Did I eat some carbon?

[NH_Wood]

Hello all and Merry Christmas!

Been cutting with a Husq 55. Has always run excellent and ran perfect for about 4-5 tanks over the past week. Went to cut yesterday - saw started, let warm up at idle, but the moment I started a cut, began to bog. Tried to rev the throttle - had a bog as well as erratic idle - mainly a high idle (chain spinning at idle). Thought the low idle may have come out of tune - attempted to tune but still had the problem. Since it is an old saw (a 1998), although I keep in nice shape - figured I might have blown a crank seal (they've never been changed). Pulled the muffler to take a look - figured piston would look great as always, but....here is what I see. Top left view from port shows some erratic scratches and you can see brown discoloring around that area. My thought is a ate some carbon at some point when I cut a few days ago. Do you all think this level of damage would be enough to cause the behavior I described? Wondering if I should start with a top end repair (possible base gasket leak would be a non-issue with a new gasket) and see if the problem is solved. If not, then think about crank seals. Thanks for your thoughts! Cheers, Jacques

 

[Tobystihl]

It's piston ring blowby, caused by worn rings.

 

[Mad Professor]

It's piston ring blowby, caused by worn rings.

Looking greasy and overly rich to me.

 

[Marley5]

Did you check check the spark arrestor screen ?

 

[NH_Wood]

Thanks - I do run 45:1 but try to keep tuned at 12500. Are scratches to minimal to cause this issue? I've been running the saw exactly the same for years and it's been great. Screen clean - but would a clogged screen cause a sudden high idle - I could see the bog. Can pop on a new ring as I go through it - assuming the scratches aren't too bad. I guess I'm looking for thoughts on why the sudden change. Thanks all!

 

[farmguywithasaw]

Thanks - I do run 45:1 but try to keep tuned at 12500. Are scratches to minimal to cause this issue? I've been running the saw exactly the same for years and it's been great. Screen clean - but would a clogged screen cause a sudden high idle - I could see the bog. Can pop on a new ring as I go through it - assuming the scratches aren't too bad. I guess I'm looking for thoughts on why the sudden change. Thanks all!

Not to start one of those oil threads what do you use for mix

 

[farmguywithasaw]

By the sounds of it it could be a vacuum leak. I would start with a basic tune up. Clean carb do fuel filter/line and spark plug. Blow out the air filter ectra. I have a feeling your filter screen has **** in it

 

[alexcagle]

That is microsopic wood particulate that has accumulated and carbonized.
Or.....Too rich. Not a full burn.
25% of the fuel in some 2 smokers goes out of the exhaust.
When you shut off mr chainsaw, it may have a wet piston that dries into varnish from heat after shutdown. Then when you run it the next time it turns black.
That or your fuel volatility might be too low.
My gut says wood and or dust accumulated.

 

[Gord404]

what color is the spark plug- indicator of how it was running

 

[NH_Wood]

Not to start one of those oil threads what do you use for mix

I bounce between Belray and VP

 

[NH_Wood]

what color is the spark plug- indicator of how it was running

It was dark - looks like it's running rich.

 

[NH_Wood]

That is microsopic wood particulate that has accumulated and carbonized.
Or.....Too rich. Not a full burn.
25% of the fuel in some 2 smokers goes out of the exhaust.
When you shut off mr chainsaw, it may have a wet piston that dries into varnish from heat after shutdown. Then when you run it the next time it turns black.
That or your fuel volatility might be too low.
My gut says wood and or dust accumulated.

Thank you!

 

[NH_Wood]

By the sounds of it it could be a vacuum leak. I would start with a basic tune up. Clean carb do fuel filter/line and spark plug. Blow out the air filter ectra. I have a feeling your filter screen has **** in it

Will do - especially with the advice that the 'scratches' are not likely piston damage but carbonized wood. Will do a full tune up and if it persists, will bring it to the shop for a pressure/vac test. My favorite part about theses saws are the ease of breaking them down and putting them back together! Thanks!

 

[NH_Wood]

Thanks for the replies everyone - gives me a lot of places to look. Haven't run my 61's in awhile - now I have an excuse

 

[steele_109]

I would check for a air leak behind carb.It's a common problem with this family of saws.It would cause the symptoms you mentioned.Or the impulse pipe is leaking both are behind the carb.Take the top cover off and air filter crank the saw, use a can a break or carb clean with a straw. Spray behind the carb if the running changes,you found your problem.The impulse is in the base of the cylinder on the lower left behind the carb.

 

[Gord404]

I would check for a air leak behind carb.It's a common problem with this family of saws.It would cause the symptoms you mentioned.Or the impulse pipe is leaking both are behind the carb.Take the top cover off and air filter crank the saw, use a can a break or carb clean with a straw. Spray behind the carb if the running changes,you found your problem.The impulse is in the base of the cylinder on the lower left behind the carb.

ya that impulse setup has been a leak problem cause over the years it no longer fits tight in the rubber boot- had a mint 1989 -51 last year come in with a bad top end last year and that was the cause and a few others over the years

 

[Chevboy0167]

Impulse tube loves to rub on the intake boot and cause a hole.... equals lean condition.

 

[NH_Wood]

Even though embarrassing - I think it's worth updating with the solution for all that will read in the future! I jumped to major issues too quickly. As I broke down the saw, the fuel line had become very hard - the fuel filter was also getting dark - but I think the fuel line was the main issue. Changed the line and filter and she's running like a champ. Thanks for the responses - goes to show - check the simple things first! Also - I forgot that I lost the spark screen years ago - so that definitely wasn't the problem . Appreciate the responses the help diagnose the issue - this saw is my main saw that I grab to cut and it just does what it's meant to do - glad to have it back in good running condition. Thanks all - Merry Christmas and Happy New Year!

 

[buzz sawyer]

Glad you found the problem. When a saw suddenly runs faster with no change in the throttle opening, it's either getting less fuel or more air. I would still do a vac/pressure check based on the age of the saw. It's probably ok, but then you know for sure.