1. A 'classic' 2-stroke engine has the carb feeding into the crankcase,
where the fuel/oil mix lubes the bearings. What happens to that fuel?
It seems it must end up getting burned? If so, does it need to
re-vaporize?

2. Our Stihl trimmer (FS36) has a membrane carburator. AIUI, these are
supposed to operate in any position. So, what drives the fuel from the
tank to the carb? I'd thought that the fuel tank was (slightly)
pressurized for this. (There's a 2nd hose between them, running through
the primer bulb.) But, when I remove the carb fuel hose, with the
engine running, no gas comes out of the hose. Is fuel just pulled by
the venturi vacuum?

Thanks,
George

On 5/20/2011 9:45 AM, George wrote:
1. A 'classic' 2-stroke engine has the carb feeding into the crankcase,
where the fuel/oil mix lubes the bearings. What happens to that fuel?
It seems it must end up getting burned? If so, does it need to
re-vaporize?

2. Our Stihl trimmer (FS36) has a membrane carburator. AIUI, these are
supposed to operate in any position. So, what drives the fuel from the
tank to the carb? I'd thought that the fuel tank was (slightly)
pressurized for this. (There's a 2nd hose between them, running through
the primer bulb.) But, when I remove the carb fuel hose, with the
engine running, no gas comes out of the hose. Is fuel just pulled by
the venturi vacuum?

Thanks,
George


1. the fuel/oil mix is transferred to the cylinder and burned

2. The diaphragm in the carb IS the fuel pump. There are two little
check valves as a part of the assembly, and the motion of the diaphragm
along with the needle and seat cause fuel movement. The diaphragm is
driven by crankcase pulsations via a small hole you will see next to the
main port. In the case of some chain saws with isolated carbs, you will
see a "pulse" hose connecting the crankcase to the carb.

--
Steve Barker
remove the "not" from my address to email

On May 20, 10:45*am, George wrote:
1. A 'classic' 2-stroke engine has the carb feeding into the crankcase,
where the fuel/oil mix lubes the bearings. *What happens to that fuel?
It seems it must end up getting burned? *If so, does it need to
re-vaporize?

2. Our Stihl trimmer (FS36) has a membrane carburator. *AIUI, these are
supposed to operate in any position. *So, what drives the fuel from the
tank to the carb? *I'd thought that the fuel tank was (slightly)
pressurized for this. *(There's a 2nd hose between them, running through
the primer bulb.) *But, when I remove the carb fuel hose, with the
engine running, no gas comes out of the hose. *Is fuel just pulled by
the venturi vacuum?

Thanks,
George

The gas/oil mixture is sucked in thru the carb when the piston goes
from bottom to top. When the piston is coming down, it forces the gas/
oil thru a port in the cyclinder walls and into the combustion chamber
and then the spark plug ignites it. For more info, google it.

Removing a fuel line while the engine is running is asking for
disaster. If fuel got on the spark plug, muffler or close to any
ignition source, you'll have a fire. You were lucky fuel didn't run
out, get on you and ignite.

Hank

On May 20, 4:54*pm, Hank wrote:
On May 20, 10:45*am, George wrote:

1. A 'classic' 2-stroke engine has the carb feeding into the crankcase,
where the fuel/oil mix lubes the bearings. *What happens to that fuel?
It seems it must end up getting burned? *If so, does it need to
re-vaporize?

2. Our Stihl trimmer (FS36) has a membrane carburator. *AIUI, these are
supposed to operate in any position. *So, what drives the fuel from the
tank to the carb? *I'd thought that the fuel tank was (slightly)
pressurized for this. *(There's a 2nd hose between them, running through
the primer bulb.) *But, when I remove the carb fuel hose, with the
engine running, no gas comes out of the hose. *Is fuel just pulled by
the venturi vacuum?

Thanks,
George

The gas/oil mixture is sucked in thru the carb when the piston goes
from bottom to top. When the piston is coming down, it forces the gas/
oil thru a port in the cyclinder walls and into the combustion chamber
and then the spark plug ignites it. For more info, google it.

Removing a fuel line while the engine is running is asking for
disaster. If fuel got on the spark plug, muffler or close to any
ignition source, you'll have a fire. You were lucky fuel didn't run
out, get on you and ignite.

Hank

There is a transfer port between the cranckcase and the cylinder. It
goes into the cylinder opposite the exhaust port.
When the piston descends, the air gas mixture is transferred to the
cylinder.