Pete

[Pete H]

Good evening all,

 

I’m Pete from Bersham near Wrexham North Wales.  I’m a newbie here so be gentle, I’ve been a chainsaw user for many years mostly for home/farm use for trimming back and firewood. I have always maintained/repaired my own equipment, replacement of chains bars and dismantling of carb for running issues etc.

However, I have a problem with a MS 260 which my son bought second hand, it’s an old saw and up until now has never really been a problem.  I was experiencing starting problems leading up to this.

My reason for asking you professionals is that after cleaning the carb many times it starts, bogs down and in my opinion screams at high revs (weak mixture).  

After “rooting” around I believe that the carb fitted is incorrect, WT394.  Contacted Sthill and they have no record of my saw?  I know that the simple answer would be replace the carb but this is a puzzle I would like to get to the bottom of.  I was a mechanic by trade and my preference is to repair rather than replace, that to me is the easy option.

My apologies for an initial lengthy post, but I would be extremely grateful for some input/advice on this.

Thank you all,

Pete

 

[Stubby]

38 minutes ago, Pete H said:

Good evening all,

 

I’m Pete from Bersham near Wrexham North Wales.  I’m a newbie here so be gentle, I’ve been a chainsaw user for many years mostly for home/farm use for trimming back and firewood. I have always maintained/repaired my own equipment, replacement of chains bars and dismantling of carb for running issues etc.

However, I have a problem with a MS 260 which my son bought second hand, it’s an old saw and up until now has never really been a problem.  I was experiencing starting problems leading up to this.

My reason for asking you professionals is that after cleaning the carb many times it starts, bogs down and in my opinion screams at high revs (weak mixture).  

After “rooting” around I believe that the carb fitted is incorrect, WT394.  Contacted Sthill and they have no record of my saw?  I know that the simple answer would be replace the carb but this is a puzzle I would like to get to the bottom of.  I was a mechanic by trade and my preference is to repair rather than replace, that to me is the easy option.

My apologies for an initial lengthy post, but I would be extremely grateful for some input/advice on this.

Thank you all,

Pete

 

Hi Pete . If its racing I would investigate a possible air leak . Split fuel pipe split carb to air intake boot knackered crank case seals etc etc . Hope you can sort it .

[Dan Maynard]

Have you found LS Engineers? You just need to register on the website (free) to see parts diagrams

https://www.lsengineers.co.uk/stihl-ms260-chainsaw-spare-parts.html

 

They are also pretty helpful on the phone, even if it's just small parts like Stubby said.

[ChrisNewport]

MS260 with a good few years behind it, id be checking the flywheel side crank seal.

[Wonky]

2 hours ago, ChrisNewport said:

MS260 with a good few years behind it, id be checking the flywheel side crank seal.

I think you mean the pto side, that’s the seal that tends to go first.

 

i would also check the impulse. But if it’s old as.. it may be good insurance to change both (edit) seals

that little one can be a pain to get out though.

 

 

Edited May 26, 2022 by Wonky
Edit

[ChrisNewport]

1 hour ago, Wonky said:

I think you mean the pto side, that’s the seal that tends to go first.

 

i would also check the impulse. But if it’s old as.. it may be good insurance to change both (edit) seals

that little one can be a pain to get out though.

 

 

no, i mean the flywheel side.

[spudulike]

All very interesting but it is most likely the impulse line has come off the brass union just under the cylinder base.

You won't understand so....if you look between the air box that holds the carb and air filter and the cylinder back under the spark plug/ inlet manifold (rubber tube thingy), you will see a rubber hose (like a fuel line)that comes out of the rear of the air box and should be pushed on to a little brass connector that is just under the inlet manifold and just under where the cylinder sits on the crankcase. 

You need either forceps or long nose pliers and push the line back on to the brass union. Fitting a new hose is probably best but the above will sort it. It usually comes off when the saw gets stuck in a cut and the operator gets a bit leery with the rear handle and over eggs the saw removal.

Why do I think this is the issue - I recently had three 260s in, all with the same symptoms and all had the same fault!

[Pete H]

Thank you all for your help, I really do appreciate it.  I can normally sort this type of stuff out but for fear of labouring a point my confusion is that Sthill uk say that the carb WT394 was not fitted to this saw.

Anyway, I’ll take all your advice and pull it out of the bin and try again.

pete

[Stubby]

1 hour ago, Pete H said:

Thank you all for your help, I really do appreciate it.  I can normally sort this type of stuff out but for fear of labouring a point my confusion is that Sthill uk say that the carb WT394 was not fitted to this saw.

Anyway, I’ll take all your advice and pull it out of the bin and try again.

pete

Don't you just hate God ? he will do anything to make shit awkward for you if he is board . Just to be clear hear , he has never liked me , we just don't get on . Now , he has seen fit to make my Sony 4K smart TV stop working . Sound but no picture . I hate him .

Edited May 27, 2022 by Stubby

[spudulike]

Back on track....seems Stihl have used a big variation of carbs on the 026 (predecessor to MS260) to the MS260 and there have been quite a few cylinder/piston types in the development of the model.

You may well have had a replacement carb or your saw may be a BITSA or Frankensaw but....I have often changed carbs from the later MS260 on 026s that were running poorly, often on the idle as these old carbs can sometimes just get extremely uneven on idle and swapping a carb out usually does it.

You originally said "until now has never really been a problem" so am taking the assumption that the saw was running well for a period of time..weeks, months years and now it has changed. This shows the carb was working on the saw and something has now changed.

You said you have cleaned the carb "many times".....I have seen carbs with gaskets and diaphragms in all sorts of order...one Jonsered almost killed me and was much fitter after I eventually found the pump diaphragm and gasket weren't fitted correctly. Sooooo - make sure the thin plastic pump gasket is closest to the carb body and make sure the gasket spacer sits BETWEEN the metering diaphragm and the carb body (this is the one with the metal disk on it). These carbs take a number of diaphragms and they have different height nipples in the middle of the disk and this can cause issues. Have you swapped out these components or are they as they were and if the gaskets were bonded to the top cover and the other one to the metering diaphragm, we should be OK.

The most common carb issue is a blocked gauze strainer - the little round circular stainless mesh thing - best pull it out and look at the open areas with a backlight and magnifying glass - I didn't many years ago and had the same saw back three times...sorry Matt.

As I said before....best check that impulse line before getting too involved for the reasons mentioned before. 

You can tell if your carb is one of the real old ones or not by the way they adjust up. The later H&L screws operate completely independent of each other. On the early ones, adjusting the L screw messes up the H screw. 

The carb settings should be 1 turn out on each screw (if limiters are not fitted).

If the carb has a H screw limiter (red, black or white plastic) it is a later model and these are the better ones. It will look like the image below: -