Chainsaw on the fritz, any Thoughts

[Bob Bouis]

Stihl 2-cycle oil has fuel stabilizers in it already. A lot of them do. But even then the gas is only good for a year or so. Two tops before it starts to gunk up your carb. So if you store your saw for more than a season you should always pour the old gas out and start with fresh.

[Richard Dooling]

I also use TruFuel premix. I've been running a Stihl string trimmer on it for five years and no trouble. No ethanol. As a precaution I do use gas treatment in ethanol engines..

It's not cheap but I run both the trimmer and a chainsaw on TruFuel. So maybe depends on how much fuel you use in a month. No one in my area sells ethanol-free gas (not even marinas!). Well airports do but they won't deal in small quantities. Also I'm not sure how precise the fuel/oil ratio needs to be so I'm leery of me mixing small amounts with precision.

Just using new fuel may not help help any existing conditions but it may avoid future problems.

A note:
Ethanol seems okay in newer engines as long as the engine get very regular use. I had a Yamaha 100 the would run great right out of the mechanics shop ($$$$$) and as long as I ran it regularly. But let it sit for a while and the #4 carb would get sticky. This was despite religiously running it dry and draining the carbs after use. Sold it to someone who uses it at least a couple of times a week and no problem. I bought a small marine EFI.

[Mark Greenbaum]

My friends always say to run the saw out of gas, or drain it when done cutting to prevent gumming. I was going to suggest the diaphragm on the carburetor, or replace the fuel line and inline tank filter. HD sells a kit for about $10, and it worked on my weedeater. Also check that the chain is free to spin - sometimes a clinched chain on the rails can make the load bog it down.

[Bob Bergstrom]

I rebuilt a Stihl carb for a friend who was given the saw that sat for over a year. The inlet was closed with dried ethanol, had to use a drill bit turned by hand to clear it out. Ethanol leaked out the carb gasket, and both were almost like super glue. The fuel line was cracked. The inlet hose leaked, and the diagram in carb was warp and not working. All these problems were described on YouTube with how to diagnose them and procedures to follow.

[Brent Wells]

I also use Trufuel for my saw and weed eater. The 93 octane and no ethanol makes it start first pull every time. Like mentioned it has a 2 year self life when opened and a 5 year unopened. Small carbs do not like ethanol above 10% and I know stihl booklets will tell you to run at least 89 octane which will get you under 9%. If you mix your own gas they also seem to like the synthetic oil mix. Sea foam is one of the best carb/jet cleaners I have found but you may need to tear apart if fuel has started to shellac. Good luck.

[Dom Garafalo]

I've had the same symptoms with both my Stihl chain saw and Echo grass trimmer and it turned out to be a clogged spark arrester.

There's a good chance that's your problem. It is a simple fix. Take off the muffler, which will expose the spark arrester which is simply a small metal screen with very small openings which become filled with carbon. You can either toss the spark arrester or clean the screen and put it back in.

You should check to see if you have a clogged spark arrester before spending any money on other parts or small engine service. This problem is well known with shops that fix and service small 2 cycle engines.

Good luck

Dom

[Todd Mason-Darnell]

Since you can get it started, you try spray some carb cleaner into the air intake (with no filter on) will it is idling.\:

https://www.amazon.com/Gumout-800002...+cleaner+spray

(you can get this at any auto parts store)

If you have a problem with varnish build up, this may help.

[Tom M King]

My first guess would be the spark arrester screen. Been running the Stihl oil in orange bottles?

The spark arrester screen is right inside the exit hole in the muffler. It's held in with one screw. Take that screw out, and slide the little screen out. If you can't see through it very well when held up to the light because of black gunk, that's your problem.

To clean it, hold it with some junk needle nose pliers, and heat it to red hot with a propane torch. Let it cool, and wearing an old glove, use you fingers sliding back and forth over it to release all the ash. It should now be clear like a new screen.

Put it back in, and it should run like a new one.

The orange bottle dino oil is terrible for clogging these screens. I haven't had this trouble since switching all my small equipment to the synthetic oil in silver bottles.

[Scott DelPorte]

If you ruled out the air filter, I would try the mechanic in a bottle before tearing it down. I have had good luck with it bringing back gummed up 2 stroke engines in chainsaws, leaf blowers, line trimmers, etc. that had deposits from gas with ethanol. Follow the directions on the bottle.

I switched to stabilized ethanol free gas and haven't had problems. It is much more expensive but since I use these tools infrequently it is worth it to me.

[Wes Ramsey]

Sounds like either a blocked venturi from varnish or trash that got past the filter or just bad gas.

In my experience a varnished carb isn't easily cleaned without using something designed for the task. Carb cleaner won't even soften it. I buy rebuild kits online ($10-20) and soak all parts of the disassembled carb for an hour or so in a gallon bucket of Chem-Dip I got from the parts store. Rinse in water, blow dry with compressed air, reassemble with new parts and it should run like new. I've even gotten away with reusing all the gaskets before when they're still in good condition.

As far as ethanol gas, it is okay to use in 2-cycle engines. It got a bad rap with small engine owners because seals and other non-metal parts weren't designed to be in frequent contact with alcohol and they would turn brittle and fail. Regardless, it is highly hygroscopic and has a shelf life of about a month without additives. After a month or so the ethanol will have absorbed about as much ambient moisture as it can hold and will start to separate. Additives will help it last longer, but I don't know how much longer it will keep the gas 'fresh'. I've heard Seafoam recommended enough by mechanics and friends that it is all I use. That said, I avoid ethanol when I'm able to.

I've had the same symptoms as the OP in all my 2-cycle engines using old gas. If it is bad enough it won't burn you can pour some in a quart jar and let it sit for a few. You can watch the water settle to the bottom as it separates. Usually it will have a milky look to it.

[Dom Garafalo]

Brian, do yourself a favor, and check for a plugged spark arrester screen before you chase your tail.

I may be wrong, but I believe there's a 50%+ chance your problem is a plugged spark arrester screen.

Keep in mind, if it had bad gas it wouldn't start or idle.

Dom

[Jim Bell]

My first guess would be the spark arrester screen. Been running the Stihl oil in orange bottles?

The spark arrester screen is right inside the exit hole in the muffler. It's held in with one screw. Take that screw out, and slide the little screen out. If you can't see through it very well when held up to the light because of black gunk, that's your problem.

To clean it, hold it with some junk needle nose pliers, and heat it to red hot with a propane torch. Let it cool, and wearing an old glove, use you fingers sliding back and forth over it to release all the ash. It should now be clear like a new screen.

Put it back in, and it should run like a new one.

The orange bottle dino oil is terrible for clogging these screens. I haven't had this trouble since switching all my small equipment to the synthetic oil in silver bottles.

I've had the same symptoms with both my Stihl chain saw and Echo grass trimmer and it turned out to be a clogged spark arrester.

There's a good chance that's your problem. It is a simple fix. Take off the muffler, which will expose the spark arrester which is simply a small metal screen with very small openings which become filled with carbon. You can either toss the spark arrester or clean the screen and put it back in.

You should check to see if you have a clogged spark arrester before spending any money on other parts or small engine service. This problem is well known with shops that fix and service small 2 cycle engines.

Good luck

Dom

I'd check there first.