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Tuning 40 DCOE Weber 151 on an L24

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Just did some tuning with DR240z. We settled on this:

 

Engine:

Block: L24

Head: Maxima N47

Cam: ~280 duration 0.48" lift

 

Transmission and Differential: stock 4 speed 3.545

 

Carbs:

40DCOE151 (3)

30mm Choke

Fuel Height: ~30mm down from top of body

Idle Jet: 55F9

Enrichment Screws: 2.25 turns

Emulsion Tube: F11

Air: 70

Main: 120 

 

A/F Ratios:

Idle: 13.5

60mph cruise on flat: 15.6

70mph cruise on flat: 14.5

 

WOT runs 12-13

 

After setting fuel level to 30mm down, we first tuned by selecting a jet for cruise at 60mph that was near stoich (~15:1) and could be dialed to slightly rich for a smooth idle(~13:1).  The 55F11 did the trick.

 

We then checked the effect of the main on cruise. The car had a 115 main when the fuel level was 25mm down. We tried a 125mm main with the fuel now at 30mm down but it dropped the 70mph cruise to 12.5 w/o doing much to the 60mph cruise. We settled on the 120mm.

 

 

The car runs crisp with no bogging nor rich fuel smell. 

 

Nice even mocha coloured plugs to boot.  No popping or backfiring under load, over run, or at any rpm.

 

Success.  

 

 

 

post-6852-0-10072900-1439166760.jpg

Not too sure if this is important to note: Set up was carried out at 1250 feet above sea level and temp was 70 F

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Reviving this thread as I'm a few years behind y'all...

L28/e88 combo with bone stock, albeit fresh, internals.  

DCOE 42.

135 Main

165 Air

55F2 idle

F15 emulsion

45 Accelerator

? Choke (haven't measured them)

50mm slide in velocity stacks

 

Car starts and idles great, but I'm pig rich at WOT (10:1), looking good at idle and cruising idle (13.5:1), and wildly lean at tip in (18:1).  

My guess is a previous owner went rich across the board to mask the lean tip in as much as possible.  I'm trying to get the AFRs better step by step and my question is whether success has been had to bigger acceleration jets?  

Leaning out my idle jet (F8 to F2) improved my driving idle, and accentuated my tip in lean spot.  

Waiting on jets to play some more...

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Reviving this thread as I'm a few years behind y'all...
L28/e88 combo with bone stock, albeit fresh, internals.  
DCOE 42.
135 Main
165 Air
55F2 idle
F15 emulsion
45 Accelerator
? Choke (haven't measured them)
50mm slide in velocity stacks
 
Car starts and idles great, but I'm pig rich at WOT (10:1), looking good at idle and cruising idle (13.5:1), and wildly lean at tip in (18:1).  
My guess is a previous owner went rich across the board to mask the lean tip in as much as possible.  I'm trying to get the AFRs better step by step and my question is whether success has been had to bigger acceleration jets?  
Leaning out my idle jet (F8 to F2) improved my driving idle, and accentuated my tip in lean spot.  
Waiting on jets to play some more...

What setup are you using to measure A/f ratio?

Thx!


Sent from my iPhone using Tapatalk

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Tip in means when I accelerate.

I'm using an innovates AF in the header and a mech gauge to read.

I have 130 and 120 jets on the way given my 10:1 at WOT.

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Chokes are an unknown, so I assume the stock given 42 chokes are like unicorns.

When I accelerate from cruising it goes

13.5:1 cruise -> 18:1 for a bit -> 10:1 on mains.

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take a choke out, it'll either be marked or you measure it.

assuming you're opening the throttle reasonably slowly, your 18:1 is on the progression holes or between the progression holes and the main jets.
progression holes are supplied by the idle jets.

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Opening slowly or mashing it results in the same spike in AFR and engine shudder. 

Because I can't actually change my chokes I haven't been bothered by what they are.  Are possible solutions different depending on the size of the chokes?  E.g. if a choke were smaller I'd look at my idle jet vs. looking at my main jet if I had larger choke?

Sorry if this is a dumb question, but I'm learning here.

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Usually there is a lean blip then a rich drop. It is hard to tune out.

Make sure your fuel levels are all the same across the 3 carbs. 30 to 27mm down from the jet bridge works nicely.  Aim for all 3 to be a 29mm as a staring point.

 

 

Edited by 240260280

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Opening slowly or mashing it results in the same spike in AFR and engine shudder.  Because I can't actually change my chokes I haven't been bothered by what they are.  Are possible solutions different depending on the size of the chokes?  E.g. if a choke were smaller I'd look at my idle jet vs. looking at my main jet if I had larger choke?

Sorry if this is a dumb question, but I'm learning here.

 

 

yes. the choke size determines the air speed and suction at the main jet outlet, which determines when the main jet comes in (in part). so with a big choke, you can run out of progression holes before the main jet kicks in and it goes lean and the answer is to fit smaller chokes or possibly add progression holes or if its marginal you can get away with just larger idle jets and make the progression phase richer to cover the transition to main jets.

 

with small chokes, you're probably just lean through the progression phase and bigger idle jets/richer idle holder wil fix it (and you turn down the idle screw so its not too rich at idle).

 

why do you say your chokes can't be changed?

 

 

 

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Ah right, the 42 DCOEs! I still think it would be helpful to have one out and measure it. Perhaps after you've checked the float levels.

Is there a gap between the two progression holes, or will the throttle plate start uncovering the 2nd as soon as it finishes the first?

Do you think you can position thr throttle pedal at the problem point while the car is stationary?

You could get someone to look at the progression holes for where the throttle plate is when the problem occurs. after the 1st hole or after the 2nd.

 

 

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I have someone that can help with watching the progression holes and butterfly. They are spaced, but not a lot.

I have new gaskets on the way so I can measure when I swap those in. I'd like to eliminate the chance of a vacuum leak.

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