I had three saws that would not run yesterday after refilling the fuel tanks. I am wondering if I got bad gas. How would I tell if so? How would I prove bad gas? And I am looking for advice. Any way to test the gas?
Saws are Stihl, MS 261 CM, MS 400 CM, and a MS 500i with a manufacturer recommendation of running 50:1 fuel mix.
I would like to be thorough and explain all events leading up to my three saws quit running. This will be long winded but I want all the information given to you so I can get good replies that are helpful because maybe I am over looking something on my part and will be obvious to others.
I use non ethanol 91 octane gas for my saw. Only one station in town sells premium ethanol free fuel. I wanted fresh gas before cutting my firewood for the year.
On Friday 03/01/2024, I go by the gas station that sells the premium 91 octane ethanol free fuel to buy gas for my small engines.
They have a dedicated line/hose for the non ethanol gas but I still pump one gallon into my vehicle since they sell both 87 and 91 octane of non ethanol gas and I want to make sure I’m getting gas pumped from the 91 tank into my gas cans. Basically clear out the “old” gas from the hose. Vehicle tank is 75% full and I pumped in one gallon of fuel.
I have a 5 gallon gas tank and I add red armor 2 cycle oil into the gas can. 3.2 oz of oil per gallon of gas. I measured three “servings” of the proper oil amounts from the 16 oz container and pour it into the gas can. Total oil amount was the 9.4 ozs. I am very cautious as to mix the appropriate amount of oil to the gas can. I add 3.1 gallons of gas (pump reads 4.1 gallons because I added the one gallon to my jeep). With the fuel and amount of oil I added this should give me right at a 40:1 mix.
Next I have a VP racing fuel can that holds 6 gallons. I put close to 6 gallons of fuel into this can per the reading on the fuel pump. This leaves quite a bit extra room at the top with air which I am fine with because I don’t want any spills in my jeep.
I noticed the gas cans seemed “low” after “filling them” I had 3.1 gallons in a 5 gallon fuel can (only used for mixed gas and this was empty when I put the fresh gas in it). So common sense, I would think it would be over 1/2 full. I know the gas can can hold more more than it’s listed because manufacturers leave room for air. But this was less than half full. Then the VP fuel can has markings on the plastic with graduates gallon markers. This was showing a hair over 5 gallons and I almost put 6 gallons in it per the gas pump. So this did raise an eyebrow but then again I questioned how accurate these markings are on the fuels cans. No way to be sure if I received the correct amount of gas but I figured the gas station pump is calibrated and is dispensing the correct amount of gas and the plastic fuel container reading on the side isn’t accurate so I pretty much blew it off. Those plastic containers do swell a little in the summer so I told myself the reading on the cans probably aren’t accurate.
So now Sunday I go to cut wood. The three saws have gas in them from the last time I used them. The fuel level in the tanks are ranging from 3/4+ of a tank to 1/2 full so I top all three off with the new gas. They run fine. No problems.
The 261 runs out of fuel first and I refuel. I only have mixed fuel on site and I am very cautious not to straight gas the chainsaws. I personally am the one to fuel the saws. The 261 gets a full tank of new fuel, and I top off the other 2. The 400 gets about half tank of fresh fuel (it originally had the most full tank to begin with, so it received the least of the new/fresh fuel on the first fill before starting). The 500 was about 3/4 empty so I topped it off again with the fresh fuel.
I start the 261 and a buddy is cutting with it. I’m taking a break and I noticed after a few minutes, it starts running rough and dies. He restarts it and it will barely stay running. He says something and I say something about the large temperature change throughout the day. It’s now 80 degrees outside and maybe the m tronic needs to be recalibrated. I recalibrate it and the saw is running better but not great. It runs for another few minutes for him to make made 5 cuts or so but isn’t running great. So I say let’s dump the fuel and re fill it since the first thing in my mind is maybe some saw dust got in the tank. I checked and tank was clean. I noticed when I opened the fuel cap on the chainsaw it was under a vacuum and I could hear the air sucking into the gas tank as I went to open it. The fuel was bubbling from the fuel filter. I dumped the fuel from the tank even though the inside of the tank was clean and I refilled the 261. The saw started and idled for 2-3 seconds then would die. If I tried to blip the throttle the saw died instantly.
I set the 261 to the side and tell him to use the 400 and I’ll see what’s wrong with the 261 when I get back home. He starts the 400 and begins cutting. I proceeded to start the 500i now that it’s been refueled and it will start and idle for about 1 second then die. I try several times With the same results. I can’t try the throttle because it dies too quickly. I started the saw 7-8 times, it would idle for just a second and die. So the 9th is so time after trying to start it, the 500 would not even start.
He noticed me having problems with the 500 and shuts off the 400 and says he doesn’t think the 400 is running like it did before re fueling.
We come to the conclusion that the only common denominator between the three saws is the gas. We go to the local ace hardware and buy a gallon of canned fuel. They only carried tru fuel. I bought one can of tru fuel 50:1 mix. Once back on site, I emptied the tanks of the gas out of all three saws and added the tru fuel to the tanks.
All three saws started with just a few pulls. All three saws ran just fine after that and didn’t have any other problems.
I still have the gas from the gas station, both the mixed gas and the regular gas. I kept it in case it damaged my saws or needs testing.
The vehicle ran fine with no issues but that one gallon was mixed with 15+ gallons of gas that was already in the tank.
I was concerned when I got home about the gas damaging the cylinder or piston on the saws. I pulled the mufflers on the 261 and 400. Looking through the exhaust port, the front of the piston looks great with no marks. I lowered the piston and was looking at the back cylinder wall and I think I see something. It looks the same on both saws. The cylinder is shinny in a few spots on the back and I *might* be able to see two vertices lines. I was reading on here about bad gas damaging the back of the cylinder and piston on the intake side. I was looking at the technical bulletins from stihl and echo diagnosing damaged pistons and these lines on my saws look nothing like the scoring on those pictures. It’s hard for me to tell if I have damage or just normal wear and I can’t get a decent picture with my phone and lighting.
Does this sound like bad gas? If it damaged the saws, would they even be running? I don’t has a compression tester but the saws did seem to run fine after using the tru fuel. No, these saws were not straight gassed.
Another thought I had was if I was “shorted” on the gas and I was mixing it at 40:1 to gain extra lubrication and the manufacturer only recommends a 50:1 mix, and I received less gas than what was shown to be dispensed then could there have been too much oil for the saws to run?
I might be over thinking this and concerned over nothing but if the gas station sold bad gas and damaged my saws, I would want them repaired. Would it be obvious if the saws were damaged and would I be able to see this damage through the exhaust port? Or would the saws need to be taken apart? Any advice would certainly be appreciated.
Edited to add: I noticed the gas bubbling in the chainsaw fuel tank. The bubbles were coming from the fuel filter in the tank. Not sure if the tank was pressurized or under vacuum but I could hear the hiss of air when popping the fuel cap on the chainsaw.
