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Fuel boiling

gtsawyer

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I've seen it a few times too - in either/both an MS290 and a 036 (Pretty sure the MS290, likely the 036 too).
 
bryanr2

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We had at least ten members in this thread say they have seen it. I have seen it twice but just in this saw. Mind you it is the only one I have with a metal fuel tank. so is there a fix? is there a concern long term to the saw? etc.
 
Justsaws

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We had at least ten members in this thread say they have seen it. I have seen it twice but just in this saw. Mind you it is the only one I have with a metal fuel tank. so is there a fix? is there a concern long term to the saw? etc.

2094/5s were fairly well known to do what you are describing. The early 2094s were the worst at it.

If the saw is in good shape, clean of excess debris, fuel system in good working order, the next best thing is to keep the saw in operating on the high side of its rpms, bogging it down will make it worse. It can happen if you start the saws and leave them sit on the ground at idle on a warm day. Play attention to the saw because it can cause problems such as flooding or at the extreme pissing pre-heated gas all over the place. The tank vent system can fill with fuel which can lead to a lean condition.

Fuel quality makes a difference as well.

I really like my 2094/5s but there are reasons why the Husqvarna group went with the isolated fuel tank design, it simply works better.

In terms of an easy fix, I have been told everything from a different heat range sparkplug, run it richer, to muffler mods, and no those suggestions did not "fix" it.
 
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pdqdl

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I've never seen it happen. It sounds particularly dangerous if it is boiling over when you uncap it.

If your saw is running that hot, I would suspect air flow obstruction, reflected/diverted muffler heat, or really poor design.

Nobody has mentioned the heat radiated by a hot clutch. If you are running wide open and you stall the saw very often, you will be converting engine horsepower directly into heat in the clutch. This might allow enough radiated heat to boil the gas, particularly if there are other problems as well.

Altitude will always be a factor in lowering the boiling point of any fluid; definitely a consideration if you are very high up.

Ethanol will not lower the boiling point, it will raise it; ethanol content is not likely to be a cause.
 
pioneerguy600

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Fuel boiling in the tank is nothing new at all, the older saws simply vented into the atmosphere and it was not an issue with them. When the manufacturers were forced to start using sealed fuel tanks then a newer design of vent prevented the fuel vapor from escaping into the atmosphere, the fuel tanks were still metal and often just a part of the saw, they were not separated and this caused some fuel delivery problems. Manufacturers went to the separate fuel tank designs, most started using plastic tanks and this helped a lot but on hot days with the engine contributing additional heat the fuel still boils, the tanks are now all sealed with the vent only allowing air to enter a tank, no fuel or vapor to escape into the atmosphere. Tanks will pressurize easily, the carbs are designed to work with this pressure and there is nothing that will really stop this. It has already been mentioned about the different gasoline mixtures supplied by the refineries for winter, its been noted that some mixes boil more easily and that certain grades will be a little more resistant to boiling than others. I have used all grades supplied for my area and they all boil when the temp rises, there really is nothing that can be done to stop this with regular pump gasoline. When the tank pressurizes the fuel is actually force fed to the carb , the spring under the metering lever is designed with a pop off pressure that prevents too much fuel from entering the fuel bowl part of the carb and flooding out the engine so the engine will run normally with the fuel boiling in the tank. By leaving the tank cap on the fuel will boil less as the pressure inside the tank rises but care must be taken when removing the cap as the sudden release of the built up pressure will cause spraying of fuel mix.
 
bryanr2

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Fuel boiling in the tank is nothing new at all, the older saws simply vented into the atmosphere and it was not an issue with them. When the manufacturers were forced to start using sealed fuel tanks then a newer design of vent prevented the fuel vapor from escaping into the atmosphere, the fuel tanks were still metal and often just a part of the saw, they were not separated and this caused some fuel delivery problems. Manufacturers went to the separate fuel tank designs, most started using plastic tanks and this helped a lot but on hot days with the engine contributing additional heat the fuel still boils, the tanks are now all sealed with the vent only allowing air to enter a tank, no fuel or vapor to escape into the atmosphere. Tanks will pressurize easily, the carbs are designed to work with this pressure and there is nothing that will really stop this. It has already been mentioned about the different gasoline mixtures supplied by the refineries for winter, its been noted that some mixes boil more easily and that certain grades will be a little more resistant to boiling than others. I have used all grades supplied for my area and they all boil when the temp rises, there really is nothing that can be done to stop this with regular pump gasoline. When the tank pressurizes the fuel is actually force fed to the carb , the spring under the metering lever is designed with a pop off pressure that prevents too much fuel from entering the fuel bowl part of the carb and flooding out the engine so the engine will run normally with the fuel boiling in the tank. By leaving the tank cap on the fuel will boil less as the pressure inside the tank rises but care must be taken when removing the cap as the sudden release of the built up pressure will cause spraying of fuel mix.

Jerry,
so on these older saws, it is to be expected? and it just goes with the design? I postd some pics in my second post that show a little fuel dribbling under the clutch cover, is this the saw's attempt to regulate the boiling and keep te saw from flooding?
thanks
 
Justsaws

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Jerry,
so on these older saws, it is to be expected? and it just goes with the design? I postd some pics in my second post that show a little fuel dribbling under the clutch cover, is this the saw's attempt to regulate the boiling and keep te saw from flooding?
thanks

PG600 pretty much nailed it. It is to be expected. It does go with the design. Not positive but I am thinking that where you see the fuel dripping from is under where the fuel tank vent terminates into the vent system tower. The vent system gets fuel in it and can pull the fuel back into the tank, it will also purge fuel. As long as the system is functioning properly you should be fine.

It is really only an issue when something is not working correctly, such as the carb kit is bad and the saw floods out because the metering side failed or the fuel line shrink and the saw starts pissing gas all over when on its side.

There are two cylinder gaskets on 2095s a thin typical gasket and a thick heat isolating gasket. The last time I ordered the thick gaskets they were alum crush type material and that is what I see most often on the 2095s. If by chance your saw is missing the thick gasket that can make it worse, just keep an eye on it. Usually the piston would hit the top of the cylinder without the thick gasket but somebody may have been into it.

Remove fuel cap slowly, tank under pressure.

Do not let a little fuel dampen the mood, but be wary of a lot of fuel.
 
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rbmopar

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The partner 500/5000 family of saws will easily boil fuel as well. Had a 500 that was building enough pressure to overcome the needle and seat yesterday. The saw would suddenly flood out and die in the middle of a cut. Loosen the fuel cap and let things cool off and away you would go for a while. It was 95 out, and I was cutting largish wood. A new carb kit would probobly prevent this, but it works fine under normal conditions. Don't let it bother you, nature of the beast.
 
bryanr2

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Thanks for all your replys. I kinda thought it was power for the course.... as per design, but was not sure. That's why I brought the question here. Having read thousands of threads, I've learned who I can trust for help. Thankfully, some of the individuals showed up in this thread and provided us with good information that we can all reflect on and review if this ever arises with one of our own saws. I sincerely thank each of you for your contributions to this thread.

Regards,
 
pioneerguy600

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Jerry,
so on these older saws, it is to be expected? and it just goes with the design? I postd some pics in my second post that show a little fuel dribbling under the clutch cover, is this the saw's attempt to regulate the boiling and keep te saw from flooding?
thanks

Yes, all saws including the latest designs still have fuel boiling and pressurizing the fuel tank, a proper working tank vent on these saws will not allow any leakage to the outside atmosphere. If the design was of an older saw then some had vents that would limit the leakage from the tank via a tube/line usually with a grub screw or two inside the line or various other devises that restricted fuel from escaping. However these type of vents did leak a little and that is what you are likely seeing dripping out from under your saw when the temp is up and the tank is pressurised. It is not really your saws attempt to regulate the boiling, they are not designed to do that as such and if your carb is working correctly it will be able to deal with the extra pressure you are seeing from the fuel expanding/ vaporizing in the tank. There is a small spring in the carb, under the metering lever that is a very specific spring designed to work with that model and number of carb. It is designed for a specific pop off pressure, most are set around 10-12 psi. That is a lot of pressure, the small coil spring can hold back that pressure easily until the pressure is exceeded and that seldom happens. If it did then your carb would flood out and stall the engine. If a saw is experiencing flooding out under these conditions the carb needs to be rebuilt and a new specified spring with the proper pop off resistance installed.
 
ptjeep

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My homelite xl-925 did it last summer while noodling some red oak. The first run of Yamaha Grizzly 700's will do it also. I found a different tank vent on a atv forum that fixed the grizzly but i'm guessing theres no fix for these older saws. Its kinda freaky to take a gas cap off and have gasoline shoot up like a geyser!
 
powerking

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so my buddy is going through this on his XL-925 now, it runs great...until you shut it off, then open the cap and see the boiling and saw will not restart until cooled...
 
anlrolfe

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My FIL gave me an old Homelite many moons ago. It was a POS that had been thrashed, run hard and put up wet. It had been worked like a rented mule well before I got it.
The bottom of the case had been JB-Welded to fix some big cracks. I suspect it had either been dropped out of a tree or a tree dropped on it.
At the time I was happy to get a few cuts out of it for landscape maintenance around the house. It would boil the gas in the blink of an eye then vapor lock. I suspected it had major alignment/bearing issues inside or air leaks causing the problems. I got tired of messing around with it and happily chucked it one day. I replaced it with my little Echo CS-306.
 
fossil

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The $109.00 pm700 arrived today. Its very oily grimy. The fuel tank is missing the 2 bolts to hold it on. One at rear carb and in oil tank. The 2 bolts under the carb were loose. The coil was very loose rubbing the flywheel. Has the wrong spark plug in it. But, it has great compression and no scoring on the piston or cylinder!! I can replace bolts. The clutch cover though broken at muffler is usable. I have one off of a sp81 i can use if it makes it look better. But i think ill have a great runner once i clean it and put it back together. Ill post once its clean and running. Jethro, its got a sdc 44a carb on it.

so my buddy is going through this on his XL-925 now, it runs great...until you shut it off, then open the cap and see the boiling and saw will not restart until cooled...

A couple of things that make those boil fuel. Make sure the duckbill valve in the fuel cap is working. Most turn to goo over time. It's under the sintered plug in the side of the fuel cap. Pry it out with an awl or small screwdriver and clean the plug and valve well out.

Homelite PN 69451 Stens still makes them. It will raise pressure in the tank and increase the boiling point of the fuel.

The pic is big, the valve is very small.

316GhOkt1rL._SX425_.jpg


The other thing to watch for is saw cake piled up between the fuel tank and the crankcase. Blow that out and keep it clean to prevent heat transfer from the crankcase.
 
catbuster

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Stihl had to recall a bunch of 461s because fuel was hot, boiled & sprayed out on them, and sometimes lit off. For a while I had to tell my guys to let the 461 crew saws cool off before they refueled. Some 441s, 440s & 460s had this issue, and it was due to tank vents.

Here’s a link to the recall annoucement on WildfireToday:
https://wildfiretoday.com/2017/02/23/stihl-recalls-100000-chain-saws/

And the story about a guy getting burned:
https://wildfiretoday.com/2016/11/04/another-firefighter-burned-by-chain-saw-fuel-geyser/
 
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