Fine Tuning Weber 32/36 with Wideband

[Mucci]

Thanks for the info folks. Ok here's the full spec list currently:

Car
1975 2002

Location

Santa Cruz, CA (sea level) - 60F

Motor
Stock internals. Valve clearance set to .007.
Long tube headers to 2.25" exhaust with IE muffler. No resonator. 

Ignition

New STI plug wires with NGK BP7ES plugs.

Pertronix ignition
Flamethrower coil

 

Advance per RPM:
12 @ 1000
29 @ 1500

31 @ 2000

36 @ 2500
42 @ 2700+

Carburetor
Weber 32/36 DGEV

P. idle: 65
P. main: 140

P. air corrector: 170

 

S. idle: 60

S. main: 145

S. air corrector: 160

Mixture screw 2 turns out.

AFR

 

Idle: 12.5

Low RPM / Low Throttle (cruise): 13.5 - 14.2

1/2 throttle Acceleration: 12.8-13.8

WOT / Low RPM: 15.0-16.5

WOT / High RPM: 15.0-17.5

 

 

[Doug Riparetti]

On 10/17/2021 at 10:21 PM, Mucci said:

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?

 

What motorcycle carbs were you tuning on? I'm running 44mm Mikuni VM series on my S14.

[John76]

Thanks Mucci.

Your info is important to the "Weber Wizards" on the this forum.

 

Just a few more details would also be helpful:

 

Float: Plastic or Brass?  What is the current setting? (Plastic = 35mm, Brass = 41mm)

Distributor: Stock '75 w/ vacuum advance and retard?  How do you have it "plumbed"?

Fuel pump: Stock or electric?  Using fuel return valve?

Spark plugs: How do those BP7s look?  With a stock engine (low compression) these may be too cold.

 

John

 

 

[Mucci]

3 hours ago, Doug Riparetti said:

What motorcycle carbs were you tuning on? I'm running 44mm Mikuni VM series on my S14.

They were on actual motorcycles. Mikunis, Keihins, Dellortos...

[Mucci]

2 hours ago, John76 said:

Thanks Mucci.

Your info is important to the "Weber Wizards" on the this forum.

 

Just a few more details would also be helpful:

 

Float: Plastic or Brass?  What is the current setting? (Plastic = 35mm, Brass = 41mm)

Distributor: Stock '75 w/ vacuum advance and retard?  How do you have it "plumbed"?

Fuel pump: Stock or electric?  Using fuel return valve?

Spark plugs: How do those BP7s look?  With a stock engine (low compression) these may be too cold.

 

John

 

 

- Brass floats. I think I set them to 40mm but that was a year ago when I rebuilt the carb so I should check again. I remember I was told by a Weber tech back then to set the float height 2-3deg down from horizontal to account for the change in buoyancy of modern fuel. Not sure what that equates to in mm. 

- Stock dizzy, Bosch 003. Vacuum advance diaphragm plumbed to the vac port at the base of the Weber. No vacuum retard.

- Stock fuel pump. Not sure what you mean by return valve. There's a return line that runs along the drivers frame rail. 

 

- Plugs may actually be BP6ES, I'll have to check. I had 2 empty boxes and couldn't remember which went in the car. I've had a lot of motorcycles that ran BP 6 and 7 plugs so I've got stacks of both. 

Edited October 20, 2021 by Mucci

[Doug Riparetti]

44 minutes ago, Mucci said:

They were on actual motorcycles. Mikunis, Keihins, Dellortos...

?

[TobyB]

Quote

 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?

Yes, but as John kinda said above, the Weber draws the fuel 'up and over' the top of the

jet passageway.  (I think of it as a 'stack', from the sidedrafts)

 

So the amount of fuel in the bowl directly affects how much 'pull' it takes to get the main circuit

to deliver.  And as Ken said, the emulsion tubes start to interact earlier if the fuel level's lower, too.

 

Go richer on the secondary fuel jet, and if you don't get an immediate richer response,

then yes, start looking at fuel supply.  You don't say what needle valve- I've never seen this

be a real restriction, but I guess a really small one with really low fuel pressure could cause this.

 

Don't fart with the emulsions-  yet.  You want to get the fuel jets closer, and the air correctors

roughed in, and THEN the emulsions can help with bumps in the curve.  Frustratingly, the emulsions

may change the air correctors, but by that point, you'll be good at dialling those.

 

Your half- throttle mixture looks really good- this is where I'd love to know if the secondary's 

involved with it or not...

 

t

 

[John76]

2 hours ago, TobyB said:

Your half- throttle mixture looks really good- this is where I'd love to know if the secondary's 

involved with it or not...

 

The "mysterious" idle jet in the secondary flows when the secondary starts to open. This gives a little boost as the primary loses it's influence as the secondary starts to contribute. This is why it might be useful to know when this happens.

As Tom ('76mintgrun'02) noted, you can see the transition point with your AFR.

Try switching your idle jets:  Put the 60 in the primary and the 65 in the secondary and see if that leans out the idle a bit and fattens up the top end when the secondary kicks in.

[TobyB]

yeah, I suppose that's where 'transition' jet's more accurate, huh?

 

I have to admit, I've never looked at the bore drillings for the secondary transitions,

but they are critical for the primary.  If I can get my butt off the internet,

I'll go take a look at one!

 

In my mental model, by the time the secondary's starting to open in real driving

conditions, there's enough airflow to pull from the mains.  BUT if the secondary's

JUST starting to open slowly (you're driving up a grade that's getting a bit steeper)

then without that transition passage, the secondary would be a big air leak, and a lean spot.

 

t

totally agreeing with John.

[Mucci]

11 hours ago, John76 said:

 

The "mysterious" idle jet in the secondary flows when the secondary starts to open. This gives a little boost as the primary loses it's influence as the secondary starts to contribute. This is why it might be useful to know when this happens.

As Tom ('76mintgrun'02) noted, you can see the transition point with your AFR.

Try switching your idle jets:  Put the 60 in the primary and the 65 in the secondary and see if that leans out the idle a bit and fattens up the top end when the secondary kicks in.

Unfortunately it seems that the primary idle jet wants to be fatter if anything. With the 65 my mixture screw is right at 2 turns out in order to get the highest idle. On either side of 12.5 the idle speed drops. I had the 60 in there before and the mixture screw and throttle stop screw both had to go beyond Weber's spec in order to hit highest idle and a smooth idle RPM around 900. 

That's why I was asking about the secondary idle jet's influence. If it was in fact influencing idle I was thinking I could increase that jet, turn the idle screw in a bit so it wasn't on the 2-turn cusp, and hopefully fatten up the secondary / top end. Only reason I haven't tried it is because Weber doesn't give you a 70 idle jet in the kit. 

Edited October 20, 2021 by Mucci

[John76]

1 hour ago, Mucci said:

I had the 60 in there before and the mixture screw and throttle stop screw both had to go beyond Weber's spec in order to hit highest idle and a smooth idle RPM around 900. 

 

Hummm...I have the same engine ('76 CA) but the stock distributor is Bosch 0 231 176 059 (w/ vac advance and retard).

I have the vac advance connected to manifold vacuum and no vac retard.

A 60 primary idle jet, 8 degrees of advance @ 900 rpm results in 20"Hg of manifold vacuum. Smooth idle and transition.

Looking at your settings, you might have too much initial advance and total advance.

My idle mixture screw is well within the suggested range...1 1/2 turns out, and the idle set screw is only turned in a tad over turn.

Do you have a vacuum gauge?

This thread has pushed me over the top....I'm getting a AFR!!!   Good stuff.

 

['76mintgrün'02]

Which emulsion tubes do you have, Mucci?  

 

The c.d. recipe uses f50 tubes (and so do I), which I believe are the most common ones.

 

You don't necessarily need a fatter idle jet, if you go smaller on the air corrector.  I think mine is a 160 on the primary side, to lean it out a bit from his 145.  Your 170 seems large.  12.5 is where mine idles best.  It's smooth down into the 700's, but it's set around 800 rpm, with 10 degrees advance at idle.

 

c.d. jetting for comparison --

 

PRIMARY

idle 60

main 140

air correction 145

SECONDARY

idle 55

main 170

air correction 175

 

P. idle: 65
P. main: 140

P. air corrector: 170

 

S. idle: 60

S. main: 145

S. air corrector: 160

 

17 minutes ago, John76 said:

This thread has pushed me over the top....I'm getting a AFR!!! 

 

You'll love having an AFR gauge to watch, John.  I'd suggest getting one with a needle.  They're a little harder to come by than the LED style, but there are a few to choose from.  Mine's an earlier INNOVATE model... which pairs nicely with our INNOVA timing lights.

 

Speaking of timing, I don't think 12 is too much at idle, but 42 seems like more than you'll need (want?) up top. 

 

Speaking of vacuum advance, pulling it off of manifold vacuum will put your idle advance up another 12 degrees.  I choose to use ported... but this thread is about jetting carburetors and we don't need to type about manifold vs ported sources again.

 

Tom

[Son of Marty]

17 hours ago, Mucci said:

- Brass floats. I think I set them to 40mm but that was a year ago when I rebuilt the carb so I should check again. I remember I was told by a Weber tech back then to set the float height 2-3deg down from horizontal to account for the change in buoyancy of modern fuel. Not sure what that equates to in mm. 

 

The specific gravity of gasoline must be between 0.720 and 0.770 to be sold. When adding enough ethanol to the mix to slide out of this range you'd need to be using around 80% of ethanol in the mixture, so the long and short of this is no need to adjust the float level for new age gasoline. 

[Mucci]

4 hours ago, John76 said:

 

Hummm...I have the same engine ('76 CA) but the stock distributor is Bosch 0 231 176 059 (w/ vac advance and retard).

I have the vac advance connected to manifold vacuum and no vac retard.

A 60 primary idle jet, 8 degrees of advance @ 900 rpm results in 20"Hg of manifold vacuum. Smooth idle and transition.

Looking at your settings, you might have too much initial advance and total advance.

My idle mixture screw is well within the suggested range...1 1/2 turns out, and the idle set screw is only turned in a tad over turn.

Do you have a vacuum gauge?

This thread has pushed me over the top....I'm getting a AFR!!!   Good stuff.

 

Unfortunately I don't have a vacuum gauge, only pressure gauges.

According to the blue book all my timing figures are within spec, although the 42 total advance is at the high end of the spec (38-42 degrees). I can try to dial a few degrees out of it. If my timing was too advanced how would that produce a lean condition up top? Wouldn't I experience some kind of pinging, power loss, terrible noises etc.?

 

 

4 hours ago, '76mintgrün'02 said:

Which emulsion tubes do you have, Mucci?  

 

The c.d. recipe uses f50 tubes (and so do I), which I believe are the most common ones.

 

You don't necessarily need a fatter idle jet, if you go smaller on the air corrector.  I think mine is a 160 on the primary side, to lean it out a bit from his 145.  Your 170 seems large.  12.5 is where mine idles best.  It's smooth down into the 700's, but it's set around 800 rpm, with 10 degrees advance at idle.

 

c.d. jetting for comparison --

 

PRIMARY

idle 60

main 140

air correction 145

SECONDARY

idle 55

main 170

air correction 175

 

P. idle: 65
P. main: 140

P. air corrector: 170

 

S. idle: 60

S. main: 145

S. air corrector: 160

 

 

You'll love having an AFR gauge to watch, John.  I'd suggest getting one with a needle.  They're a little harder to come by than the LED style, but there are a few to choose from.  Mine's an earlier INNOVATE model... which pairs nicely with our INNOVA timing lights.

 

Speaking of timing, I don't think 12 is too much at idle, but 42 seems like more than you'll need (want?) up top. 

 

Speaking of vacuum advance, pulling it off of manifold vacuum will put your idle advance up another 12 degrees.  I choose to use ported... but this thread is about jetting carburetors and we don't need to type about manifold vs ported sources again.

 

Tom

CD's figures are with a plugged secondary enrichment circuit so those numbers aren't really apples to apples unless I was to do that. 

I haven't changed the emulsion tubes so I assume it's the F-50s according to this:



 

 

3 hours ago, Son of Marty said:

The specific gravity of gasoline must be between 0.720 and 0.770 to be sold. When adding enough ethanol to the mix to slide out of this range you'd need to be using around 80% of ethanol in the mixture, so the long and short of this is no need to adjust the float level for new age gasoline. 

I'm just relaying what the engineer at Weber told me. He seemed very well versed in the 32/36. He even developed the sync-link. 

Edited October 20, 2021 by Mucci

[TobyB]

I just got in from the shed, and boy, are my arms sore...

 

errr....

 

Yep, the secondary 'idle' jet is indeed transition enrichment-

two holes well above the resting 'closed' position of the plate.

So if you got a transitional stumble when the secondary just started to open,

you'd go bigger on the secondary 'idle' jet.

 

t