Vacuum Diaphragm testing. Have some leaks, and questions

[Erichimedes]

So, as per dlb's advice, I tested the vacuum diaphragms in my new (old) Tercel, and sure enough, found some busted ones. The ones I found leaking were:

-EGR. Just plugged the line, I'm ok not having it.
-The big double diaphragm under the distributor.
-The little double diaphragm on top and near the back of the carb. This one was fine if I disconnected both hoses and sucked on one side while plugging the other. However, sucking on either alone was no good. Is this one busted? It looks important.

The EGR I'm fine not having. How important to performance is the vacuum advance under the distributor? And I'm guessing the one on top rear of the carb is important. Can I buy that part? or do I need to find one from a salvage yard?

Thanks in advance!

[irowiki]

I bet I have a spare choke breaker on a seized carb. Rockauto wants $207 for a new one

Choke breaker:



Vacuum advance is important for fuel economy, but you can run without it if you plug Sadly I have no spares of those.

Did you plug the vacuum line for the EGR or remove the big metal pipe coming from the manifold to the EGR valve (and plugged that)

[dlb]

erichimedes, does your vac advance unit have two ports for the upper can? if so, make sure you plug one port while sucking on the other. otherwise it will just suck air through the second port. the lower diaphragm on the unit is separate from the upper though so you don't need to plug anything to test it. it is possible for just one of the diaphragms to be broken, in which case i have left the good one still connected while i've looked for a new unit.

the choke breaker also has two diaphragms, and each should hole air regardless of the other. if you're in doubt though, use the test in the FSM. it's very simple.

if you do need to replace it, i posted pics of how i replaced one of mine. the rivets mean getting a little creative but nothing too crazy.

https://tercel4wd.com/forums/viewtopic.php?f=4& ... =30#p63661

[Erichimedes]

dlb, when you say two ports on the upper can, do you mean the vacuum advance has 3 ports total? I didn't see the third one if it's there. I only saw two. I'll check again today.

I'm going to see if I can find the parts at the local yard. Headed out there tomorrow. It's kind of funny how much I like digging around in junkyards and stuffing my pockets with parts.

I'm excited to see the difference in cold starting with these replaced!

[irowiki]

Most vacuum advances in the junkyard will be bad.

If you find a tercel let me know, I need a 13" steel rim for a spare!

[dlb]

yeah, some vac advance units have 3 ports, some 2, and i think some of the first gen tercels only had one vac diaphragm on the advance unit, because emissions equipment varied by regions and marginally by years. so you have to take a look to see exactly what your car has. if you find a good 3-port advance unit, you can use that in your 2-port application. just plug the third port, the one with the smaller hole (that one is meant for the HAC). good luck!

[Petros]

if the vacuum advance on the distributor is bad it will not harm a thing to cap off the lines and run without it. Just set your static spark timing at 10 or 12 deg btdc. the only thing the vac advance does is when at cursing speeds, when the vac is high, it allows the spark to advance further to improve the fuel economy slightly. but I have not been able to detect the difference on mine when I put in a good one after driving for years with a leaky one.

At part throttle curising the fuel air mixture is low density and lean, the fuel burns slower so by advancing the spark it improved the efficiency a little. It will not harm anything to run without it, most cars did not even have a vac advance until after about 1974, the six cars I owned never even had them.

Just make sure you cap off the vac lines that run to it, you do not want the leaky diaphragm to act like a vac leak.

[Erichimedes]

Thanks guys. I may just leave the vac advance alone if I can't find a good one for cheap. I would like to replace the choke breaker, if at all possible. It's pretty cold around here in the mornings. I just have to figure out how to get rivets off in the middle of a junkyard. The local guy wants an arm and a leg for junk parts, so I may not be able to afford the whole carb. We'll see!