Does a diaphragm sit still or move vigorously in high speed operation?

[chy_farm]

Have you ever tried to give consideration to the invisible movement of a diaphragm in a small chamber of a carburetor in operation?
Does it move or is just sitting still? If it moves, how? , at what cycle it moves to fill the fuel?

This is a short report on it with some technical data. I hope you enjoy it.
------------------------------
[Detecting System]

The detecting system I used for this experiment is ;



This saw sitting in the left is a well known McCulloch 10-10, a handy medium class saw I love, installed with a vibration detector. This vibration detector is especially for metal, which was made by a friend of mine some 11 years ago when he was alive. He was an owner manager of a very skilled vibration research laboratory who have been selling precision vibration simulators to almost all of the world leading auto companies. He was a very efficient adviser on vibration study for me, I am glad to be able to tell some about him here in the memory of his.

[Vibration Detector]


From the black part in the center, magnetic flax comes out to generate an 'eddy current' on a metal surface. Then this eddy current generates a new magnetic flax when a detecting metal moves back and forth. And again this black part catches this new magnetic flax and then gives changes to the current which go through this black part.
So we can detect this change in the current to know there is a movement on that detecting metal.


Chy

 

[afleetcommand]

Hoping it "cycles" matching pulses from engine RPM...but have to wonder if at some point the rpms are so fast there is no way for the diaphragm to move a full stroke, so it begins to flutter with less amplitude as the frequency of the pulse gets past a certain RPM?? Based on the mass and spring characteristics along with the dampening effect of the fuel?? Now that you brought this up..... I'm curious. Love conversations like this... Wonder if there is diaphragm float like there is valve float! AND is there a limitation on how many continuous RPM's a diaphragm carb can feed a motor? OR does it go into some harmonic still cycling enough to move fuel along..curious minds want to know.

 

[chy_farm]

Good morning and a Happy New Year Afleet, thanks appreciate your deep consideration on this! Yes what you stated is just what they wondered in another forum too. Glad you like it!
Chy

 

[gduvic]

 

[KYsawman]

This is very interesting, I love the information from your builds. I have a John Deere badged echo 302 headed my way.. I may be hitting you up for some echo help!

 

[chy_farm]

Hello KY, hope you have a happy new year.
Glad you like this. I love John Deere Echos too, the color scheme is even better than the original, IMHO. I have an Echo 302,

but not yet tinkered her, she is sitting still in my shed now lol, hope I have something to help you on her but I yet know much about it though.

 

[chy_farm]

[Detector Housing]

The structure of the detecting unit is like this below, the tri-ped post for the detector is made from copper wire, holding this blue detecting terminal in the center.

 

[Marshy]

Interesting.

 

[USMC615]

Interesting x 2!

 

[Stump Shot]

It is interesting as just what goes on here. I can picture a metering diaphragm just staying open at some point, but at the same time I can't picture the same happening with the fuel pump flaps, for if they did would it still pump fuel? Or once the flow starts it just gets pulled through? Very hard to picture at extreme RPM of these little motors. Hope Chy can shed some light on this.

 

[Chainsaw Jim]

Ok... here goes. Lol



The two stroke pump carb works in a similar way to one of these hose siphon fertilizer containers. Only instead of water creating the vacuum, we have air flow.
As the air passes by the main nozzle/check valve at wot...



...it pulls fuel from these jets and passages...


...and since the entire area (pan) is filled with fuel underneath the metering diaphragm, the pulled fuel will create a vacuum which pulls the diaphragm down to open the metering passage, allowing more fuel in.

At wide open throttle the fuel flow is constant enough to hold the diaphragm down to match flow.
The choke blocks off the carb so the vacuum on the fuel line is increased considerably, allowing a strong siphon effect to pull fuel all the way up from the tank in a couple pulls. At this point the piston is creating the pumping before the combustion can take over.

The pump side is controlled by the piston impulse which pushes and pulls on the fuel at the pump flaps.

One of its functions is to help pump fuel when starting cold. Another function is to allow the check valve to check up without pressure blowing by it. As the piston travels downward the impulse pressure closes the flaps to aide the function of the check valve to prevent seepage between strokes to prevent fuel puddling at the intake.
The diaphragm shouldn't be vibrating or appear to be pumping aggressively because there's more fuel stored in the pan that what can be used in one stroke. It would appear to float softly if any movement was witnessed.
The pump flaps move as fast as the piston moves, which is why you'll see different performance grades on pump side diaphragms...the blue plastic, black rubber, and the tan woven.

I forgot to mention the little holes in the carb throat called idle holes are also fed the same way.

 

[chy_farm]

Interesting.

Interesting x 2!

It is interesting as just what goes on here. I can picture a metering diaphragm just staying open at some point, but ---------------Hope Chy can shed some light on this.

-----------
The diaphragm shouldn't be vibrating or appear to be pumping aggressively because there's more fuel stored in the pan that what can be used in one stroke. ------------

Good morning guys, many thanks, glad to know you have a lot of fun on this theme. To me the movement has long been under the veil, hope it will come up to us with its true performance.

 

[chy_farm]

[Phenomenon and the structure]

Lets see the structure in my drawing;


Please keep in mind that this illustration is drawn up-side-down, these black lines with black circle signify the current given by this vibration detector . The diaphragm is illustrated as a square plate painted in pale blue at the bottom.

1:
First the current runs through the black lines and circle, and it generates the magnetic flux(green arrows).

2:
Green arrows(magnetic flux) reaches the metal plate, and this magnetic flux given to the plate generates circular electric current on the metal when this metal moves up or down.

3:
Then this electric current said above generates another magnetic flux which reaches to the sensor circle(pink circle) to give electric current to this sensor circle.

4:
We can see the changes in the voltage of this electric current above through amplifier set after this sensor.

Chy

 

[chy_farm]

[Pulser Coil and Pulse Signal]

A detecting monitor can be an oscilloscope, or a note-PC as a data logger. The signals to be recorded are firstly ones from the movement of diaphragm, secondly the timing signals that come with the ignition sparks. So we detect two different signals from the motor.

The pic below shows I was making another pulser coil next to the ignition.







I wound the wire 150 times, which gives nearly the half of the primary current as you see in a oscillo view above, which is a little too much. Less than 35-turns is enough now I suppose.

Chy

 

[Marshy]

Did you think the diaphragm pulse will remain 1x running speed?

 

[chy_farm]

Did you think the diaphragm pulse will remain 1x running speed?

Hello Marshy, yes I thought in that way.
Chy

 

[MattG]

@chy_farm

You might find this of interest. The Zama C1Q-S126B fitted to certain european MS200Ts, has it's impulse port blocked/blanked off by the factory. Seriously. Check out these pictures:

The carburettor I have above is malfunctioning for another reason (I think that it has blocked internal low speed drillings/jets etc). However I have always been puzzled as to why the above port was deliberately blanked at manufacture, and yet can still pump fuel.

In my latest experimentation, with the knowledge that the carburettor will not leak any air through this blanked port I successfully start and run the saw, without the impulse line plugged to the carburettor at all. Notice the loose looking tube which I have blocked with a green bung in this video clip:

 

[chy_farm]

@chy_farm
You might find this of interest. The Zama C1Q-S126B fitted to certain european MS200Ts, has it's impulse port blocked/blanked off by the factory. Seriously. Check out these pictures:------------

Hello Matt, indeed it's fun to see. It may sounds odd, but my question is if this carb you have introduced above does not have another inlet port at the other side of its pump cover, e.g. a pic below shows a carb on my on-going McCulloch 975 project, which has an impulse port and a fuel port;



Chy

 

[MattG]

It may sounds odd, but my question is if this carb you have introduced above does not have another inlet port at the other side of its pump cover,

Hi Chy,

No, it genuinely just has the impulse line to send a pulse to the pumping chamber in the carb. Lots of other carbs with a very similar designation e.g. S126A do have this port, but as per usual it has an opening here through to the pumping chamber. For some reason the S126B does not. Instead the port is blanked off. Presumably it can rely of vapour pressure in the tank, capillary action in the pipe, and the venturi effect in the carb throat to suck the fuel through.

It is currently a mystery to me.

 

[Chainsaw Jim]

Hi Chy,

No, it genuinely just has the impulse line to send a pulse to the pumping chamber in the carb. Lots of other carbs with a very similar designation e.g. S126A do have this port, but as per usual it has an opening here through to the pumping chamber. For some reason the S126B does not. Instead the port is blanked off. Presumably it can rely of vapour pressure in the tank, capillary action in the pipe, and the venturi effect in the carb throat to suck the fuel through.

It is currently a mystery to me.

Most carbs have a little casting mark to pinpoint where to drill the hole if the carb is designated for an intake block set up. Here's a WJ39 from a husqvarna 394, and a WJ48 from a stihl 066.


You say the carb you pictured has a problem. You will likely need to drill a hole in the location pointed out to complete the impulse passage.