Vacuum leak within 1406 carb?

-
H22A4

H22A4

Does anyone read this?
Joined
Aug 4, 2006
Messages
3,042
Reaction score
2,294
Location
YVR
I upgraded my 318 to a 4bbl late last year and have been trying track down a vacuum leak ever since. I haven't taken the carb (1406) apart yet but have traced (using a tube with one end held to my ear) it coming from the secondary chamber/opening. It's a noticeable hissing noise that doesn't disappear even when the air cleaner is on. Also, when the engine is cold, there is no leak/sound. Only after its been running for a minute or two do I hear the noise and it remains even after restarting if the engine is still hot. Any suggestions on what it might be before I open the carb?
 
Does the carb have a hot idle compensator......

hot-idle-compensator.jpg
 
You MUST use a 4 barrel intake when using a 4 barrel carb you know.


I noticed one day that the linkage on the passengers side of the carb was just slightly holding the secondaries open on mine.
Bent the little tab that is connected to the secondary butterflies shaft away from the main linkage just a hair and that did it.

Also, if you are just hearing a noise and no other indications of a vacuum leak it may not be a vacuum leak, but a base gasket vibrating as the air goes by.
 
Thanks for the suggestions so far. The instruction manual/parts list for the 1406 doesn't list a hot idle compensator.

If either of the secondary butterflies isn't closed, then I guess bending it would solve it?

Yes, the 1406 is on top of a LD4B.
 
DO NOT bend a butterfly!
I believe the instruction manual says to back out the curb-idle screw until no longer in contact with the stop, and then to measure the air-gap on the secondary actuator. This assumes the butterflies are centered in the secondary shaft and both are sealed to the bores. They should remain this way after the curb-idle is returned to it's former adjustment.
Sometimes if the engine is not receiving enough idle-advance, a guy might screw the curb-idle screw in too far,cracking the secondaries. Watch out for this.
This can also upset the transfer-port sync, and may make the engine either idle crappy, or initiate a hesitation on throttle tip-in. The relationship of the transfer port to the butterfly is pretty important. For help in setting this, click on the little blue M below in my sig.
 
Last edited:
AJ/FormS can you empty your inbox?
 
You must log in or register to reply here.
-

Back
Top