Stihl ms-170 cord stuck (different?)

[ScotiaMcBlurty]

Hi guys - sure you have all seen this one before, but nothing out there totally matches my symptoms, so here goes....

 

- Stihl ms-170, 7 years old, been good as gold for years

- Not used for 3 months

- Starter cord stuck

- Take plug out, cord turns easily.  So my thinking is to look for an exhaust blockage.

- Muffler is indeed dirty black, but can't see any blockage.  Taken it off, piston looks clean / sliver, rings visible, no blockage, moves freely.  Interestingly, there is no gasket between cylinder and muffler, just a metal plate which kind of surprised me. (???)

- Put plug back in, kept muffler off ... still cant pull cord ... so it's not a muffler blockage

 

What options are left ... blockage from the carb? 

 

Any thoughts appreciated - hate to give in and take it to a dealer - probably cost me more than the saw is worth   Not an expert on this, but happy to get stuck in.  Cheers!

[pleasant]

A long reach plug where it should be a short reach?

 

A 'blockage' in the exhaust or intake wouldn't cause those symptoms. If it pulls over perfectly well with no plug in- if it were a hydrostatic lock, then all excess fuel mix would be expelled whilst pulling it over with no plug fitted, so you can discount that. Unless you have a stuck metering valve in the carb and its simply filling the bore with unburnt fuel, and it is filling up so quickly that it is nearly full by the time you have refitted the plug. Do you get shed loads of fuel mix flying out the exhaust port and the plug hole when you pull it over?

[ChrisNewport]

Sounds like hydro lock with an excess of oil in the cylinder and i seem to recall this has been a question on here previously with the exact same symptoms and @spudulike diagnosed it correctly. The solution to spray a good amount of WD40 or Carb cleaner down the plug hole and leave it for 10 mins and then pull it over with the exhaust off and plug out whilst holding the saw upside down so whatever you sprayed in comes out of the plug hole and exhaust port then refit exhaust and plug and try and start it.

 

The no gasket is how they are and the metal plate is a heat shield.

Edited June 20, 2023 by ChrisNewport

[ScotiaMcBlurty]

Thanks guys. 

 

-No fuel coming out of exhaust port when I tug the cord with the plug out, so assumed not a hydro lock (?). 

-Did see one of Spud's posts - hence I turned it upside down last night, even after a couple of hours, not much had dripped out of the plug port

-Even with the plug only screwed in a rotation or two I get the tight cord, so plug probably not too long   

 

Have attached a couple of low res photos ... plug was a bit manky when I took it out (on the outside) - and perhaps leaking....  (That photo was taken before I turned the saw upside down).  Muzzle filthy. 

 

Its been good as gold until this issue.  Dealer serviced it a couple of years back, but suspect they just change the filters and not much else. 

 

Will try the WD40 as you say Chris .. can't harm.  Let you know how that goes - appreciate the help guys.  

[Mick Jones]

Hard to be certain but the plug on that picture does look to be a long reach?

[Mick Jones]

1 minute ago, Mick Jones said:

Hard to be certain but the plug on that picture does look to be a long reach?

off the top of my head the plug should be NGK BPMR7A

[pleasant]

10 minutes ago, Mick Jones said:

off the top of my head the plug should be NGK BPMR7A

That is correct.....bprm7a is a short reach plug. Unless that photo is deceiving that plug looks like a long reach.

 

However...I am sure the OP would have said he has just changed the plug and now it doesnt pull over.....surely????

Edited June 20, 2023 by pleasant

[ScotiaMcBlurty]

Will check the plug serial # at lunch.  Its been in there since the last service ... but that's doesn't mean to say its not right!   

[pleasant]

....but it wouldn't have run since the service if it were too long in the reach. You say it has been running with it fitted, so cant be the plug. The point being made if the plug is too long it would foul the top of the piston...hence the symptoms you have.

Edited June 20, 2023 by pleasant

[ScotiaMcBlurty]

Right, the plug I have is a NGK CMR6H.   Have dug out the manual and its the right one. Book says

 

     Spark Plug (Supressed) : Bosch USR4AC, NGK CMR6H.  

 

Which does make sense, as even if I just cover the hole with my finger, the cord still goes tight.  Will try the WD-40 wash out tonight.