Checking Choke-pull off functionality

[darth_linux]

I'm working on a mid '60s Stromberg WWC, and I'm checking the choke pull off. Begins to move with 5 mmHg and is completely engaged by 10 mmHg. Is somewhat slow to release if over-engaged - maybe sticking. Does anyone have a known-good or NEW unit to compare with mine? Wanna compare if mine is opening at the right time. OEM P/N is 2448971. (Choke Pull Off Vacuum Break 2448971 Stromberg Bendix 1964-1967 MOPAR 273-318)

thank you!

 

[CBODY67]

There are no real specs for choke pull-off performance. Either they hold vacuum or they don't. With the normal check to be to remove the vac supply hose, manually compress the plunger, put a finger over where the vac hose attaches, then release the compressed plunger and see if it extends. In some cases, it might extend minimally, then stop. If it passes that test, it is good. If the plunger extends freely, then the diaphram inside is ruptured/broken. Which means "replacement time".

In some cases, a leaking diaphram can be over-ridden by a strong vacuum supply from the engine, with it still operating as desired. But not passing the test mentioned above.

Also note that on the end of the tube the vac supply hose attached to, is a small hole rather than a big hole. This is a restriction to prevent the vac area from being evacuated too quickly, which might compromise the durability of the vac diaphram inside of it. And it also dampens the extension of the plunger, too. Operationally, should manifold vac be greatly decreased during choke operation (as on a cold engine), the choke valve will close gradually rather than shutting quicker via the choke thermostat's spring pressure.

In shopping for a replacement, NOS might not be the best choice, as that means the rubber diaphram is quite old and might fail sooner than suspected. Which means a replacement in an aftermarket brand MIGHT be a better choice, as it might be "younger" than the NOS Chrysler part. Just make sure that what you get matches what is on the car now.

Enjoy!
CBODY67

 

[darth_linux]

There are no real specs for choke pull-off performance. Either they hold vacuum or they don't. With the normal check to be to remove the vac supply hose, manually compress the plunger, put a finger over where the vac hose attaches, then release the compressed plunger and see if it extends. In some cases, it might extend minimally, then stop. If it passes that test, it is good. If the plunger extends freely, then the diaphram inside is ruptured/broken. Which means "replacement time".

Also note that on the end of the tube the vac supply hose attached to, is a small hole rather than a big hole. This is a restriction to prevent the vac area from being evacuated too quickly, which might compromise the durability of the vac diaphram inside of it. And it also dampens the extension of the plunger, too. Operationally, should manifold vac be greatly decreased during choke operation (as on a cold engine), the choke valve will close gradually rather than shutting quicker via the choke thermostat's spring pressure.

In shopping for a replacement, NOS might not be the best choice, as that means the rubber diaphram is quite old and might fail sooner than suspected. Which means a replacement in an aftermarket brand MIGHT be a better choice, as it might be "younger" than the NOS Chrysler part. Just make sure that what you get matches what is on the car now.

Enjoy!
CBODY67

Thank you for the reply. It does indeed hold vacuum, so I guess I'm good. I'm honestly surprised as this carb has been sitting in a box for at least 20 years before coming my way. I'm getting ready to tear down the carb, rebuild it, and just got a vacuum pump/test kit so I figured I'd check and see if the pull off was going to work for me. Pleasantly surprised!

thanks again