Tuning question?

[dodge man]

I’ve got a Stihl MS261, about 7 years old. It’s had what I’d call moderate use, far from worn out. I’ve never touched or needed to touch the tuning screws until recently. It starts fine and when cold and warming up no problem. If I don’t shut it off I can run a tank of fuel through it. The problem is a warm or hot start. It starts easy enough but it’s very difficult to get it off idle. Even just barely touching the throttle it wants to die. Hit the throttle hard and it does die. If you’re patient enough it will eventually run normal.

I turned the low screw out about a half turn, no help. Rather than randomly turning screws I thought I’d look for ideas. It’s warmer hear, I’ve been using it when the temps are in the 50’s to 70’s.

 

[RayIN]

When hot, the fuel becomes pressurized until it cools. IMO what is happening is this causes the engine to flood when restarted hot. Try loosening the gas cap, then re-tighten before starting to eliminate any pressure in the tank.
Might not be your problem, but costs nothing to try.

 

[dodge man]

When hot, the fuel becomes pressurized until it cools. IMO what is happening is this causes the engine to flood when restarted hot. Try loosening the gas cap, then re-tighten before starting to eliminate any pressure in the tank.
Might not be your problem, but costs nothing to try.

Thank you! The second I read your post I realized that is probably it. I took the cap off to check the fuel level when I was having problems and there was quite a bit of pressure.

 

[xyz123]

Also this time of year if mixed recently could be winter blend of fuel. Known to boil and create pressure in heat.

 

[dodge man]

Well taking the cap off didn’t help. Xyz123 hit it on the head, when I took it back it my shop after using it today the fuel was boiling.

 

[RobertN]

Also this time of year if mixed recently could be winter blend of fuel. Known to boil and create pressure in heat.

Curious how that happens? Lots of alcohol/ethanol with low vapor pressure?

That's something I have not seen personally in the funky Calif Smog gas we get out here.

 

[RobertN]

Other question, if it's boiling shouldn't that vent? Is it possible on that 7 year old saw the tank vent isn't working up to par?

 

[xyz123]

Got me.

A common known problem for many years now with winter blend fuels when it gets warmer.

Switch to a non winter fuel no issues. Switch to Efree no issues. Switch to a canned fuel no issues.

Easy fix. So why try to figure out a problem with winter blend in a chainsaw in warm weather. Just dont do it.

 

[dodge man]

It’s ethanol free but probably is “winter fuel”. I’m not sure this is the correct term but winter gas vaporizes easier for better cold weather starts. Hence it gets hot in the saw and boils.

 

[ericm979]

Stihl has very good instructions on how to tune the carb in most of their owners manuals. Both with a tach and without.

 

[xyz123]

I've never bought Efree in middle of winter to know if they have a winter blend of that. I always stock up in of fall before winter.

Thats interesting if they do since you said your is Efree doing. Sounds like they do it for everything else so would make since.

Info on winter blends by amsoil. The Difference Between Winter- and Summer-Blend Gas - AMSOIL Blog

 

[dodge man]

Stihl has very good instructions on how to tune the carb in most of their owners manuals. Both with a tach and without.

I’m guessing used to have good instructions. I can’t find it anymore in the owners manual. I might just be looking in the wrong place.

 

[xyz123]

@RobertN that article has info in there are your guys Calif gas too.