Huge carb discovery <i think> main venturi seal spacer gap

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SinusoidalTendencies
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My tercel:: 87 4wd wagon

Huge carb discovery <i think> main venturi seal spacer gap

Post by SinusoidalTendencies » Tue Mar 10, 2020 5:39 pm

so i decided to measure some things. (any excuse to use a micrometer)

something about the rubber seal on top of the main venturi didn't feel quite right. not it being there but its thickness.

so...
from top carb upper mating surface with gasket to the hole above the main venturi
just a hair over 6mm. (6.2-6.3 maybe, getting a better micrometer asap)
from lower mating surface to the top part of main venturi. where the seal rests.
just a hair under 2mm. (1.9 maybe)

i've been using the seals that match what i've found in the 2bb aisins ive taken apart so far (the one in my 87 tercel4wd, and one off a nova 4ac)
and they measure a couple hairs over 3mm

if your any good with math you probably already see what i'm seeing.....there's gap. about 1mm-ish
IMAG1317.jpg
so out of the suitable spacers that came with the walker rebuild kit
IMAG1335.jpg
i started experimenting (so others can find available spacers in the same kit. have some other spacers in the extras i'm not sure where i got)

in this instance i believe bigger is better since rubber can squish a bit (within reason of course. 5mm would insure no gap & 4mm may leave .1 gap)

feedback please... is this the huge discovery i think it is? or have i missed something?
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Petros
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Re: Huge carb discovery <i think> main venturi seal spacer gap

Post by Petros » Tue Mar 10, 2020 10:44 pm

that is an easy gasket to leave out on reassembly, it will run, like crap, if you leave it out.

several times I took the top off my carb, leaving it bolted to the engine, to clean it out. a kind of quickly clean out and function check of internal parts. I replaced the accelerator pump, and cleaned out the scale and glaze build up inside the carb. that rubber gasket stayed stuck to the top, and went back where it was supposed to the first time clean it out. The second time it fell out of place, and I did not notice. I drove it but it ran like crap. Robert Walker (aka Xirdneh on this forum) told me about that rubber gasket when we met during a parts exchange, when I shared the trouble I was having with him. Sure enough, when I got it apart, no rubber gasket. I rummaged around until I found one that was close and use form a gasket to hold it in place, problem solved.

if you take these carbs apart very often, like Robert has, you figure this stuff out pretty quickly. there are a lot of tiny parts you have to watch out for. they are not hard to rebuild or clean out, but it is not a job for cluttered and messy shop bench. you need a clean surface and some means to keep the tiny parts in an orderly way, and refer to the carb diagrams often to make sure you get all the parts back in place before you put it back together.
'87 Tercel 4wd SR5 (current engine swap project)
'84 Tercel 4wd (daily driver, with on going mods)
'92 Mazda MPV 4wd (wife's daily driver)
'85 Tercel 4wd DLX auto(daughter's daily driver)
'01 Honda Civic (other daughter's daily driver)

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SinusoidalTendencies
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Re: Huge carb discovery <i think> main venturi seal spacer gap

Post by SinusoidalTendencies » Tue Mar 10, 2020 11:58 pm

petros... i'm surprised. it seems you completely glazed over what i was referring to in my post.

the size of it.
it does need to seal against the top of the carb right?
the bigger ones seem to be a better fit. will know better when i put it on and make adjustments in the daylight of course.
I don't always learn my lesson.
But when i do, it's the hard way.

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Petros
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Re: Huge carb discovery <i think> main venturi seal spacer gap

Post by Petros » Wed Mar 11, 2020 4:43 pm

I do not mean to diminish the importance of the height of the gasket. it fits up into a recces, and it must compress the correct amount for it to seal. Not enough and it does not seal, and too much it could swell into the passageway and cut it off.

my point is that often this compression gasket gets stuck in place, and you do not notice it is there. until it fall out during assembly, and after to get it to run.
'87 Tercel 4wd SR5 (current engine swap project)
'84 Tercel 4wd (daily driver, with on going mods)
'92 Mazda MPV 4wd (wife's daily driver)
'85 Tercel 4wd DLX auto(daughter's daily driver)
'01 Honda Civic (other daughter's daily driver)

User avatar
SinusoidalTendencies
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Posts: 143
Joined: Thu Sep 06, 2018 12:06 pm
My tercel:: 87 4wd wagon

Re: Huge carb discovery <i think> main venturi seal spacer gap

Post by SinusoidalTendencies » Wed Mar 11, 2020 8:16 pm

heck... i just spent the day trying to figure out all the different stop lever/tabs. sure it's in the fsm, but can you really tell whats being pointed at in the pictures. cause i can't. you almost have to bottom out the fast idle screw to even touch anything (let alone get the valve at a 20deg angle from horizontal. and in the picture it looks like your supposed to make the adjustment from the throttle side of the carb, but that screw doesn't change the valve angle at all.)

yeah, this carb is fun for sure....looks like ramen for dinner again
I don't always learn my lesson.
But when i do, it's the hard way.

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