Sudden Problem with my 026

[sritzau]

Today I had a problem with my heretofore very reliable 026. I refilled my tank and went back to cutting. Everything started as normal, but as I ran for a while (maybe 5 minutes) it started to rev a little higher (almost like it was running lean) and then went into a mode where it would idle fine, but if I pulled the throttle trigger it would sound bogged down (even though it was not in any wood). I turned the saw off, checked for obvious problems and found none. I re-started it and it seemed okay. about 5 minutes later, it repeated with all the same symptoms.

There is a gizzy on top of the tank that looks like allows air into the tank as the fuel is consumed. My novice guess was that this might be clogged and I might be creating a partial vacuum in the tank as I run it. I don't see signs that it is clogged - it's really just a guess. Any advice would be appreciated.

Steve

 

[glens]

It's certainly possible the tank vent is not working right.  Next time it happens, try momentarily popping the gas cap loose for a sure vent (with the saw still running) and see if the problem changes.

Is it really an 026 or are you saying that generically and it's an MS260?  How many hours or seasons on it?  It might be time for a general fuel system freshen-up.

Glen

 

[Kenskip1]

026 Problem

Steve,
When was the last time that you had a New gas filter installed? My guess is that the old filter is just clogged. If this does not solve your problem, take a look for a kinked gas line. I will make a bet, that if the saw sat for about an hour, that it would run great until the clogged filter has shown it's head. Keep us posted, Ken

 

[sritzau]

It's a MS260. I have had it for three years and have never changed the gas filter. Lately I have been running it a lot more than usual (i'm clearing a house lot). What would a fuel system freshen-up entail?

Thanks for the advice. I'll see how the saw runs tomorrow and (if things haven't changed) I'll try the "gas-cap-cracked" technique.

Steve.

 

[mikey]

I had my small limbing saw(41cc) suddenly start leaning out one morning.I adjusted the carb and for a minute it ran good,but then started leaning out again.To make this short,my saw was vapor locking.It was mid 80's temp wise with very high humidity.This may not be your situation,I'm only tellling of my experiance.Good luck with your 026!

 

[Kenskip1]

Steve,
Take the short and inexpensive route. Simply drain all the gas out of the tank. You may need a pair of needle nose pliers, or an old wire coat hanger with a small loop to get ahold of the gas line. Simply remove and replace the filter, gas her up and see how she goes! I had the same thing happen and the nearest dealer changed the filter. Cost 25$ back then.I am now wiser! Ken

 

[glens]

Originally posted by sritzau
What would a fuel system freshen-up entail?

What I had in mind was a carb kit (new diaphragms), fuel filter, checking the intake boot and impulse line, and giving the tank vent a once-over.

The check you're going to make will be the cheapest thing you can to at the outset.  The fuel filter would be next in line price-wise.  The "suddenality" of the change is a little puzzling if it's just the fuel filter, though.  Maybe a bit of foreign matter has gotten past the filter and is slowly packing against the screen in the carburetor during use.

I would caution to not spend too much time running the saw while it leans out, however.  If cracking the fuel cap "fixes" it, you probably can forego all the other stuff beyond the vent.  If that doesn't do it and it happens again, change the filter.  One more time and I'd go through the carb with a fine tooth comb.

230 KB document attached.

Glen

[edit:  wrong file was attached]

 

[glens]

Here's the vent stuff; 88 KB file.

Glen

 

[Gypo Logger]

In addition to what has already been mentioned,and the follow thru doesn't alleviate the problem, take the muffler off and check the jug and piston for scoring. Symptoms often manifest themselves only when the saw gets to operating temps. Scoring will inevidably raise operating temp. thereby causing erractic behaviour.
John

 

[sritzau]

It will be Wednesday before I can try any of this (too much other work). Thanks very much for the diagrams - they are great and now I understand what I am looking at a lot better. I hope it isn't the piston/jug... Steve

 

[Kenskip1]

026

Steve,
As two your problem, please do not over look the obvious. I think that your problem is simply a bad gas filter. As you stated that you refilled the tank and went back to cutting. This tells me that the cylinder and piston, rings are all fine. I will asume that you have been using the proper oil mix. I may be wrong however the filter is the simplist and cheapest thing to replace. A bad diaphram May be the culprit however this is a long shot. A crack in the gas line is another possibility. This will be hard to see. I do not know about your mechanical abilities, however the carburator is a very delicate instrument. I would not want you to have to take the saw in pieces to your dealer. he will charge you $$$. Look for a small crack in the gas line. This could be the culprit as well as the gas filter. Keep us posted, Ken

 

[stihltech]

fuel

When this problem hits the bench on an 026 the first thing I do is pick it up by the starter handle. If it holds the saw up, we have someting to work with. Pull it over, it should spin over a few times with a normal pull.
Then it is spark, then dump the fuel in a glass jar, checking for waterand old or contaminated fuel. Look at the fuel filter, replace it if you can't remember when it was done. Now stretch the fuel hose a bit. If you see any cracks or checking in it, REPLACE it. Check the pulse hose the same way.

Once in a while I will just go after the hoses, but I have been burned in the past by not checking the fundamentals first. We are talking 5 minutes in the shop, best time I spend on a repair.

 

[JimL]

Re: fuel

Originally posted by stihltech
When this problem hits the bench on an 026 the first thing I do is pick it up by the starter handle. If it holds the saw up, we have someting to work with. Pull it over, it should spin over a few times with a normal pull.
Then it is spark, then dump the fuel in a glass jar, checking for waterand old or contaminated fuel. Look at the fuel filter, replace it if you can't remember when it was done. Now stretch the fuel hose a bit. If you see any cracks or checking in it, REPLACE it. Check the pulse hose the same way.

Once in a while I will just go after the hoses, but I have been burned in the past by not checking the fundamentals first. We are talking 5 minutes in the shop, best time I spend on a repair.

Sometimes its the simple things that bite you in the ass!

 

[John Stewart]

Hey
Had the same problem once
Clogged spark arrester was the issue!
It is the little screen on the side of the muffler
Take it out and see if it runs better
If it does either take a propane torch to it and burn the crap out of it(Hang on to it with a pair of plyers) or just leave it off
If you are in a urban enviroment don't worry about starting a forest fire!
John

 

[sritzau]

I tested the saw yesterday and now I am pretty sure it's the tank air vent. It took a while for me to run the air out of the tank, and then - by cracking the tank cap - all went back to normal.

My only problem is that, after dissecting the valve and filter assembly, I didn't really find a "smoking gun". One of the vent holes under the valve looked partially blocked, but the other two were clear. The sintered filter does not look spic and span, but looks like it could pass air if it needed to. I will say that it did seem to be loaded with gas - maybe an indicator that the little vent flapper is not seating right.

Anyway, I am planning on replacing the little valve and the other little parts in the system. I figure I'll do the gas filter at the same time just because I'm in there.

Steve

 

[stihltech]

vent

Looks like you are on the right track. If you have access to a vacuum pump, a hand one will do, empty the tank, hook the pump to the hose, and see if you can pump it down. If it stays at a vacuum, the valve is the problem. If it bleeds off quickly, it is OK.

From the cap test, I would say it is holding a vacuum.

 

[sritzau]

Just wanted to report back that, after changing the gas tank vent filter and the gas filter, the saw is running fine. Thanks for the help! Steve.