Reading Spark Plugs

[tlap]

I am in the process of tuning my 32/36 Weber that is on a Cannon manifold, I would like some opinions about the look of these plugs. This picture was taken after my weekly commute to work, which is mostly highway driving. I do run premium fuel also.

They are in my L20 with about 2000 miles on the rebuild. The engine has L18 pistons with an open chamber U67 head that has been port matched, along with the runners and combustion chambers smoothed.

The Distributer is a matchbox.

I have installed a heated oxygen sensor to a narrow band air/fuel ratio gauge.

The AF gauge is indicating that there is one maybe two cylinders running a bit rich, as indicated by the #3. And maybe the #2 is a bit lean.

Why would there be such a difference in plugs from cyl. to cyl.?

and do you think that going to a slightly hotter plug in #3 would help

The Weber is jetted as follows....

Mixture screw - 2 turns out.

Acc. pump jet - .055

Pri. air - 170

Sec. air - 160

Pri. main - 150

Sec. main - 145

Pri. idle - .060

Sec. idle - .050

The AF gauge shows that at Idle, it runs "optimal" to "rich".

At cruise speed (65-70), no load, it is off scale "lean", but at a slight load it is "optimal".

A W.O.T it is "optimal" to "rich".

Thanks

[DISLEXICDIME]

I am in the process of tuning my 32/36 Weber that is on a Cannon manifold, I would like some opinions about the look of these plugs. This picture was taken after my weekly commute to work, which is mostly highway driving. I do run premium fuel also.

They are in my L20 with about 2000 miles on the rebuild. The engine has L18 pistons with an open chamber U67 head that has been port matched, along with the runners and combustion chambers smoothed.

The Distributer is a matchbox.

I have installed a heated oxygen sensor to a narrow band air/fuel ratio gauge.

The AF gauge is indicating that there is one maybe two cylinders running a bit rich, as indicated by the #3. And maybe the #2 is a bit lean.

Why would there be such a difference in plugs from cyl. to cyl.?

and do you think that going to a slightly hotter plug in #3 would help

The Weber is jetted as follows....

Mixture screw - 2 turns out.

Acc. pump jet - .055

Pri. air - 170

Sec. air - 160

Pri. main - 150

Sec. main - 145

Pri. idle - .060

Sec. idle - .050

The AF gauge shows that at Idle, it runs "optimal" to "rich".

At cruise speed (65-70), no load, it is off scale "lean", but at a slight load it is "optimal".

A W.O.T it is "optimal" to "rich".

Thanks

 

I dont think you can run a narrow band gauge with a wide band sensor. correct me if i am wrong.

Are these the first set of plug's this engine has had since the rebuild? If so you could have fouled the plug's a little breaking it in.

clean the plug's go out hammer on it hard turn the car off and coast to the side of the road. Pull the plug's and then read them. that will tell you if you are leaning out in your top end

[tlap]

DISLEX, These are the first plugs since the rebuild. I will put in a new set, along with a rotor and cap.

The gauge's manual states that a heated O2 sensor can be read from it. A three wire O2 sensor only puts out a 0-1V signal, and that is what the gauge reads. The other two wires are for the heater element.

Doing a plug chop from W.O.T would tell me what that portion of the carburetor's circuit is doing, and I will try that, but I do want all three circuits (idle, primary and secondary)working as good as possible.

Thanks

[DISLEXICDIME]

to really get the afr right you need a wide band 02. can you take a pic of the manifold ?

[tlap]

Here is the manifold.

As far as wide band vs narrow band goes, I do agree that you can get much more accurate readings with the WB. However I do also believe that a NB can, and does get you more information than just reading plugs or seat of the pants testing.

[racerx]

Why do you think they went EFI...you can never get carbs exactly right. Even if you get near perfect, one of your plugs will always be darker, lighter than the other. I think 2 turns out is too much. Maybe 1.5 turns.

[RoadRace]

were they used pistons? what type of ring? what was the top and 2nd ring gap? was the head rebuilt as well? new cam or used one? there are many questions that can be asked to diagnose a problem like this one.

 

But, i would like to know: 1)were these plugs new when with the engine? were they from the previous motor?

 

from what i can see, there appears to be heavy carbon on the #2 plug body, indicating the fuel is getting there and not being burnt correctly.

 

try 4 new plugs, B6ES, and report back.

[racerx]

This is a good article...but the best way is to not only drive it around but your throttle must be at WOT to get true reading. I've even read articles to take your car to a race track or open road (but you may get a ticket, going 80 mph or so). Do you see the parapgraph about being 2.5 turns, idle screw is too small if out less than 1.5 then too big or rich.

 

 

Carburetor Set Up and

LeanBest Idle Adjustment

Base line Settings

Speed Screw 1 to 1-1/2 turns

Mixture Screw 2 turns

Your settings with engine running

Speed Screw______________

Mixture Screw______________

It is important to follow all linkage and lever installation instructions. The number one and two reasons for tuning errors are

improper linkage installations and over tightened linkage nut, causing a binding in linkage assembly.

CALIBRATIONS MAY VARY DUE TO REGIONAL FUELS AND STATE OF ENGINE TUNE AND PERFORMANCE.

POOR RUNNING QUALITY DOES NOT MEAN A DEFECT IN THE CARBURETOR. AN ADVANTAGE OF THE WEBER

CARBURETOR IS ITS EASE OF ADJUSTMENT AND TUNING.

SET UP ADJUSTMENTS

Start set up by confirming carb base line settings. Do not depend on the factory delivered settings. Check them before the

carb is installed.

All settings are done with choke disengaged or warmed up so that the choke is fully opened and disengaged. This is done

on automatic choke carburetors by first opening the choke butterfly by hand and inserting a wood block or wedge of some

kind to hold open while the linkage is cycled (linkage operated through its full movement ) to clear the choke cam. (You

will hear a metallic click as the cam is released. You can check the fast Idle screw under the choke assembly to confirm

that it is not in contact with the choke fast idle cam.)

Set the Idle stop screw (speed screw see fig 1) by backing out the Idle speed screw until it is not in contact with the

throttle stop lever. Cycle the linkage again to be sure that the linkage comes to close without any assistance. (Checking

for linkage bind) Now bring screw back into contact with the lever and continue to open or screwing in 1 turn no more

than 11/2 turns.

Set the mixture screw (see Fig 1) by first screwing in until the screw stops, bottoms out. DO NOT FORCE OR BIND AS

THIS WILL CAUSE DAMAGE TO THE SCREW AND IT’S SEAT IN THE BODY OF CARBURETOR. Back out the

screw 2 full turns.

TUNING

1. BE SURE TO FOLLOW THE NEXT INSTRUCTIONS IN THE PROPER SEQUENCE, DEVIATION WILL CAUSE

THE CARBURETOR TO NOT FUNCTION TO ITS IDEAL SPECIFICATIONS AND MAY NOT PROVIDE THE

PERFORMANCE AND FUEL ECONOMY AS DESIGNED.

2. Start the engine, the engine will run very slowly more like a tractor. As long as the engine stays running idle speed

is not important at this point.

3. The first thing to do is not set up the idle speed, but to set the Idle mixture screw to lean best idle setting. First,

turn in the mixture screw until the engine dies or runs worse, then back out the screw (recommend turning ¼ to ½

turn at a time). The engine should pick up speed and begin to smooth out. Back out ½ turn more, or until the screw

does nothing or runs worse then turn back to the point where it ran its best.

4. Use your ear, not a scope or tuning instruments at this point. You want to tune the engine by sound. Adjust to

best, fastest and smoothest running point.

Carburetor Set Up and

LeanBest Idle Adjustment

5. Now that the mixture screw is at its best running location, you can adjust the Idle speed the screw. The screw will

be sensitive and should only take ¼ to ½ turns to achieve the idle speed you like.

6. Check and set idle to your driving preference. Put the car in gear and apply slight load, (AC on) and set the Idle

as you like it. Don’t set it too high, as this will cause causes excessive clutch and brake wear. The Idle only needs to

be 7 to 900 RPM with light load or AC on.

7. Recheck timing and vacuum hook ups. Recheck mixture screw to lean best idle again. If all is still best and

smoothest idle then confirm and note the final settings.

8. To confirm settings with the engine running. Start by screwing in the mixture screw and count the number of turns

it takes to bottom out and note if the engine dies. If Idle Mixture screws are with in ½ turn of base line setting then all

is well and have fun. Also check the speed screw and note how many total turns from initial contact. You may have

opened (turned in) the speed screw. Your final setting should be under 2 full turns. Reset the screws (back in) to the

best final settings (Per your notes) and go on a test drive and have fun. If the settings are other than described then

you may want to recalibrate the Idle circuit (low speed circuit) to your engines needs. This is done by following the

rule of thumb BELOW.

Simple Rules for low speed calibration

If the mixture screw is more than 21/2 turns out turns then the Idle jet is too lean (too Small). When the mixture screw is

less than 11/2 then the Idle jet is too rich (too large). These assumptions are based on the fact that the speed screw

setting is not opened more than 11/2 turns. If the speed screw has to be opened 2 or more turns then this is also an

indication of a lean condition usually requiring greater change. At times it may appear to be showing signs of richness or

flooding it is really a lean condition. See pictures and notes in the tech 2 article supplied in the kit instructions, view and

please understand the need to keep throttle plate as near to closed as possible so as not to prematurely expose the

transition holes. This is what causes the visible rich condition, and confirms the need to increase the jet size. JET KITS

are available if needed.

EXAMPLE

With the speed screw set at no more than two (2) turns in after contact with the stop lever; and the best idle occurring with

the mixture screw set at 3 turns from bottom, indicates the need for a larger Idle jet. Achieving the best idle at under 2

turns indicates the need for a smaller idle jet.

The secret to understanding the critical nature of the carburetor set up and the advantages of a WEBER over other

carburetors is the Idle circuit. Referred to as the low speed circuit by Weber, this circuit is responsible for 80% of the

driving operation. This is the reason that the Weber should give a fuel economy improvement over most factory carbs

along with significant performance gains. In the worst case you should not see a significant fuel economy loss over stock,

while improving HP & Drivability.

The Weber Carburetor is a sequentially timed device to the motor like the distributor. Time taken in the setup will provide

more fun later

Primary Venturi Primary Emulsion Tube

Secondary Venturi Secondary Emulsion Tube

Primary Auxiliary Venturi Primary Idle Jet

Secondary Auxiliary Venturi Secondary Idle Jet

Primary Main Jet Pump Jet

Secondary Main Jet Needle Valve

Primary Air Corrector Jet Float Measurement

Secondary Air Corrector Jet

WEBER

16

1.60 mm

1.40 mm 2.00 mm

1.65 mm 38.50 mm

3.50 mm .50 mm

1.37 mm .55 mm

27 mm F50

3.50 mm .60 mm

WEBER CARBURETORS

32/36 DFEV 22680.070

ORIGINAL SETTINGS

26 mm F66

WEBER

KEY NO. QTY DESCRIPTION PART NUMBER KEY NO. QTY DESCRIPTION PART NUMBER

1 1 Cover Assembly 31716.221 48 1 Spring 47600.141

2 4 Stud 64955.002 49 1 Cover 32384.022

3 5 Screw 64700.005 50 1 Screw 64595.005

4 1 Gasket 41705.034 51 1 Screw Plug 61015.003

5 1 Primary Air Jet 77201* 52 1 Screw 64700.015

5-A 1 Secondary Air Jet 77201* 53 1 Gasket 41640.005

6 1 Pump Delivery Valve 64290.017 54 1 Auto-choke Thermo Assy 57804.076

7 1 Primary Emulsion Tube 61440.220 55 1 Thermostat Ring 52135.006

7-A 1 Second Emulsion Tube 61440.216 56 1 Gasket 41555.001

8 2 Gasket 41530.012 57 1 Screw 64615.001

9 1 Accelerating Pump Jet 76211* 58 1 Gasket 41530.002

10 1 Power Valve 57804.096 59 1 Water Chamber 32444.010

11 1 Needle Valve 79519.200 60 1 Choke Shaft 10085.040

12 1 Float Pin 52000.015 61 3 Screw 64700.007

13 1 Float 41030.022 62 1 Spring 58000.018

14 1 Primary Idling Jet 74403* 63 1 Washer 55525.003

14-A 1 Secondary Idling Jet 74403* 64 1 Nut 34715.016

15 2 Jet Holder 52570.005 65 2 Screw 64700.023

16 1 Carburetor Body Not Supplied 66 1 Plate 52130.012

17 1 Secondary Lever 45032.013 67 1 Washer 55555.029

18 1 Washer 55510.046 68 1 Screw 64750.028

19 1 Washer 55525.001 69 1 Spring 47600.007

20 1 Nut 34705.001 70 1 Gasket 41565.008

21 1 Spring 47605.010 71 1 Pump Cover 32486.034

22 1 Loose Lever 45069.006 72 4 Screw 64700.004

23 1 Washer 55510.061 73 1 Diaphragm 47407.016

24 1 Throttle Lever 45041.097 74 1 Spring 47600.107

25 1 Washer 55520.002 75 4 Screw 64520.023

26 1 Nut 34715.014 76 1 Primary Throttle Plate 64005.090

27 1 Bushing 12775.006 77 1 Primary Shaft 10015.484

28 1 Lever Assembly 45041.029 78 1 Secondary Shaft 10015.413

29 1 Lever 45039.022 79 1 Secondary Throttle Plate 64005.034

30 1 Spring 47600.073 80 1 Primary Main Jet 73801*

31 1 Screw 64625.006 80-A 1 Secondary Main Jet 73801*

32 1 Screw 64595.005 81 1 Gasket 41530.013

33 1 Spring 47610.012 85 1 Power Valve Assy 64235.016

34 1 Washer 55555.016 83 1 Gasket 41535.015

35 1 Lever 45041.047 84 3 Screw 64700.007

36 1 Screw 64590.004 85 1 Strainer Plug 61002.018

37 1 Spring 47600.007 86 1 Ring 10140.501

38 1 Lever 45039.049 88 1 Choke Shaft 10020.214

39 1 Screw 64700.014 89 2 Screw 64525.003

40 1 Bushing 12765.042 90 1 Plug 61070.002

41 1 Washer 55530.005 91 1 Plate 52135.018

42 1 Rod 61280.042 92 1 Strainer 37022.010

43 1 Washer 55510.003 93 2 Choke Plate 64010.006

44 1 Choke Lever 45034.063 94 3 Screw 64615.009

45 1 Spring 47610.083 95 1 Pump Needle 64900.001

46 1 Auto-choke Body Assy Not Supplied 96 3 Washer 55510.038

47 1 Diaphragm 47407.080 97 2 Auxiliary Venturi 71110*

1 Gasket Set 92.0105.05 99 1 Electric Choke 57804.332J

1 Repair Kit 92.1130.05 * Calibrated Parts

32/36 DFEV 22680.070

WEBER CARBURETOR PARTS LIST

WEBER

17

WEBER

[tlap]

RoadRace, The pistons were new L18's, the rings were new and gapped to the spec in the Datsun book. The valves were new, 3 angle valve job, new guids and head surfaced. However the cam is the one that I got with this car. The shop that did all the machine work looked at it and said that it checked out good. I do not know what grind it has though.

I do have new plugs, rotor and cap on order.

Racerx, maybe you have it. Is this just the "nature of the beast"? I do have those instructions too. My mixture screw is at 2 turns, so I am thinking that the idle jet is probably OK.

When you say that to get true readings your throttle must be at WOT, wouldnt that only give you an indication about how it is jetted in the secondary circuit?

Maybe I am trying to pick the fly shit out of the pepper here, but I would like to have it run as well as possible through out the power range. Perhaps this is as good as it gets?

Oh one more piece of info, the compression is 220 psi in all four cylinders.

[racerx]

It's better to check with new plugs, you can read them better. Well sounded like you wanted to get true reading so I suggested drive around town and at WOT, so that you can read at various ranges. Yeh, I've had these 32/36 in like 5 cars and it's almost impossible to get true readings since they are carburator. Had them in 2 Datsun wagons, 1 sedan, Capri and a 1975 Toyota Celica. The celica I had a hard time getting the spark plug nice and brown. Tried different plugs, timing less/more, messed with the JETs and it was still not up to par. The only thing I did not do was mess with the air JETS...BTW just curious, did you adjust your 32/36 using a vacuum gauge, by turns or by ear. I think the vacuum gauge adjustment is probably better, where you set the idle mixture at base, hook up a vacuum gauge at vacuum port (intake-not carb) and turn the idle screw till you max. your vacuum?

[tlap]

racerX, I set the idle with a four gas smog machine, then compared that to my AF gauge.

Since you have used these carbs so much, do you think that the only way to achive a more consistant and uniform AF ratio in all four cylinders is EFI? Or is there better tunability with twin SU's?

[racerx]

Well that's just been my experience with carbs. To trully fine tune carbs, eventhough retailers will say they are jetted already, you have to have all types of JETS. This means you will have to take the top off and mess with the air JETS, then change the gasket and so on. Which also means you have to drive it, log your JET size, drive it again, change your JETS and when you change one you have to change the other.

Even then your spark plugs will not all be exactly the same color because compression will be different, give or take a few, with each cylinder. The other thing that can affect the color is timing, condition of the engine (new/old), plug type (hot/cold), how much you gap. On the otherhand an EFI system, have sensors like MAP, TPS and OS that monitors air, fuel, pressure and even weather so that it callibrates itself. Whereas, carbs don't have these, unless you hook up OS sensors like you did but that's all it will do. It will just let you know that you are running rich/lean.

 

Plus these carbs are not meant to run clean like the stock ones because they are performance types. The stock ones like Aisan carbs were meant for passing smog and economy. I've never seen spark plugs where they are all the same color, specially carb types of cars. I've seen like colors on my 91 GT mustang, then again that's an EFI.

 

BTW how did you get 210 PSI with compression? I am not sure about SUs, never ran them. I've never messed with them. I've had exp. with 4 bbl (65 Mustang) and 2 bbl (my 65 Falcon), or the 32/36 webber

[tlap]

I have accumulated a selection of jets so far. It is kinda fun dialing it in as well as it can be.

I check compression with a compression kit, cold, throttle fully open, cycle the strokes until the gauge indicates its peak pressure, And all four cylinders are consistently at 210-220 psi.

From what I have read and what the machine shop figured, that the smaller dish (4.36cc) in the L18 pistons, L20 bore size (85.5mm), the stroke of the L20 (3.39")and the open chamber head volume of about(44.5cc), was in the vicinity of 9.77:1. Does that sound about right?

[RoadRace]

9.77:1 is close. i had the same piston and 36cc and i got 10.07:1 - but i cc'd my piston volume measured exactly 1" below the deck height, then i subtract the "perfect" 1" of volume from the cylinder from the actual number i recorded with my burette to get the 'true' number. i would suspect you are closer to 9.4 - either way, its totally fine.

 

but, like it has been mentioned, you should post the vacuum numbers and timing before and after vacuum advance as well as total timing. flame travel is a funny thing and if your timing is out or you have less than adequate fuel - that you may not even notice - then one or 2 cylinders may not burn properly. the plug could be wrong as well. it is not uncommon to get a bad plug in a box of 10.

 

doing a 'plug-chop' from full throttle is a great way to get a reading - but you have to look at the grounding strap and the exposed metal ring or base for temp, mixture and flame travel, then the center electrode to determine timing accuracy. doing a plug chop with brand new plugs is harder to read, its best to put a few miles on them first.

[datzenmike]

L20B with stock bore and 4.36cc L18 pistons with 45.3cc open chamber head would have a compression ratio of a little over 9.25