Cleaning carb on smoking Stihl

[coppicer]

I have been using a Stihl MS181 for 6 years now, and for my purposes it's been a good little saw, despite my never really maintained it. I have taken it into the shop for a service once or twice, but it didn't seem to have any effect on operation - was neither better nor worse after the service.

 

Yesterday, when I started and revved the saw with the bar and chain off, it started to get hot and began to smoke from around the sprocket, so I turned it off immediately and let it cool. I thought it might be a problem with the air-fuel mix, and thought I would take the opportunity to service the carb, as the saw sometimes has problems when revving off idle, as described here. I have already replaced the spark plug and air filter, just in case.

 

While taking the saw apart, I have already found a couple of issues, including the fact that two out of the three T27 screws that are supposed to hold the carb on simply aren't there. ? As I have never taken the saw apart, I can only assume the shop failed to put it back together properly after the service, which (if true) is disappointing. I also can't see any sign of the O-ring 9646 945 0610 mentioned on p.72 of the service manual in relation to the stop buffers (why would a stop buffer have an O-ring?).

 

I was planning to replace all the diaphragms and other rubber parts in the carb. I've cleaned bike carbs before, but not chainsaw carbs and I am surprised that the outside of the carb is so filthy with sawdust, etc. How do I clean this? I don't have an ultrasonic cleaner. I have no objection to going at it with a scraper and cotton buds, but I'm worried that I will just shift the crap on the outside of the carb inside the carb. Perhaps the best approach is to take it outside and give it a good blast with carb cleaner?

 

Any advice or tips on diagnostics/work much appreciated!

 

Dan

[Macpherson]

Hi, a wee bit of compressed air should do that before you strip it, try to avoid blowing any shit into the carb...

and then carb cleaner when you've got it in bits....... Or what Frammo said will also work.

 

It's handy to be able to blow down the parts prior to reassembly but a certain amount of care is needed to not blow stuff away.

 

Over the years I've had a many of these screws rattle loose on various saws new and old, so probably not easy to attribute blame...but there's a good chance their being gone is at the heart of your problem,  cheers.

[coppicer]

Just now, frammo said:

nb on safety note keep bar and chain on saw if you are going to rev it

Agreed, and I normally would, but I was checking whether the chain oil was being pumped through the oilways. There doesn't seem to be a lot, but some is coming through.

[coppicer]

3 hours ago, Macpherson said:

Hi, a wee bit of compressed air should do that before you strip it.

Just remembered that my dad left me a compressor which has been sitting in a dark corner of the shed since he died a few years ago. Spent an hour finding the bits and reading the manual, connected it all up and - result! Not very good at producing a consistent flow of air, but a little patience yielded results. I then lugged down the saw body itself and blew all the dust off that too. Therapeutic!

 

EDIT: attached photo

 

 

 

Edited July 18, 2020 by coppicer

[spudulike]

These saws tend to leak oil from the rubber pipe underneath the saw where the oil tank connects the oil pump. The smoke could be oil burning off the clutch drum. It is worth checking the clutch springs, if they are slack, they can contact the drum and produce heat.

Unlikely for anything to fly off when revved as it is an inboard clutch but....there is always a first time!

The carb - probably the most common issues are crap in the gauze strainer , perforated or distorted pumping diaphragm, weak needle valve spring and hardened metering diaphragm.

Your carb has had the limiters removed, make sure it is set correctly - 1&1/2 on the H screw and 1 turn on the L screw.

[coppicer]

1 minute ago, spudulike said:

These saws tend to leak oil from the rubber pipe underneath the saw where the oil tank connects the oil pump.

 

Your carb has had the limiters removed, make sure it is set correctly - 1&1/2 on the H screw and 1 turn on the L screw.

I have removed the handle. Saw no longer recognisable as a saw. Starting to sweat a bit.

I will check the the carb screws, thank you.

Unbelievable amount of crud built up in various nooks and crannies inside.

 

[coppicer]

Oil pickup body looks OK to the naked eye. Shone a bright light from behind it, and the holes seem clear.

Can't see any way to check oil pump. The service manual says I need Stihl installing tool 1123 890 2202 and upwards of £40 seems a bit expensive for something I may only use once...

 

[coppicer]

32 minutes ago, spudulike said:

Your carb has had the limiters removed, make sure it is set correctly - 1&1/2 on the H screw and 1 turn on the L screw.

spud, re "1&1/2 on the H screw" the manual claims 1 turn is factory, is this not recommended - too lean/rich as a default? I have set to 1&1/2 and it seemed to be screwed out more than that when I wound it in to the stop.

 

[Ratman]

probably dirty oil feed filter...i dont work on small saws but sure somewhere here will point you in right direction[emoji106]

Thats a bit sizeist! [emoji6]

[spudulike]

My chart says C1Q S121 or 122 is 1.5 turns on the L and H is 1 turn.

The MS181 has changed over the years, the initial saw was non Strato, yours is the later model. If you are using the handbook that came with the saw, go with that otherwise use my setting if you have the S121B or 122B carb