Stubby’s opinion please

[Baldbloke]

Recommendations for larger strimmer

Update on the misfiring Stihl FS 460.

Took it back to my local dealer (who to be fair was willing to take it back) and found that the plug had picked up some

(carbon?) deposit between the electrodes. Cleaned it off and off it went again. The engine fires up first pull from hot and second pull from a cold start as it should. It appears to have good compression. Replaced the plug and took it home and used a tankful of mix. The new plug also picked crap between the electrodes after about 15 minutes.

Just wondering if this is carbon off the exhaust port finding its way into the combustion chamber and this might be it on its way out?

 

 

https://arbtalk.co.uk/index.php?/topic/110610-Recommendations-for-larger-strimmer/page__view__findpost__p__1636553

[Stubby]

Mmmm . If it has good comp then I don't think it is on the way out . Could have been run rich , or with a higher oil to fuel ratio for sometime in the past resulting in the carbon deposits . Might be worth taking off the muffler and cleaning it out .  As said use the correct heat rang NGK plug and use modern high quality 2T oil at 50:1 in your mix . To avoid carbon build up in a new machine use an alkalite   fuel such as Aspen or Husqvarnas own or Stihls own .  Probably too late on this one unless you go to the expense of changing all the rubber components .  Also get the carb set up by someone who knows what they are doing .

[Baldbloke]

Thanks for your input. [emoji1303]Will give the exhaust port a look. Also get a compression test done as the elastic pull on this model is maybe deceptive. It does hold noticeably on the pull cord drop test.However, when the plug isn’t hard fouled the engine idles and performs like a good un. Replacement spark Plug is the Recommended make and heat range. Husqvarna low ash synthetic 2 T oil. Fresh petrol and mix. It runs beautifully when the plug gap isn’t compromised by what I suspect is hard carbon crap.

BTW: I do understand it has sat idle for a while.

[bmp01]

This "hard carbon" you mention, are you saying its a lump of carbon that's maybe come off the combustion chamber and has wedged itself between the plug electrodes ?    And its done it twice ? 

On the other hand fouling a plug to the point where its completely carboned up within the space of one tank of fuel is pretty much unheard of too (with modern oils)....

 

Maybe it's just cleaning itself out after previous misuse, it might also be spitting carbon out of the exhaust too, just thinking about the spark arrestors on saws in USA.

 

[Baldbloke]

After I’ve done some drainage works today I’ll see if I can remove the muffler to get a better look at the piston and ring(s)

[Stubby]

10 hours ago, bmp01 said:

This "hard carbon" you mention, are you saying its a lump of carbon that's maybe come off the combustion chamber and has wedged itself between the plug electrodes ?    And its done it twice ? 

On the other hand fouling a plug to the point where its completely carboned up within the space of one tank of fuel is pretty much unheard of too (with modern oils)....

 

Maybe it's just cleaning itself out after previous misuse, it might also be spitting carbon out of the exhaust too, just thinking about the spark arrestors on saws in USA.

 

Yep . If it has a spark arrestor mesh I would remove it anyway .

[Baldbloke]

Yep . If it has a spark arrestor mesh I would remove it anyway .

Will do[emoji1303]

Out of interest, If I manage to remove the muffler I’ll take a picture of the port and what’s viewable of the piston, its skirt, and ring(s)

[bmp01]

18 minutes ago, Baldbloke said:

Out of interest, If I manage to remove the muffler I’ll take a picture of the port and what’s viewable of the piston, its skirt, and ring(s)
 

 

 

Picture of the plug with the carbon stuck in it would have been good,  one for the library that. ...

[Baldbloke]

Never thought to take a picture of the plug with offending carbon but have taken some of the exhaust port
No spark gauze that I can see in the muffler.

[Baldbloke]

You can just make out on the first picture some build up on the lowest edge of the port. No scoring on the piston skirt but some discolouring below the rings.
Think I’ll run another tankful through it and see if I can blow the cobwebs out of it[emoji1303]