Screws In The Breather Hose

[TomGraz]

My Stihl 025 hasn't been running well lately. It would start and run for 30 seconds and stop. Then it wouldn't start again until it completely cooled - or so I thought. Two trips to two different small engine shops, and it cut for maybe 10 minutes. Then the same thing, it wouldn't start again for quite a while. A neighbor cutting wood out of his yard saw me struggling to start the saw and offered to take a look because he "does all his own work". We noticed the fuel tank has a breather hose that extends about 1.5" and has two screws inside it. We removed it and the saw started and ran great for about 20 minutes. Then it wouldn't start again.

I'm assuming the screws in the hose allow air to flow into the gas tank while keeping gas from spilling out? The hose was very aged - it broke in a couple of places. You couldn't blow air through it. I'm wondering if there was a pressure problem in the tank. Like if air couldn't get in gas wasn't getting out? If that is the case, could the last shop have tuned it incorrectly?

Any thoughts are appreciated.

TG

 

[Little Al]

Is it possible to run the saw with the gas cap off ? if yes try that & see if it cures the problem. If the saw runs OK like that renew the breather pipe/tube & retry some saws have a duckbill valve in the breather line I'm not up on this model of saw to know if it does/should have. If the saw runs OK while it's running that would seem to rule out faulty set up/tuning I would set up the mix screws on the carb if you know the settings that will eliminate that & then do one thing at a time trying to run it after each thing done. Case of elimination "till you find the fault.

 

[HarleyT]

Examine closely the fuel line for cracks between the tank and carb. Go ahead and pull off your muffler and look at your piston for damage.

 

[blsnelling]

Here's another example of why not to use grub screws for a tank vent.

 

[HarleyT]

Why is that? He says that the saw won't start now.

Even if he was to change vent styles, what would you recommend? And how. etc....

 

[SteveSr]

Even if he was to change vent styles, what would you recommend? And how. etc....

These saws can be retrofitted with the new style tank vent which won't leak or stop up like the old grub screw. See...

http://www.arboristsite.com/community/threads/stihl-grub-screw-tank-vents.299786/

However, I doubt this is the root cause of the OP's problem.

 

[Whiskers]

A saw ceasing to run after 10-15 minutes could be a bad coil. Next time you run the saw check for spark when it won't start.

 

[HarleyT]

These saws can be retrofitted with the new style tank vent which won't leak or stop up like the old grub screw. See...

http://www.arboristsite.com/community/threads/stihl-grub-screw-tank-vents.299786/

However, I doubt this is the root cause of the OP's problem.

Yeah, I remember that thread. That was me in it....
That was me that said that one could just use the newer style.




I was asking Brad, I just wanted him to explain how this would work:
Because that is what he suggested that time.....

 

[blsnelling]

Yeah, I remember that thread. That was me in it....
That was me that said that one could just use the newer style.




I was asking Brad, I just wanted him to explain how this would work:
Because that is what he suggested that time.....
View attachment 532122

Still working that one huh? Time to get some new material isn't it? I was referring to a different model. You'll catch on someday.

 

[HarleyT]

Yeah, both posts were started about 025 series saws. You didn't explain how you used that part on an 084 either...

 

[HarleyT]

You still never explained how you used the flapper, on a saw that previously used the grub screw vent.
If it is an easy fix, or even a difficult one, why wouldn't you show it to the forum?

Especially since you are constantly preaching your gospel according to St. Flapper....

Seriously, show the folks how to install it, if you truly wish to "educate". If I had an 084 or two around, I'd be taking photos to put up, just to show the folks. I had an 026 that I took photos of for that other thread, and the flapper has to be used on a fuel tank that is made for it.

 

[TomGraz]

Just a follow up. The problem was indeed the gas tank breather vent tube. I'm guessing that over many years, the hard rubber/soft plastic tube degraded and the inside pressed into the threads of the screws. That condition didn't allow air to move past the screws to equalize the pressure in the tank as gas was drawn out. As my father, the 30 year Air Force mechanic, would say, "You've got a vapor lock in the fuel line". (I heard that so much growing up I use it to explain problems with computers I work on.) The first place I took it to didn't catch the clogged vent and apparently tuned the saw as though it was starving for gas. The second place replaced the vent tube with a newer style, what the guy called a "duck bill", to keep gas from spilling out. He tuned the saw properly and it's been running like new since I got it back.

I want to give a shout out to all the good shops out there. The guy warned that since the carb had never been replaced, it would probably have to be. I told him that if the bill got beyond $100, I'd opt to spend that on a new saw I was eyeing on the shelf. He said he understood and would see what he could do. As luck would have it, I didn't need a new carb. I'm adamant about using non-ethanol gas with a stabilizer. It cost a whopping $42.50 for parts and labor. The guy could have worked me into a higher repair, or a new saw. What he did was secure a new customer that told all his friends how well he was treated. When I'm ready for that bigger saw, I'm driving past 3 big box stores to his place. You know... the north coast of South Carolina is called the Grand Strand...

 

[trappermike]

A note about those breather hoses with the 2 screws in them. If you ever tried blowing thru one you will notice you cannot. Hence the potential for fuel starvation problems... As a saw mechanic I modified every one ever worked on,and modded them on new saws too to prevent any future problems..
Remove both screws from the saw,then throw 1 screw away.Take the other screw and with a fine toothed hacksaw,gently cut a shallow groove down the length of the screw,don't even cut completely thru the threads,about halfway.Put the screw in the hose and test blowing thru it,you should just be able to feel air passing slowly thru it,make the cut too deep and the hose will tend to be leaky(gas),if you've gone too far,take the discarded screw and groove it a little less.

 

[a. palmer jr.]

I'm kinda interested in trying out the hose and bulb thing that Echo uses. It looks like it would fit on many Stihl models. Of course you could always drill a hole in the top left side of the tank and insert a duckbill valve like Homelite does..

 

[trappermike]

Some of the Stihl fuel tanks had a little orange 1 way valve under the tank breather hose. I just modified the screw to breathe well to prevent any potetial problems,one less thing to worry about.
On the 2100 Huskys I would use the vented oil cap on the gas tank.
Stihl used to use the threaded screw in the gas cap of older models for a tank vent,these easily got plugged by sawdust and snow and ice,I modified those too.

 

[a. palmer jr.]

Some of the Stihl fuel tanks had a little orange 1 way valve under the tank breather hose. I just modified the screw to breathe well to prevent any potetial problems,one less thing to worry about.
On the 2100 Huskys I would use the vented oil cap on the gas tank.
Stihl used to use the threaded screw in the gas cap of older models for a tank vent,these easily got plugged by sawdust and snow and ice,I modified those too.

Think I had one of those on an 015 top handle. I got the needle nose pliers out and wallowed the screw around until it vented.

 

[SteveSr]

A note about those breather hoses with the 2 screws in them. If you ever tried blowing thru one you will notice you cannot. Hence the potential for fuel starvation problems...

I don't really think that this is a fair test as a functional flow rate is VERY low. The only real way to tell if it is working is with a Mity-Vac (or similar) and watch the pressure drop on the gauge.