Replicarburator Tuning?

MazdaMitch

Justa231v6 Yes you will see it happen.

Cusser

You can measure the ohms resistance of the choke heater.

You can also pull the air cleaner and apply 7 to 12 volts to the choke heater, and see if it warms in a few minutes or moves the choke butterfly.

With a cold engine, the choke butterfly should be essentially horizontal. With a warm engine or about 5-10 minutes of having voltage applied to the choke heater, the choke butterfly should be essentially vertical.

An operational choke heater is adjusted by rotating it after loosening the 3 retaining screws.

Justa231v6

thanks guys, i did check and its getting voltage. it just appears to be very slow to open.

MazdaMitch

Justa231v6 if you connect it to the back of the alternator (7 volt) it'll be slow. It is recommended to use 12 volt from Weber.

I found a 12v source when the key is ON using a test light, from the left over wires/plugs on the passenger side fender well.

Justa231v6

MazdaMitch i noticed that in your video, unfortunately i am not seeing the same harness in my truck. one of the previous owners did the change and i am not left with a mess to figure out. when i hit it with my meter though without the truck running i was seeing over 10v with the wire on it. i didn't check it after i started the truck as i started down another rabbit hole of fixing something else.

MazdaMitch

Justa231v6 Should be -0- voltage with the truck not running.

Justa231v6

MazdaMitch sorry should have noted that this was with the key turned. not "off"

Justa231v6

@MazdaMitch I sent a DM on FB.

but after watching your video about 3 times, i feel like i will give this a shot. at cold the flaps are about 66% open. I think its something i can do with an adjustment of the choke loosen screws and turn til it closes and is open just a touch or 7mm on the back side.

just wanted to go over the order to look at it to tune.

Choke
Idle screw
mixture?

then start looking at high idle if that fails? i never get the truck into high idle, it just wants to stall and i have to keep goosing to keep it running

MazdaMitch

Justa231v6

Hey thanks for watching.
Check out my YouTube channel I have several videos about the carburetor one of them is the fast idle cam video... there's an install video.. and then there's the tuning video, and a few more...watch them all you'll learn something every time.

If you want an order to tune lets try this
BASELINE
CHOKE
IDLE SPEED
IDLE MIXTURE
FAST IDLE

GET BASELINE SETTINGS OF YOUR CARB.
Before you mess with anything let's just get some baseline settings down.

With the truck off take your mixture screw and carefully screw it all the way in, but when it stops STOP! Do not force it, do not crank down on it. You can damage the needle tip of the screw.

Now look at the mixture screw..lets back it out, and count out two full turns from closed. This will get you in the ballpark, get it running and we can fine tune it later.

The idle speed screw, back it all the way out and now screw it in until it touches the throttle and wants to open the throttle plate and just go in one and a half turns. Again we can adjust this later this should get us going.

THE CHOKE
Things to know about the choke. It has a bimetal spring inside and when its cold its curled up tight, and when its warm or hot, it expands. This action is how the choke plate opens and closes.

When the truck is warmed up and at operating temperature the choke plates will be open pretty much all the way.

If it's not then you need to look at adjusting the choke.
Loosen the three screws and turn left or right to increase tension on the metal spring inside the choke. I think counter clockwise increased the tension on the plates.
That is why we hook a 12 volt power source to the choke, so that it heats up to bi-metal spring and opens the choke plates later.
Otherwise the engine will be too rich, not get enough air, and choke out.

In the fast idle video on youtube, that is kind of a 'cold start' video, and this is what should happen on cold start...
You press the gas, the tension from the metal spring in the choke, will close the choke plates all the way.
When the engine starts and runs, the plates will open about a quarter of an inch. This is by design and what is responsible for that action is the choke pull-off.
I discussed it in the fast idle video and the long tuning video.
The engine has to breathe, so that's what happens... it opens a little bit.

IDLE SPEED
You already have a baseline set, so with the engine warmed up, use your tach to dial it in. Get the idle speed to where you want it generally 850 RPM.

IDLE MIXTURE
Now you can carefully adjust the mixture screw and this is how I would do it.
While the engine is running, count your turns in from (2).
You turn the screw in some until the engine runs rough or worse, how many turns was it? Now back it out from that to fine the sweet spot.
You will know from how it sounds and runs.
Make of note of how many turns you are at.
It should be good at 1.5 to 1.75 out.
If its not, the idle air jet is too small.
If it runs best at 1 turn out and gets worse as you unscrew it, the idle air jet is too large.

But generally these carbs come with the correct jets. However we all live in different places and altitudes, so you make need to make adjustments.

FAST IDLE
Now that everything is pretty good, it sure would be nice to go out on a cold morning and press the gas pedal once, and crank it up, and it shoot up to about 2000 rpm, let it sit there for a few seconds, and lightly tap the gas one more time, and it idle at about 1100 rpm, then later press the gas and it drop down the 850 rpm.

That is where the fast idle comes into play.
There is a screw underneath the breather to adjust this and you adjust it on a cold morning on first start up. I went over that in the long tuning video and in the fast idle cam video.

Weber Documents and Tuning Guide
https://mazdaminitruckin.com/weber-documents/

Tuning Video
https://youtu.be/7S5CPHUfZs8?si=_07uU-ke38DjuoRL

Fast Idle Video
https://youtu.be/5Um8v28MijU?si=g5bvRvGnQuA_yKlY

Install a Weber Carb
https://youtu.be/YGww9NhyGbA?si=5bFW8xm1MMoHuhAv

Good luck with it!

Justa231v6

This helps a lot, i was messing with the regular idle and got it running better but will definitely be trying the process you outlined.

i will note when "futzing" with the choke loosening the screws and trying to turn clock/counter clock, the plates werent moving at all. I presume i was doing something incorrect. i will be messing with the fast idle screw tonight when i get home from work

MazdaMitch

Justa231v6 the spring may not be connected to the lever. Take the cover off, learn how it works and you see it has a small loop(hole) that the plate lever goes into.

Justa231v6

MazdaMitch

i notice the coil maybe tightly wound too. should it just be at rest? the majority of the time the truck is running the butterfly is completely open (except the first few moments before the goose after the initial start where the high idle should be, before the middle idle which both still need to be set)

MazdaMitch

With the choke cover off do you see the little metal protrusion inside and you can move it and it operates the choke plates do that to confirm that the linkage is hooked up.

Then you stick that little protrusion into the little hole of the spring and put it all back together and you should be able to operate the plates with the choke.

Justa231v6

ok so i had it running well... but i keep adjusting it runs great an then, i have to wait til it cools to see where the choke lays for cold. my last visit i am not sure what i adjusted with the choke but but butterfly was tight, but i was able to flip it open by taping it with my fingers. the fast idle screw was not even touching the cam. i will revisit that once i get the choke worked out.

question about the white plate inside of it. where should that opening be in relation to the poking part of the spring? centered or something else. clearly it needs to be in some part, i just don't know where. i had to take a break with a headache from being in the running garage for so long trying to get it right.

however it now starts, runs and doesn't stall. the last round the butterfly almost didn't open at all and that caused a rich condition where i was getting the headache. i tapped out of the garage for the night.

Justa231v6

Doing better today, but when the butterfly is all the way open it doesn’t close. Something is sticky.

Also, is this spring end supposed to be on the inside of the cam step? Currently it’s on the firewall side.