr]

Here is a bulletin you might read.

Thanks. The instructions say that this is mainly for ash deposits which I would expect to be dry. However, this engine appears to be fouled with unburned oily deposits. I also found the MSDS (attached) for this product which lists it as 85-90% water. Because of this I am wondering how this will work on these oily deposits. Anyone have any real world experience with this product and oily deposits?

 

[SteveSr]

Here is the manual.

Got it. Thanks!

 

[SteveSr]

Running without the debris-shield {long cutting swath} will cause carbon problems also.

Yea, this is just a BAD idea. It severely overloads the powerhead... Like continuously bogging a chainsaw. It is a red flag for me when looking for used equipment and see that the shield has been removed.

This particular trimmer may have had the opposite issue. It has a polycut (nylon blade) head which is much more aerodynamic than string line so the engine may spend a significant amount of time bouncing off of the rev limiter which can't be good for combustion efficiency.

 

[frank_]

the airflow through the carb is affected by the crankcase pressure on these too
i tried to run one with the rocker cover off and is refuse to run ( i even spun it with a drill)
but it fired up first pull when the rocker cover was refitted
so a leaking gasket might affect it bogging

 

[HarleyT]

Thanks. The instructions say that this is mainly for ash deposits which I would expect to be dry. However, this engine appears to be fouled with unburned oily deposits. I also found the MSDS (attached) for this product which lists it as 85-90% water. Because of this I am wondering how this will work on these oily deposits. Anyone have any real world experience with this product and oily deposits?

Here in redneck country, one way to break up carbon deposits in an engine is to dribble water into the intake while the engine is running, it breaks up the carbon {supposedly}.

 

[furb]

Here in redneck country, one way to break up carbon deposits in an engine is to dribble water into the intake while the engine is running, it breaks up the carbon {supposedly}.

I know someone that said the water worked in a 5.7 vortec. I’ve never tried it.

 

[cscltd]

I have seen people complaining about these 4 mix tools having valve adjustment problems and scored cylinders with low or very low hours.

Only Echo dealers/fans say that-lol
first version yes problems, later versions, not really

 

[SteveSr]

Here in redneck country, one way to break up carbon deposits in an engine is to dribble water into the intake while the engine is running, it breaks up the carbon {supposedly}.

Yes, this is an old trick and it does work, at least on car engines. The water vapor flashes into steam during combustion and breaks the carbon up and sends it out the exhaust. With the Stihl de-carbonizer you are supposed to dump it out of the engine before starting it but there will obviously be some remaining.