Terc delight

[irowiki]

That means your AAP is probably ruptured.

[Gottolovem]

As petros points out it can only be a couple things and the dissy i gave you is a known good dissy.
So now you are at fuel if you find nothing wrong under the valve cover and there is gas in vac lines.
And this is the same symptoms You had before you changed the engine it has to be one of the components!
I say change the carb with all it's various bits and pieces?
And wouldn't you know it i have one you can use to trouble shoot the issue

Loren i will be happy to try and help you figure this out just say the word you seem to be pretty savy though.
Don't start throwing new parts at it until you figure it out you can borrow them from me to save money.
It still is bizarre that only one cylinder is giving you fits.


UPDATED compression readings on my rust bucket 125 all across excluding number 2 It's dead 25 was the highest reading I could get

[KZ750]

Got it whoop whoop! and now I have to leave for work.
I tightened down some vacuum lines and did a second once over on the routing and now it's all good.
The aap is indeed ruptured, so i capped it off. I'll get back to everyone tonight when I'm not running out the door.

[dlb]

BAM that's your problem. the AAP is connected to the lowest port of the TVSV which is connected through the second lowest TVSV port to the intake manifold port. when the AAP is ruptured, manifold vacuum can suck gas through the ruptured AAP, through the TVSV, and into the intake manifold.

and surprise surprise, the manifold vacuum ports are located on the first cylinder runner of the intake manifold, which explains why your first cylinder spark plug was drenched and not firing. it was too rich to run.

the AAP can be left capped for now but it is very easy to replace without even removing the carb. you can either get a good used one from another carb or you will need to buy a carb rebuild kit for a new one.

can't wait to hear how things run with this issue finally sorted out!

[Gottolovem]

SWEET
Now you need to go stretch her legs out
did your engine come with a break in procedure?

[irowiki]

Your TVSV is probably bad too if it has been soaking in gas long enough!

[dlb]

Your TVSV is probably bad too if it has been soaking in gas long enough!

the TVSV shouldn't be affected by gas. it is basically just a plastic cylinder that is pushed up and down the plastic housing so i don't think gas should do much to break the plastic down. however, like i've said lots before, i've yet to find an old TVSV that passes the FSM test procedures so i would wager KZ750's is also worn out (unless the car is obscenely low miles).

[irowiki]

I was reading on these forums that people with bad AAP's tended to nuke the TVSV's too.

Isn't there rubber in there to seal it?

[dlb]

it's been a while since i had one apart so you could be right but i seem to remember the cylinder inside the housing was quite hard and rigid, just like the housing. i have found the failure point is not the seal between cylinder or the housing but the steel pin and the hole it lives in, in the base of the TVSV: after going up and down so many times, the steel pin wears away at the brass base so that the two do not seal very well. then, as the coolant heats up, it can only push the pin 1/2 way up before the seal is broken and the pin can go no further. this is why all the TVSVs i have tested do ok for the first two temp stages but fail the third.

if gas were to break down a TVSV, it would eat at the cylinder and housing and allow all five vacuum ports to be linked, which would obviously spell chaos for all driveability--all of the vacuum operated devices connected to the TVSV would not function and there would be a few big vacuum leaks. i don't think the engine would run in those conditions...that being said, i've seen tercels run ok with all kinds of other major issues so who knows!

[Gottolovem]

I bought a t4 with the tvsv broken in half and the car ran ok. when i replaced it the car ran better and passed smog.
I don't recall there being a huge difference In the before and after?

[dlb]

I bought a t4 with the tvsv broken in half and the car ran ok. when i replaced it the car ran better and passed smog.
I don't recall there being a huge difference In the before and after?

that's surprising because with the TVSV broken, there would be one manifold and two ported vacuum leaks, plus the choke breaker, choke opener, AAP, and EGR would not function, and the EBCV would only partially function since vacuum switch B would receive no vacuum.

having the EGR disabled would not be an issue but i have found the AAP and choke breaker to be pretty important to cold running. with just a ruptured choke breaker diaphragm A, one terc i had would barely idle when cold. i've never had problems with a choke opener but i think xirdneh mentioned once that it keeps the choke valve from flapping around once the engine is warmed up. i'm not too familiar with the EBCV so i'm not sure how much of an effect it would have if only partially functioning.

i think that if you replaced a broken-in-half TVSV and didn't notice much of a difference, there were likely other emissions/cold running/carb issues going on at the same time. that's been my experience anyway.