What's on your bench today?

[Eddy_t]

I thought the point of the tank breather was to stop pressure or vacuum so the tank is at atmospheric pressure. Isn't it the diaphragm in the carb that does the pumping by means of crankcase pressure sucking the fuel through from the tank and into the crankcase ? More likely it means the pipe is blocked.

 

The breather allows air IN, it prevents a vacuum forming, but it does allow pressure to form in the tank, which would push fuel through the lines

 

 

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[GardenKit]

Breathers come in different forms, some of the early ones were little more than restrictions in a pipe which allowed pressures to equalise but stopped fuel sloshing out. They worked both ways.

 

Modern ones tend to work only one way and prevent fuel escaping whilst allowing air in to equalise the pressure inside the tank with atmospheric pressure thereby relieving the vacuum caused by the depleting fuel quantity.

 

Most machines do not pressurise the tank, and indeed do not need to, as atmospheric pressure is sufficient to push fuel up the pickup hose to fill the vacuum caused in the fuel pump chamber by the pump diaphragm.

 

They do however pressurise to an extent by the vaporisation of the fuel as it gets shaken about and warmed up. it is this pressure that pushes the fuel out of loose pipes etc whilst servicing. This apparent pressurisation is not required to enable the engine to run.

[Rich2484]

Breathers come in different forms, some of the early ones were little more than restrictions in a pipe which allowed pressures to equalise but stopped fuel sloshing out. They worked both ways.

 

Modern ones tend to work only one way and prevent fuel escaping whilst allowing air in to equalise the pressure inside the tank with atmospheric pressure thereby relieving the vacuum caused by the depleting fuel quantity.

 

Most machines do not pressurise the tank, and indeed do not need to, as atmospheric pressure is sufficient to push fuel up the pickup hose to fill the vacuum caused in the fuel pump chamber by the pump diaphragm.

 

They do however pressurise to an extent by the vaporisation of the fuel as it gets shaken about and warmed up. it is this pressure that pushes the fuel out of loose pipes etc whilst servicing. This apparent pressurisation is not required to enable the engine to run.

 

Thanks Barrie. It's just annoying me is all so thinking out loud. Saw will start but not rev up or it does for a few seconds then dies out, but restarts first pull. It does adjust on the screws so it's leading me away from air leak, it's dans aspen one and it's my first time playing with aspen.

 

Vac and pressure test tomoz.

 

Oh and it also ran fine until I put the bar and chain on, then it started playing up. So will remove bar and see what happens tomoz. Have to to pressure test anyway.

[GardenKit]

Aspen does not 'gas off' like petrol due to the lack of solvents, so it will not build up gas pressure in the tank. And, as gas pressure is not needed, this is a good thing as there is also less chance of vapour lock in pipes.

 

Your problem sounds like a fuel supply issue though, you have not by any chance got a pinched hose have you?

[Rich2484]

Aspen does not 'gas off' like petrol due to the lack of solvents, so it will not build up gas pressure in the tank. And, as gas pressure is not needed, this is a good thing as there is also less chance of vapour lock in pipes.

 

Your problem sounds like a fuel supply issue though, you have not by any chance got a pinched hose have you?

 

No. Pipes are all good, so is impulse. No splits or kinks. Pipes are all clear, and meter arm is all good.

 

One question I do have is with the walbro and zama tools. It's a walbro carb, but the numbers on it don't match the tool. It's something like wze but the tools doesn't have that number.... It's the right carb. Just can't find the right side of the tool for it.

 

Oh and thanks for clearing up why the hose doesn't have any fuel pressure in it. Like I said first outing with an aspen run saw. So I'm learning.

Edited January 2, 2014 by Rich2484

[peatff]

Thank you GK, glad I wasn't labouring under a misapprehension all this time.

[GardenKit]

One question I do have is with the walbro and zama tools. It's a walbro carb, but the numbers on it don't match the tool. It's something like wze but the tools doesn't have that number.... It's the right carb. Just can't find the right side of the tool for it.

 

 

I recall that the 260 uses a WTE carb (we are all much more familiar with the WT) and the diaphragm kit for that is a K10-WTE, but many suppliers supply a K20-WAT in error. The difference is that the nipple in the centre of the metering diaphragm is flatter on the WTE one. A WAT one with a more erect nipple will cause over fuelling.

 

According to Walbro though, you still use the WT gauge , but just lift the arm a little more afterwards.

 

Another thought, but maybe a wild one, is this. You said it runs OK with the bar off. Could it be, by any chance, that clamping the bar up causes a crack in the crankcase to open? I seem to recall that this saw had some strange sort of damage done to it a while ago, or am I mixed up?

[Rich2484]

I recall that the 260 uses a WTE carb (we are all much more familiar with the WT) and the diaphragm kit for that is a K10-WTE, but many suppliers supply a K20-WAT in error. The difference is that the nipple in the centre of the metering diaphragm is flatter on the WTE one. A WAT one with a more erect nipple will cause over fuelling.

 

According to Walbro though, you still use the WT gauge , but just lift the arm a little more afterwards.

 

Another thought, but maybe a wild one, is this. You said it runs OK with the bar off. Could it be, by any chance, that clamping the bar up causes a crack in the crankcase to open? I seem to recall that this saw had some strange sort of damage done to it a while ago, or am I mixed up?

 

This is the saw overheated on the clutch. It then had an equation of, small child + flat head screwdriver + open exhaust port = damaged piston.

[spudulike]

Breathers come in different forms, some of the early ones were little more than restrictions in a pipe which allowed pressures to equalise but stopped fuel sloshing out. They worked both ways.

 

Modern ones tend to work only one way and prevent fuel escaping whilst allowing air in to equalise the pressure inside the tank with atmospheric pressure thereby relieving the vacuum caused by the depleting fuel quantity.

 

Most machines do not pressurise the tank, and indeed do not need to, as atmospheric pressure is sufficient to push fuel up the pickup hose to fill the vacuum caused in the fuel pump chamber by the pump diaphragm.

 

They do however pressurise to an extent by the vaporisation of the fuel as it gets shaken about and warmed up. it is this pressure that pushes the fuel out of loose pipes etc whilst servicing. This apparent pressurisation is not required to enable the engine to run.

 

Barrie - you are worthy to be on my thread:thumbup:

 

Well said and spot blinking on me old mucker:thumbup1:

[GardenKit]

Barrie - you are worthy to be on my thread:thumbup:

 

Well said and spot blinking on me old mucker:thumbup1:

Aww, shucks....was I right? Was only guessing!

 

Or maybe I have just been around a while.