Fine Tuning Weber 32/36 with Wideband

[Mucci]

So I finally got my Wideband setup and have been trying to fine tune my Weber 32/36 but I’m having trouble finding information on what passages are active at what throttle positions.
 

I’m used to tuning motorcycle carbs and there is a popular graph that shows which jets/passages are active during different throttle positions.
 

Does something like that exist for the Weber 32/36?

I’ll preface by saying I’ve already gone through and verified my ignition timing at all RPMs and have gone through the Weber tuning guide to get the car running pretty well. 
 

 Currently my best idle is 2 turns out at 12.5 AFR. 

My cruising AFR at 1/4 throttle is pretty rich at 12.5.

Part throttle acceleration is also around high 12’s. 
However WOT at high rpm is 14.5-15. 
 

How do I lean out my partial throttle range and richen up at full throttle?

 

Edited October 18, 2021 by Mucci

[uai]

Make Idle Jets 5 smaller and main Jets 5 larger.

If it runs well I wouldn't worry at 12.5 as being too rich - if it behaves well it's ok even at idle or cruising. 

Edited October 18, 2021 by uai

[TobyB]

Quote

what passages are active at what throttle positions.

Oooh- you're going to love this- it depends partially on RPM!

 

That said, for what you've described, to richen full throttle, go bigger on the main jet

for the larger barrel, if you need more fuel at lower revs.

If you also need more at higher revs, you may also

end up going smaller  on the secondary air corrector.  But do the main first.

 

At cruise, you're playing with the primary.  If it's light throttle, light load cruise,

try going smaller with the main by 1.  You also could try going bigger with the

air corrector if it trends richer as revs and throttle position increases.

 

The stinker with the 32 is that you really need to know berjactly when the

secondary's opening.  It's really hard to feel- the one try I had at tuning one,

I stuck a big spring on the secondary just so I could rest on the throttle with it closed.

You can also disable it, but then you get lots of conditions that are never

replicated with it enabled. 

But once you do that, it behaves like any other Weber, and most other fixed- venturi carbs.

 

https://www.lainefamily.com/images/WeberTuningManual.pdf

has the best pictures on the island.

 

t

 

[Mucci]

I did notice the AFR leans out as I get higher in the RPM range. If I understand it correctly that's the air correctors coming on?

 

How much effect do the secondary passages have on AFR prior to the linkage being engaged?

Is idle AFR a 50/50 split between primary and secondary idle jets when both TB's are closed? (or maybe more accurately, a 53/47 split?)

Are the idle jets active throughout the entire throttle range?

When do the mains start to come on?

[John76]

Can you share your jetting recipe and timing?

Stock engine (except Weber 32/36) ?

Stock exhaust ?

I built a micro switch for the Weber to tell exactly when the secondary starts to open.

I was curious as to how fast you can cruise while still on the primary circuit....answer: about 80mph (w/ 3:64 diff and stock wheels)

PM me and I'll be glad to send it to you.

John

 

 

 

 

['76mintgrün'02]

7 hours ago, TobyB said:

The stinker with the 32 is that you really need to know berjactly when the

secondary's opening.  It's really hard to feel-

 

It is easy to see with an AFR gauge.

 

Speaking of fine tuning, I made an adjustable "loose lever" to bring the secondary in sooner and shared it in this thread.

 

 

I just ordered ten links from Pierce Manifolds, so I can make a little run of them.  A few are spoken for already, but I'll bump that thread in hopes of peddling the rest.

 

The classic c.d.eisel jetting prescription is working well for me.  I went a little larger on the primary air corrector to lean it out a bit.  His prescription is available in the articles section.

 

 

Tom

[Mucci]

1 hour ago, John76 said:

Can you share your jetting recipe and timing?

Stock engine (except Weber 32/36) ?

Stock exhaust ?

I built a micro switch for the Weber to tell exactly when the secondary starts to open.

I was curious as to how fast you can cruise while still on the primary circuit....answer: about 80mph (w/ 3:64 diff and stock wheels)

PM me and I'll be glad to send it to you.

John

 

 

 

 

I'm purposely not sharing my mods or jetting recipe to avoid numerical prescription. I won't learn anything that way.  I'm looking for information on exactly how the carb meters air/fuel within different RPM and throttle ranges. Once I understand that process I'll know where to pull and push jet numbers based on what the wideband log.

I'm a little hazy on why it's critical to know exactly when the secondary is coming on. I read somewhere that the procedure is to get the primary jetted accurately and then step all the secondary jets down .05 from there (i.e. 145 p. main / 140 s. main). Is that accurate? Is that rule of thumb reversed for the air correctors? ...meaning secondary air corrector would step UP .05?

How does the above method work for testing primary main jet at 2/3-WOT throttle position since that's secondary territory?

[TobyB]

Quote

• 1 I did notice the AFR leans out as I get higher in the RPM range. If I understand it correctly that's the air correctors coming on?

 

2 How much effect do the secondary passages have on AFR prior to the linkage being engaged?

 

3 Is idle AFR a 50/50 split between primary and secondary idle jets when both TB's are closed? (or maybe more accurately, a 53/47 split?)

4 Are the idle jets active throughout the entire throttle range?

5 When do the mains start to come on?

 

6 I'm a little hazy on why it's critical to know exactly when the secondary is coming on. 

1- yes, if you're fully up on the main jet in that barrel.  The 'curve' of the a/f ratio towards lean in your case indicates that more air than fuel's coming in as revs increase.  The way to reduce air is with a smaller air corrector.

 

2- none, if I remember right

 

3- I recall the secondary being pretty much fully closed at idle, with the engine running on the primary's 

idle and progression jetting.

 

4- yes, take a look at the pdf link I posted above.  However, the vacuum signal to the idle and progression

circuits drops off a lot as the throttle opens, and that, along with the massive increase in airflow, reduces their

effect on mixture.

 

5- when there's enough airflow past the aux venturi to overcome gravity and start pulling fuel out of the

main circuit.  It's a really 'soft' start, determined by throttle position and revs.  If you whack the throttle

wide open from idle, the mains won't come on until the pump jet shot gets revs up.  You can test

this by closing off the mains passages.  You get a BrrrAAAPPP that dies almost immediately, but

the engine will rev pretty high on that shot.

Yep, I've had a plugged main jet before!

 

6- it matters because you want to be tuning the correct barrel.  When the secondary starts opening,

it initially steals airflow from the primary, and so while power, revs, etc are increasing, the flow through

the primary decreases at first, in some circumstances.  The secondary needs to be able to function 

in concert with the primary, and it's doing so in a non- linear environment.  It can also be doing it in

significantly varying states of flow, as it opens mechanically, so the driver can open and close

it at anywhere from idle to about 4000 rpm.  So it gets frustrating if you don't know if the secondary's

started to open and has too small a main jet OR if the primary's going lean on the air corrector, for example.

 

hth

 

t

[Mucci]

Thanks again for all the info Toby. I opened your pdf at work then realized it’s a Sunday morning with coffee and time to kill kind of read. I’ll get to it soon. 
 

I thought this was making a lot of sense until I tried to put it to the test tonight. As stated before I had a rich condition at partial throttle - low rpm and a lean issue at WOT high rpm. My idle is within spec so I went +.10 on the primary air corrector and -.10 on the secondary corrector. 
 

This solved my part throttle rich condition a bit so that now I’m cruising at 13.5-14.2 (better) however my WOT now leans out to 15-16.5 at all rpm!

 

I’m not sure why it’s leaning out more at WOT after reducing the secondary air corrector. My next move is to bump up the secondary main .05 in hopes that it’ll only add fuel to the top end range. That sound right?

 

 If the secondary idle jet doesn’t come on until the secondary starts to open at 2/3 throttle why is it called an idle jet?

 

Another question…what kind of problem would a pump jet step up be the solution for? Just curious as I’ve got a 55 (+.05) single sided pump jet in the Weber kit. 
 

 

Edited October 19, 2021 by Mucci

[TobyB]

That's a bit odd- but what it seems to be showing is that the primary air corrector's a big factor when

you're at WOT. 

Given that the smaller secondary air didn't balance that, yeah, exactly- go bigger on the secondary main.

Since the secondary's larger AND more throttled, it's less on the air corrector

than the primary.  And it's really important to note revs while all this is going on, as that's a

pretty good indicator of flow.   That's what the jet stacks respond to- the draw across them.

 

I logged revs and AFR for tuning, and it made it really easy to see the curves, and the changes

that an air corrector change made on them.  It's a 'skew' factor that rolls the top 'half' of the

effective range of the carb barrel leaner or richer...

 

I have no clue what the idle passages in the 36 barrel are for- maybe to get the thing to transition

evenly to controlled flow?  Prevent a lean spot right as the plate cracks open?  I never

messed with it beyond making sure it functioned... whatever jet was in there did whatever it did!

 

hth

 

t

 

Edited October 19, 2021 by TobyB

[John76]

8 hours ago, Mucci said:

 If the secondary idle jet doesn’t come on until the secondary starts to open at 2/3 throttle why is it called an idle jet?

Because it doesn't do anything until the secondary starts to open....therefore it sits "idle" ???

 

9 hours ago, Mucci said:

leaning out more at WOT

Float level??  Fuel pump pressure??   Not enough "squirt" from the accelerator pump??

[Mucci]

22 minutes ago, John76 said:

Because it doesn't do anything until the secondary starts to open....therefore it sits "idle" ???

Float level??  Fuel pump pressure??   Not enough "squirt" from the accelerator pump??

How would improper float height would cause a top end lean? I can understand this in motorcycle carbs where the mains are above the fuel line but the mains on these Webers are at the bottom of the bowl. Wouldn't I have to drain the entire bowl before starving the mains?

I don't have a fuel pressure gauge on the car unfortunately.

Accelerator pump squirt is only active for a moment when cracking the throttle correct? How would this produce high end lean condition?

[kbmb02]

8 minutes ago, Mucci said:

How would improper float height would cause a top end lean? I can understand this in motorcycle carbs where the mains are above the fuel line but the mains on these Webers are at the bottom of the bowl. Wouldn't I have to drain the entire bowl before starving the mains?

 

The magic of emulsion tubes should also be part of your reading material (float level impacts e-tube functionality, and thus the mixture).

 

More to consider: Are you noting the air density level at the time of your test(s)? Why? Because if the ambient temperature changes between tests (likewise dew point, to a lesser degree (I find)), you're adding another variable to your data. -KB

[percy]

10 minutes ago, kbmb02 said:

 

The magic of emulsion tubes should also be part of your reading material (float level impacts e-tube functionality, and thus the mixture).

 

More to consider: Are you noting the air density level at the time of your test(s)? Why? Because if the ambient temperature changes between tests (likewise dew point, to a lesser degree (I find)), you're adding another variable to your data. -KB

Took the words right off of my keypad.    Other integral considerations include ignition timing and camshaft/valve timing.

Edited October 19, 2021 by percy

[John76]

17 minutes ago, Mucci said:

How would improper float height would cause a top end lean?

 

The venturi sucks emulsified fuel from the top of the well. The air corrector jet controls the air, the float bowl level (and main jet) controls the fuel and the level in the well. Increasing the fuel level in the float will keep the fuel in the emulsion tube at the right level (to interact with the holes)  depending on the power of the venturi suck. Raising float level will richen the mixture,  lowering will lean it. Liquid (gas) will seek it's level as long as the main jet is somewhere below the surface in the float chamber .

It's the vacuum (low pressure) through the carb that changes the gas level between the float and the well.

 

35 minutes ago, Mucci said:

Accelerator pump squirt is only active for a moment when cracking the throttle correct?

 

Correct...however if it doesn't squirt enough before the secondary circuit catches up, you can get a lean skip.

 

Fuel pump pressure and flow rate are important to know. Under continuous WOT, your fuel pump may be unable to keep up with the demand.

 

John

PS: Just trying to add some thought to your issues. Hence the questions about your jets, timing and other mods.