Impulse Hose

[spudulike]

er... it is in the name...a pump...pumps and a meter.....well it meters out fuel in the correct amount!

In a saw, the fuel is typically held below the carb. Liquid doesn't run well upwards so the saw uses the positive and negative pressure of the crankcase to pump the fuel upwards in to the carb by use of a pumping diaphragm in the carb.

[Macpherson]

2 hours ago, lurkalot said:

Not sure you "simplified" it to be honest.  It doesn't cause the metering, the metering is a separate thing.  It makes the fuel pump work as I already explained.  The pump feeds the metering reservoir.  Metering is a separate operation altogether.    But who am I to speak on such things, I've only been repairing this stuff for 4 2 years.  In future I'll keep my help and  advice to myself.  

So your probably quite young then.... how could you possibly know anything.....?....I have to say that I totally agree with your last sentiment.

[bmp01]

23 hours ago, peatff said:

 

I over simplified it but in my understanding he asked about what the impulse hose does and it does all the pumping and causes the metering which is the part that is affecting the fact that his saw won't run. Apart from it being Chinese.

That's a good video, explains it well. Unfortunately the guy said 'metering diaphragm' once by accident when he meant 'pump diaphragm' , maybe that's what has caused confusion amongst respected members on here?

Can't say I've seen 3 one way valves in the pump most have 2 flap valves.

That aside, really good schematic, model and voice over.

 

 

 

[spudulike]

8 hours ago, bmp01 said:

maybe that's what has caused confusion amongst respected members on here?

 

 

 

 

Now he is calling us members - isn't a member another name for a blokes appendage.....i.e. cock 

 

[bmp01]

37 minutes ago, spudulike said:

Now he is calling us members - isn't a member another name for a blokes appendage.....i.e. cock 

 

Spud, don't be a cock, ye cocky 'ol cock ....

 

 

Edited November 15, 2018 by bmp01

[spudulike]

1 hour ago, bmp01 said:

Spud, don't be a cock, ye cocky 'ol cock ....

 

 

Ya bloody big member

[adw]

Well lets keep it going, what happened about atmospheric pressure on metering diaphragms? and throw compensator carbs into the mix that should keep the thread going!

[spudulike]

Unless the OP is dragging his Einhell up Ben nevis, I think altitude in the UK doesn't come in to this issue!

Thought you had become a Trappist Monk!

[openspaceman]

Good to see you posting again adw

[GardenKit]

Crikey, this is a very informative thread with contributions from some of the most knowledgeable members (and I don't mean "clever dicks"!).

Something that was drummed into me during my education, many years ago, was that we all use the term 'vacuum' in the wrong sense. We refer to diaphragms being pulled down by vacuum, but in fact they are pushed down by atmospheric pressure into the void of lower pressure beneath.

The lower pressure is caused by the venturi effect of the rush of air over a restriction in a passage (higher pressure one side of restriction, lower pressure on the other, or, in the case of the crankcase it is the drop in pressure felt when atmospheric cannot get into the cylinder fast enough.

So the atmospheric pressure plays a big part in carburation, hence the need for re-tuning or even re-jeting at altitude.

 

My college lecturer insisted that there was no such thing as suction, my girlfriend at the time however, disagreed.?