Cleaning carb on smoking Stihl

[bmp01]

Metering arm lives under the metering diaphragm, requires the carb to be pulled apart...

IIRC its a Zama carb on these, the Zama website is quite helpful if you can tolerate some reading and pondering.  There's a full explanation of how the carb works on choke, part throttle and open throttle plus the pump and metering arm layout. ...

Head to http://www.zamacorp.com/ then look for SUPPORT, then TECHNICAL SUPPORT then DISSASEMBLY AND SERVICING (types C1U etc).

Down the page you'll see this:

 

 

It used to be you could download this technical guide, not sure that's possible now. 

Anyway,  that's the metering arm stuff,  you need to decide if it's the type A or B, can't remember.

Whie you're in there, there's the filter to attend to. 

Pretty sure you can check the main jet one way valve in situe by accessing one or t'other drilling while closing high speed screw.....

 

Edited August 3, 2020 by bmp01
Further info added below image

[coppicer]

Thank you @bmp01 that's very helpful - didn't think of looking at Zama's site.

Have printed out that page and am studying it.

[bmp01]

Added a bit more to that post as an edit....

[outonalimb]

I'm guessing the best thing that could happen to this saw is to chuck it in the bin and buy an decent saw.(Just saying).

[coppicer]

32 minutes ago, outonalimb said:

I'm guessing the best thing that could happen to this saw is to chuck it in the bin and buy an decent saw.

Fair point, but I can't say I agree. The basic problem - I think - is that I'm a ham-fisted mechanic without much experience under my belt.

 

The saw itself is seven years old, been used by an unskilled owner and not maintained well. It hasn't been worked hard by arb standards, but it's put in some hours, albeit sporadically (sometimes I don't use it for months). For a non-professional saw, it's not done too badly. The owner, on the other hand...

 

I agree that a more powerful saw would be nice, something not too heavy, perhaps an Echo 501. On the other hand, at the end of the day, this is mostly a hobby for me. I cut wood and drag bits of tree about because I enjoy it. I don't want to drop wll north of £500 on a new saw the current economic climate. Work-wise, I'm keeping my head above water, but the floods have only just started and may get considerably worse before they get better. I might need that £600 before things get back to normal.

 

Edited August 3, 2020 by coppicer

[outonalimb]

I'm basically in the same position but have learned enough not to waste money on inferior tools.  

[coppicer]

1 minute ago, outonalimb said:

I'm basically in the same position but have learned enough not to waste money on inferior tools.  

I dislike poorly made things, and I hate having to buy twice. For most of my life I have by default bought quality tools, things like Snap-on, Knipex, Wera, Ko-ken, Silky, and a few other Japanese brands. I have gradually come to realise that quality is not equally valuable for all tools. Sometimes "good enough" really is good enough. I didn't think I'd be using a saw often enough to justify professional kit, and I assumed the MS181 would do what I needed it to do. And for seven years, up until a couple of weeks ago, I've been right.?

 

[coppicer]

Work a bit quieter, so back to the saw. Whipped off the carb (always wanted to say that!) and found fuel in the bottom. Using a magnifying glass, I set out to look a the metering arm as recommended by @spudulike. The inlet needle seems to be moving properly, and the spring doesn't look bunched. However, the metering lever does look a bit low, and when I depress it the needle doesn't seem to rise much. So maybe I need to pry that up as suggested in the Zama docs that @bmp01 kindly linked to earlier. Hard to get a good photo, but for what it's worth:

 

So that's one thing to try. The second possible issue is the fuel filter. The old one looked OK, but I didn't realise how fragile it was and I damaged it while removing, so I replaced it. Perhaps I didn't position it very well - it looks a bit skewed in these photos.

 

 

Forgot to say earlier - when removing the carb a rubber ring came off, which seems to have fitted between the filter base (carb bracket) and the carb itself. I think it is the No.12 "Stihl sleeve" in this diagram. Could that have been loose? Seems unlikely with the bolts pinched up correctly.

 

Plan of attack: adjust metering arm so it lifts needle higher; make fuel filter level and flush with bore in which it sits.

 

 

[bmp01]

No12 is a metal ring that plugs into the rubber manifold. I think its no 5 - which seals the reference pressure on the metering diaphragm to the pressure in the air box. Otherwise it would be referenced to atmosphere, (how older saws are). Its a simple dodge, to try to correct fueling when the air filter is partly blocked. Cant see it making much difference at idle, clean filter situation.

 

So, fuel in the pump but not the metering side eh ? Obviously you did get fuel in metering side (on choke) or it wouldn't have run at all. Then again saws been stood for a few days so maybe evaporated off, not conclusive.

 

[coppicer]

45 minutes ago, bmp01 said:

No12 is a metal ring that plugs into the rubber manifold.

This one feels like plastic, not rubber (or metal). Will have a poke around.