I have a Stihl 034 AV. Vapor Lock perhaps and Hissing ?

[Johndrew98]

Filled it up with gas and oil. Cold 60 degrees and it started. It was running great (30 minutes)then the chain came off. I could hear a noise sounding like water on a hot stove burner.Hissing. I first thought it was the clutch just spinning but it lasted several minutes. I fixed the chain now it will turn over with force about one piston turn. . (vapor Lock perhaps) I took out the sparkplug and pulled it several times. Pulls easy but the vapor lock returns when I put it back in. Someone said to take a Dremel tool and cut slits in the muffler. Any thoughts.

 

[Maintenance supervisor]

Filled it up with gas and oil. Cold 60 degrees and it started. It was running great (30 minutes)then the chain came off. I could hear a noise sounding like water on a hot stove burner.Hissing. I first thought it was the clutch just spinning but it lasted several minutes. I fixed the chain now it will turn over with force about one piston turn. . (vapor Lock perhaps) I took out the sparkplug and pulled it several times. Pulls easy but the vapor lock returns when I put it back in. Someone said to take a Dremel tool and cut slits in the muffler. Any thoughts.

If fuel mix was blowing out the plug hole or dripping/ running out of the muffler, I'd say vapor lock was possible.
It sounds like something is obstructing the revolution of the motor though?
Check your flywheel and coil for any play or interference, if non then clutch springs and lastly pull the cylinder if no other problems are discovered.

 

[Johndrew98]

I took off the muffler and has the same effect. Has crisp spark. It usually will release the compression after several hours and will start and run like new.[

 

[Johndrew98]

 

[Old2stroke]

Vapor lock is usually a problem confined to the carb due to hot fuel and a hot carb and would be fairly rare to be a condition that would affect the difficulty of turning the saw over. When you stop a hot saw, the fuel in the tank can soak up heat from the saw and expand, exerting more pressure on the inlet valve of the carb and if the pop-off pressure is too low, it can flood the carb, allowing fuel to get into the engine and that might be the hissing sound when fuel hits a hot piston blocking the intake port. This is all strange, as you would think it would cause flooding and the engine would be hard to start but not difficult to pull over unless the crankcase is filled with fuel. Have you tried holding the saw upside down and pulling it over with the plug out to see if fuel sprays out, indicating a flooded condition?

 

[stihltech]

Check the fuel tank vent.