# Chainsaws and vapor lock?



## avalancher (Apr 25, 2011)

I had a unusual occurence this past weekend, at least for me. Guy down the road had a large white oak he wanted down and gone, and I decided to take it down and haul it out on Saturday.It was warm, mid nineties, and i dragged along the 357XP for brush duty and the 372xp for the main stem.

After a lunch break, the 372 refused to start.It would pop, run a second then quite.Exasperated, i pulled the fuel cap and whoosh! the entire half a tank ended up down my shirt.Refueled, and again same thing.WTF? figuring I would look at back at the shop, I dropped it in the trailer and fired the 357.Ran fine for the first hour, then after stopping to yack with a nosy neighbor, it also performed the same trick as the 372.Fuel all over the place and refused to start.

Being the common denominator, I dumped the fuel jug this morning and have had no problems all day with fresh fuel, although it was pretty warm today as well.Fuel in the jug wasnt old, less than two weeks old,but still it puzzled me.Saws acted like a vapor lock, after pulling the fuel lines you could plainly hear a hissing sound like pressure was relieved,but I have never had a saw do this before.

Anyone got any ideas what was wrong with this fuel?


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## SDB777 (Apr 25, 2011)

Ethanol?


BTW, describe hot....cause it ain't been that yet for us in the south. Run my Stilh when it's a 105*F with 80% humidity....never had that happen, and that's hot!





Scott B


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## chipherder (Apr 25, 2011)

It'll be interesting to hear what the experts say about this, I was thinking fuel cap vent, but never heard of it shooting fuel out of the tank.


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## avalancher (Apr 25, 2011)

chipherder said:


> It'll be interesting to hear what the experts say about this, I was thinking fuel cap vent, but never heard of it shooting fuel out of the tank.


 
Thats the first thing I thought of when the 372 blew its fuel,vent clogged up.But, seeing as how this saw has less than 2 hours on it, it made me wonder.Being pressed for time, I set it aside and grabbed the 375 and had a repeat performance.

Now today,with a batch of fresh fuel in the jug, I havent had a lick of problems.with either saw.Scratching my head over this one for sure.


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## bobt (Apr 25, 2011)

This was common for the old Homelites like the Xl12, Xl Auto, or Super EZ Auto. They would boil the gas in their tanks. But remember that the gas tanks on these saws were built into the crankcases.

I have a Husky 61 that will also vapor lock when cutting in 90 degree weather. I still can't figure out why I choose to cut firewood in the heat of the summer, but I do.

There isn't really much that anyone can do to avoid it except not cutting in the heat. Just let it cool down, and then you can start them again.

It's hard to imagine that the gas affects this,,,but who knows?

Bob


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## nmurph (Apr 25, 2011)

SDB777 said:


> Ethanol?
> 
> 
> BTW, describe hot....cause it ain't been that yet for us in the south. Run my Stilh when it's a 105*F with 80% humidity....never had that happen, and that's hot!
> ...


 
I was running my saws Sat. It was 94° (I guess summer is still a few weeks away) but the humidity was only about 70%. I noticed they were a little harder to restart.

Usually a tank vent problem will cause a vacuum as the fuel is pulled out. I guess it could be a tank vent problem. When it gets hot my mix jugs will swell (plastic with the accordian style tube that slides back into the can and a lid screws on top) will gush fuel all over you if you open the lid without cracking the vent first.


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## SDB777 (Apr 25, 2011)

I was trying to figure out why the fuel tank built up air pressure...not so much as having a vaccuum in the tank?

Maybe the ethanol in the fuel is boiling during shutdown and building pressure?




Scott B


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## TreePointer (Apr 25, 2011)

I've had fuel boil out of my MS361 as a result of a malfunctioning breather valve. I could hear a sucking sound as the cap was cracked open and then the fuel boiled out of the tank as a result of the relatively low pressure condition inside the tank.

The initial cutting session always went okay, but I couldn't start the saw after taking a short break. What I find eliminates this problem (apart from replacing the tank breather valve) is to crack open the fuel cap immediately after stopping the saw to allow air into the tank, which relieves the low pressure condition.


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## zogger (Apr 25, 2011)

*extra ethanol?*

Is this ethanol gas for the 2 stroke mix? Maybe you got a batch with way more than 10% in it. I've heard of places-rumors on the internets-that will slip a lot extra into a tanker full. (it's only about two bucks a gallon right now, they slip extra in, that's a lotta profit to be made selling at near four bucks or extra change a gallon for ethanol mix pump fuel)

If that ain't it, no idea.


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## thomas72 (Apr 25, 2011)

I am an expert my no means. I have some saws that are just a few years old and some that are decades old. I have had no problem with vapor lock. More often I see people let a hot saw idle for a good duration and then shut the saw down. While at idle some saws will have fuel puddle ever so slightly in the crankcase and when shut down and restarted they may flood. As with the fuel spilling is very common when you tilt the saw ever so slightly and open the tank while under pressure.


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## blue dog (Apr 25, 2011)

zogger said:


> Is this ethanol gas for the 2 stroke mix? Maybe you got a batch with way more than 10% in it. I've heard of places-rumors on the internets-that will slip a lot extra into a tanker full. (it's only about two bucks a gallon right now, they slip extra in, that's a lotta profit to be made selling at near four bucks or extra change a gallon for ethanol mix pump fuel)
> 
> If that ain't it, no idea.


 
my local saw shop has a tester he said he has got as high as 35% in my area


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## zogger (Apr 26, 2011)

*Ha!*



blue dog said:


> my local saw shop has a tester he said he has got as high as 35% in my area



I figured that was going on a lot with gas stations, with ethanol being half price of pure gasoline. I think a high ratio like that in the mix might lead to "boiling" on a hot day.

Personally..I am not so much in disfavor of ethanol fuel IF it is limited to four strokes, all the gaskets and lines and carbs/injectors, etc are designed for it, it isn't made from normal food crops, and/or is home made by the end user. 

(One can go to the BATFE website and download the appropriate permit for legal distillation at home for fuel use, it's really not much of a hassle or expense at all, as opposed to the other things you would use those boys for).

I was actually going to send my application in and do it myself (using spoiled animal feed for the feedstock), but decided I was going to all diesel eventually. My small engine use..I'll pay whatever pump price is for gasoline, and I can still get no ethanol locally.


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## Bob Wright (Apr 26, 2011)

chipherder said:


> It'll be interesting to hear what the experts say about this, I was thinking fuel cap vent, but never heard of it shooting fuel out of the tank.


 
Nope not ethanol. Mine has been doing it for 33 years when it gets hot outside. So much better to cut in the winter as the problem is gone...Bob


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## roanokejim (Apr 26, 2011)

I also think it is not the Ethanol. I am also curious about what it is.


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## jeeptj19992001 (Apr 26, 2011)

blue dog said:


> my local saw shop has a tester he said he has got as high as 35% in my area



well my aunt may's best friends neighbor's barber says bull ship


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## eyolf (Apr 26, 2011)

If you were farther north I might be tempted to blame it on "winter gas". Up here where sometimes the weather gets cool, we get "winter gas"...lighter fractions contained therein to vaporize easily for fast starts at 30 below.

Up here most distributors stop getting it from the refineries in March. WE can tell because winter gas smells different; summer gas has a slightly "sulphur-ry" smell, burns your nose like diesel fuel.

IF you've had the gas for a while...?


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## Bob Wright (Apr 26, 2011)

roanokejim said:


> I also think it is not the Ethanol. I am also curious about what it is.


 
This is my surmize from playing with the magnesium cased Echo's for the last 35 years. The saw is building up heat real quick and the case is soaking it all up like a big heat sink. Now the gas in the tank starts to boil (doesn't matter if the vent is working or not) the thing is hot. Now you open the cap with still boiling fuel and there she blows. Been watching it happen for ever every summer. Now Echo tried to reduce the boiling in the tank by isolation of the tank with the saws with the plastic tanks inside a tank. Like the CS-500, CS-650 and the like. Just my thoughts...Bob


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## nmurph (Apr 26, 2011)

That is plausible. Even if the fuel is not boiling, the heat causes a rise in pressure and the sudden loss of that pressure will cause instant boiling. That is similar to why water will boil on top of Everest at less than 160°F


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## Fred482 (Apr 26, 2011)

I'm getting so skeptical of the fuels from the pump that I dug out my old fuel quality test kit. It was a special service tool, issued by GM back in the early '80's, to the dealership to test fuel quality issues after the oil embargo and such incidents played havoc with performance vehicles. Most of the problems were traced to fuel system design, not the fuel quality.

I used it on some pump gas recently purchased and found exactly 10% etoh. I guess that's good...........?!?! :msp_scared:


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## cat-face timber (Apr 26, 2011)

In my old (recently traded) Poulan Pro 525, the fuel would boil in the tank, it did not affect power or runing of the saw, but when I would open the cap to add more fuel the gas would boil over and get everywhere. I assumed it was the tank vent, which in this saw is the cap itself, I "unplugged" the tank vent and that stopped the boiling.

Hope this helps!


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## avalancher (Apr 26, 2011)

cat-face timber said:


> In my old (recently traded) Poulan Pro 525, the fuel would boil in the tank, it did not affect power or runing of the saw, but when I would open the cap to add more fuel the gas would boil over and get everywhere. I assumed it was the tank vent, which in this saw is the cap itself, I "unplugged" the tank vent and that stopped the boiling.
> 
> Hope this helps!


 
But in this case, I didnt have a vacum going, it was pressure.Even after the cap came off, you could still see air bubbles flowing out of the air filter, BACK INTO THE TANK. That was the part that really weirded me out, pressure built in the tank,not a vacum like what you would see when the vent was plugged off.


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## Al Barnes (Jul 29, 2013)

Chainsaw vapor lock is due to ethanol being a component of the fuel. Solution=ethanol free premium fuel. Found out about this the hard way. Twice I was way back in the mountains @ 7,000 + feet and had both saws, a Stihl and a Jonsered, refuse to restart. Had to leave with only what had been felled and blocked. About 1/2 cord each time. Wasted day.


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## Bob95065 (Jul 29, 2013)

avalancher said:


> I had a unusual occurence this past weekend, at least for me. Guy down the road had a large white oak he wanted down and gone, and I decided to take it down and haul it out on Saturday.It was warm, mid nineties, and i dragged along the 357XP for brush duty and the 372xp for the main stem.
> 
> After a lunch break, the 372 refused to start.It would pop, run a second then quite.Exasperated, i pulled the fuel cap and whoosh! the entire half a tank ended up down my shirt.Refueled, and again same thing.WTF? figuring I would look at back at the shop, I dropped it in the trailer and fired the 357.Ran fine for the first hour, then after stopping to yack with a nosy neighbor, it also performed the same trick as the 372.Fuel all over the place and refused to start.
> 
> ...



Sounds like a bad day to take up smoking with all that fuel on your shirt.


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## nmurph (Jul 30, 2013)

Al Barnes said:


> Chainsaw vapor lock is due to ethanol being a component of the fuel. Solution=ethanol free premium fuel. Found out about this the hard way. Twice I was way back in the mountains @ 7,000 + feet and had both saws, a Stihl and a Jonsered, refuse to restart. Had to leave with only what had been felled and blocked. About 1/2 cord each time. Wasted day.



Well, there you go, it's a fact. 

What you put forth is anectdotal evidence. It doesn't even begin to come close to proof.


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## little possum (Jul 30, 2013)

Had a fella explain a similar situation to me today, but he has a 041. IDK how to fix it, and dont really know that I want too


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