281 dead, will not start

[JohnAlbers]

281 stopped running and will not start

I just got my 281 saw back from having some basic work done on it along with the carb adjusted. I have run this saw before but this past weekend was going to be the first time cutting with it. The chain was just sharpened, 20" bar, winter grade Husq. bar oil, 93 new gas, Husq oil mixed 38:1. Open the port inside the top cover to allow warm air from the engine to preheat intake air going through the air filter. It was Saturday cold 25F with a little snow. I started the saw, not easy since no decompression switch. I let the saw run slow for a good 15 min. so it was up to temp before using it. I was going to cutting a stump about 40" in dia. I started cutting and before I knew it the bar was dead into the stump without any change in sound or power. I pull the saw out and I let of the trigger and it died. I set it on the ground and it started backup real easy without much force, maybe because it was warm? I cut another 5-8 min. and pulled the saw out to move to a different area and let go of the trigger again, stopped. One again it started back up again. I was thinking maybe the carb was adjust too low and that is why it was dieing on me. I cut another 5min. and it died in mid cut, like it ran out of gas. I check tank half full or better. I top it and the bar oil off and still would not start. The rope was real easy to pull. I could hear the piston, I think, going up and down and valves opening. I waited about and hour and tried again, nothing. I used another saw of mine to do some other cutting and did not touch the saw for a good 7-8 hours. The rope was still real EASY to pull. It has never been like this. Any ideas what went wrong? Did I blow the engine or something? Thank you for any help you can give me.

John

 

[TimberPig]

Sounds like the carb was set too lean and you seized a piston. Pull the muffler and take a peek at the piston and rings. If the rope is really easy to pull like you say, you're going to find a scuffed up piston.

Two stroke engines are lubed with premix, and are very sensitive to the air/fuel mix ratio delivered. If it is too lean, the piston gets too hot, causing it to melt and seize to the cylinder wall. Often when it cools, the piston frees up, but is damaged and requires replacement to run properly again.

Essentially yes, you blew your engine, in commonly used, although nondescript language.

 

[JohnAlbers]

TimberPig,
Does that mean I need a new piston or what. I just got the saw not too long ago and had the work done by a Stihl/Husq dealer, do not know the knowledge of him. I had to replace the gear spacer near the clutch. He said he did that and adjusted the high side of the carb. I told him today what happen and he said to bring it back in. He told me that I should not be running 38:1 that will mess up the plugs and plug the spark screen. Is there anyway to tell if the damage was happening before and it just happened or from the guy that adjust my carb? Thanks.

John

 

[TimberPig]

Yes, most likely the piston is done and has to be replaced, possibly the cylinder and more, depending upon the extent of the damage.

What is more likely the cause is that the saw was set for a warmer temp than you ran it at. Cold air is more dense, contains more oxygen per unit of volume, and needs more fuel by way of opening up the mixture screws on the carb, to maintain the correct air/fuel ratio. Since you didn't do this, then ran it hard, it was lean from the cold air, and the hard running demanded a richer mix than you were providing, and thus the seizure as the piston overheated and stuck.

Your mix is fine, but the probable cause of this is operator error, not the guy who tuned the saw for a different temperature. It is unlikely it was caused by the tuning your dealer did. He tuned it correctly for the conditions in his shop, you then used it in different conditions which caused it to run lean. I'm afraid to say it, but you are likely to blame for it.

 

[NWCS]

if your dealer tuned the carb with 50:1 mix and you ran 38:1 without retuning the carb for that thicker slower flowing mix, she was running lean and probly scuffed the piston and destroyed the rings. each time you change the mix ratio the carb must be tuned to that ratio. the easiest way to think of this is look at motor oil, 10wt flows out of the bottle faster than 20wt, and that 10wt flows much faster than 30wt. the same goes with fuel mix through the carb, the more oil in it the slower it goes through those tiny little holes in the carb. thats why the carb has to be tuned to the specific ratio your going to run. just a tiny bit thicker makes a lot of diffrence.

 

[JohnAlbers]

Are you saying that I need to have the carb set for different outside temps? How much of a temp change matters. When he would have worked on the carb it was at a 32:1 mix which is what I thought many people here say that they run because of better protection.

If it is more than a piston and rings what all could it be? Do you have any idea what I might be talking price wise? Thanks.

John

 

[Stumper]

The difference between mix ratios doesn't ammount to much. John -I don't know what is wrong with your saw but I wouldn't jump to any conclusions.-Get it checked out by someone you can trust.

Scuffed pistons don't necesarrily suddenly get easy-but stuck or broken rings could cause a sudden drop in compression-Whatever has happened it can most likely be repaired.

 

[NWCS]

if its just the piston and rings, that is $35 for an aftermarket one, the cyl can probly just be honed out to fix it. thats about $15 or so. you might have whoever does the service also check the crank seals. bad crank seals can cause some eratic running and create all sorts of engine issues, including taking out the piston like that. without looking it over in person its hard to say for sure what it was.

 

[JohnAlbers]

Thank you for all your help. I took the saw back to the dealer today. He said he will have to get into it a little more but the piston and cylinder are damaged but we do not know how bad. He is thinking at this point about $250 unless it needs a new cylinder then over $500. This could be an expensive lesson to learn. Thanks again.

John