Chain spins at idle when low on gas

[Amin_1992]

Hey guys. Never saw this phenomenon before!

I was running my MS261 bucking wood, when I noticed that after cutting a lot, idling, the chain was still spinning at a good speed! Never did that before. I grabbed my kit and was beginning to adjust her, when she died. I then realized I was out of fuel ha.

Anyway, refueled, and now the idle was back to normal. No chain spin at idle.

Curious if that is "normal" when low on fuel? My only thought was is that I was running extra lean since the gas was about out, and that caused the inbalance in fuel/air, running lean and increasing idle speed a bit.

What do you think? Ever see that before?

 

[Marley5]

The increase in idle is how I know my saw is about to run out of fuel.

 

[Amin_1992]

The increase in idle is how I know my saw is about to run out of fuel.

Ha! In 7 years of using a chainsaw steadily I never noticed that little trick. Thanks!

 

[lone wolf]

Hey guys. Never saw this phenomenon before!

I was running my MS261 bucking wood, when I noticed that after cutting a lot, idling, the chain was still spinning at a good speed! Never did that before. I grabbed my kit and was beginning to adjust her, when she died. I then realized I was out of fuel ha.

Anyway, refueled, and now the idle was back to normal. No chain spin at idle.

Curious if that is "normal" when low on fuel? My only thought was is that I was running extra lean since the gas was about out, and that caused the inbalance in fuel/air, running lean and increasing idle speed a bit.

What do you think? Ever see that before?

Can you check the idle speed with a tach?
Also look and see if one of the clutch springs are broken.

 

[Amin_1992]

Can you check the idle speed with a tach?
Also look and see if one of the clutch springs are broken.

I could yes but I could audbily hear it was running faster with an empty tank, then returned to a normal sound after refueling.

 

[Woodtroll]

My only thought was is that I was running extra lean since the gas was about out, and that caused the inbalance in fuel/air, running lean and increasing idle speed a bit.

Yes, I think you're exactly right. I try to cut my saws off as soon as they do this, to save them from running completely dry. That way I don't have to add extra pulls to prime it again after refueling. I'm lazy that way.

 

[Old2stroke]

Normal. As a saw runs out of fuel, it starts to run lean and that’s what makes it speed up

 

[lone wolf]

I could yes but I could audbily hear it was running faster with an empty tank, then returned to a normal sound after refueling.

So what is your idle speed on that saw? Is it an Mtronic ?

 

[Amin_1992]

So what is your idle speed on that saw? Is it an Mtronic ?

I don't remember off the top of my head, would have to measure and read the specs. But i bought it new 2 years ago and it idled perfectly and to spec.

Nope no m tronic, I fought long and hard to find an old school carb 261!

 

[buzz sawyer]

When I prep my saws for long-term storage, I let them idle until they run out of fuel. The speed may increase briefly right before they run out. I try to not let them run low while I'm cutting.

 

[singinwoodwackr]

Might as well pull the clutch drum and clean it

 

[Pioneer]

What's happening is the saw runs at optimum F/A ratio just before it lean dies. We have to set up our saws slightly rich at idle so they don't lean stall during a cold start before they get a chance to warm up. When they are warm they are running a little too rich and it slows the idle down. Fuel starvation changes the tune toward lean and finally the fire goes out.

 

[mowmow]

I told the police officer that exact same thing - he still gave me a speeding ticket.

 

[HankinOhio]

Normal. As a saw runs out of fuel, it starts to run lean and that’s what makes it speed up

Most naturally aspirated engines do this. I try not to let this happen in 2 strokes as the condition acts as if there is too little oil in your fuel mix wearing piston and cylinder each time it happens.

 

[Amin_1992]

That makes sense to me. It honestly just snuck up on me. Usually I'm topping off the tank so I guess I got distracted - as I said, I started tuning the carb before I thought to even check the fuel level ha! Time flies when youre having fun

Thanks all

 

[dboyd351]

If you run your carbureted saws dry to store them you will see this happen whenever they are about to run out of fuel.
It is normal.

 

[Fordiesel69]

Hey guys. Never saw this phenomenon before!

I was running my MS261 bucking wood, when I noticed that after cutting a lot, idling, the chain was still spinning at a good speed! Never did that before. I grabbed my kit and was beginning to adjust her, when she died. I then realized I was out of fuel ha.

Anyway, refueled, and now the idle was back to normal. No chain spin at idle.

Curious if that is "normal" when low on fuel? My only thought was is that I was running extra lean since the gas was about out, and that caused the inbalance in fuel/air, running lean and increasing idle speed a bit.

What do you think? Ever see that before?

Yes indeed normal. My trimmers, blowers, and saws all do this. If they don;t then you know the fuel filter has come off. The filter allows some bubbled fuel to flow for just a short bit before total fuel exhaustion.