Homelite procedure for carburetor pressure testing

[Clasec]

Here you go Dan.                                                                                                                                                                                                                                                                                                                                                            Carburetor test instructions -1 by Clasec, on Flickr                                                                                                                                                                                                                                                                                                          Carburetor test instructions -2 by Clasec, on Flickr                                                                                                                                                                                                                                                                                                        Carburetor test Instructions - 3 by Clasec, on Flickr                                                                                                                                                                                                                                                                                                    Carburetor tester by Clasec, on Flickr                                                                                                                                                                                                                                                                                                                      Carb. tester by Clasec, on Flickr

[sweepleader]

This is great stuff, now everyone can know the correct steps.

[riseandrun]

May I ask a few questions..., 1. what is the difference between an independent and dependent carburetor? and 2. for the Independent carburetor on step 3, is the balance tube mentioned the same as the primer? It's good to not have to guess if the carb. is good or not. This test procedure pretty much rules out a carburetor problem correct?
Thanks for the info.
R&R

[Clasec]

Nov 29, 2020 19:26:49 GMT -5 riseandrun said:

May I ask a few questions..., 1. what is the difference between an independent and dependent carburetor? and 2. for the Independent carburetor on step 3, is the balance tube mentioned the same as the primer? It's good to not have to guess if the carb. is good or not. This test procedure pretty much rules out a carburetor problem correct?
Thanks for the info.
R&R

HDC fuel circuits by Clasec, on Flickr

[okie]

I've notice that when testing the Homie EZ Walbro HDC carb that the procedure on pg2 step IV indicates to open either the low or high jet.
Opening the low jet would not let the pressure drop. I even took the L jet completely out and no pressure drop. Only opening the H jet would let the pressure drop.
AND
The carbs ran and adjusted great when on a saw.

[hotshot]

Mar 6, 2021 16:32:42 GMT -5 okie said:

I've notice that when testing the Homie EZ Walbro HDC carb that the procedure on pg2 step IV indicates to open either the low or high jet.
Opening the low jet would not let the pressure drop. I even took the L jet completely out and no pressure drop. Only opening the H jet would let the pressure drop.
AND
The carbs ran and adjusted great when on a saw.

You need to stay calm Okie!

The reason is that the HI or Low needles on a HDC carb have nothing to do with pressure drop while pressure testing only the inlet needle.

IF it holds 8# pressure, that’s a pass.

IF you then depress & hold the metering diaphragm button AND you have both the needles tightly closed, THEN the 8# test pressure will slightly drop, as the metering chamber is filled up with air.

On an independent HDC carb, THEN opening up either needle will release pressure.

On a dependent carb, as in your case, THEN the HI needle only will release the test pressure. The Low needle is fed from downstream of the HI needle passage.

Those HI & LOW needles are always opened to operate a saw, so I think that needle test is bogus anyways...

[okie]

hotshot:
You wrote this
On an independent HDC carb, THEN opening up either needle will release pressure.

and then this statement:

On a dependent carb, as in your case, THEN the HI needle only will release the test pressure. The Low needle is fed from downstream of the HI needle passage.


Question:? Just want to clarify.
Are you saying that HDC carb's are made as both dependent or independent TYPES?

I suspected what you say about the needle tests being bogus due to having to be a total blockage of the jet to fail such.
Those tests procedures would have really had me digging back into the HDC LOW JET AREA failing the test if I had not know for sure that I was testing a good running carb.

[okie]

Mar 10, 2021 10:46:53 GMT -5 okie said:

hotshot:
You wrote this
On an independent HDC carb, THEN opening up either needle will release pressure.

and then this statement:

On a dependent carb, as in your case, THEN the HI needle only will release the test pressure. The Low needle is fed from downstream of the HI needle passage.


Question:? Just want to clarify.
Are you saying that HDC carb's are made as both dependent or independent TYPES?

hotshot: I see in the diagram above and at the Walbro site that some HDC's were MADE as independent types meaning that opening the L jet will cause the pressure drops. Thanks for waking me up and I did stay calm while re-searching.

I suspected what you say about the needle tests being bogus due to having to be a total blockage of the jet to fail such.
Those tests procedures would have really had me digging back into the HDC LOW JET AREA failing the test if I had not know for sure that I was testing a good running carb.

[okie]

Here is a link to the walbro site to see a full view of the HDC jet ports:
notice port 9, 10 and especially 11 which is the idle port inside the cab throat and I carefully try to make sure the idle port is open using a tag wire and low pressure air when I'm having idle issues.

www.walbro.com/wp-content/uploads/2016/01/HDCseries.pdf

[ruffcut]

I need to know if this procedure will work on a Walbro SDC-74 carb with a fixed jet? If I'm reading the service bulleting for the SDC carb, it should be an independent carb? This carb is coming off a 1130g. I'm having issues with it being too rich with no high speed.

[onlyhomelites]

The dependent hi-lo means the carb draws fuel for both circuits from the same source...I don't believe that is the case with the SDC-78 The only test you wont be able to perform with a fixed high speed jet is the one where you close off the high speed needle. Everything else should work the same.