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Tuning 40 DCOE Weber 151 on an L24

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I should be ok. The stoichiometric point of E10 is around 14.1:1 but the AFR meter normalizes what it measures to the stoich point of pure gasoline (14.7:1) since it calculates based on lambda (measured AFR = pure gas AFR * lambda). If I can lean it out a bit more, I'll be happy, and so will my wallet! :)

Oh yes, I forget that you are paying Bay Area gas prices. We are about 25cents under Sacramento...

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Oh yes, I forget that you are paying Bay Area gas prices. We are about 25cents under Sacramento...

Lucky bastard... LOL

We finally dipped under $4/gal recently.

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Guys,

still following this thread-even if I'm a Mikuni guy-LOL

I have contacted mr. Franck and he responded. I have never been able to get into Sidedraft Central Yahoo group-which was mandatory if I was going to be part of this experiment. I have resorted to getting a Yahoo e-mail account to see if that helps.

keith wrote me saying that I might benefit from the tubes if my car did not pass the F.I. test-you guys might have touched on this in this thread. I'd say I am border line in that aspect. I have been reading the last few posts and it sounds like I am where you are as far as a slight hesistation during hard tip-in at lower rpms. No coughing, sputtering, spitting-just a millisecond of hesistaion, so maybe i'm at a pretty good point. At higher RPMS, above 3500, there is no hesitation.

I have tried quite a few things, but don't know if I have ever completely gotten rid of that slight studder. Other than that, these carbs have really been wonderful. I am going to put some fresh needle&seats in the floats so I know everything is good, and i am going to take to the dyno!

This weekend I even played with valve timing to see if that would change anything concerning hard tip-in at lower rpms-it didn't. I did quite a swing on the cam timing and basically put it back where it was-slightly advanced.

I have noticed watching my AFR's that WOT AFR is dictated by when hard tip-in occurs. If I stomp it at 2500rpm the AFR's look super rich for a while thru the rpms before getting to the 13 range. If I start out at a higher rpm the AFR's look much more optimum thru the remaing rpm range.

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Just to add another data point to this thread:

My good friend has a 510 with rebuild L16 motor and dual DCOE40 side drafts with 32mm chokes. It came with 135 main jets.... and fuel-fouls the plugs. I have not had a chance to run with the O2 sniffer.

The L16 per chamber volume is the same and an L24 so carb sizing/jetting should be similar.

To recap:

L16 DCOE40 32mm Choke 135main Pig Rich ~ 7-8 AFR (Estimated)

L24 DCOE40 30mm Choke 125main Rich ~ 10-11 AFR (Measured)

L24 DCOE40 30mm Choke 120main Rich ~ 11-12 AFR (Estimated.. will be measured Spring 2013)

L24 DCOE40 30mm Choke 115main TBA ~ 12-13 AFR (Planned for Spring 2013)

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Just to add another data point to this thread:

My good friend has a 510 with rebuild L16 motor and dual DCOE40 side drafts with 32mm chokes. It came with 135 main jets.... and fuel-fouls the plugs. I have not had a chance to run with the O2 sniffer.

The L16 per chamber volume is the same and an L24 so carb sizing/jetting should be similar.

To recap:

L16 DCOE40 32mm Choke 135main Pig Rich ~ 7-8 AFR (Estimated)

L24 DCOE40 30mm Choke 125main Rich ~ 10-11 AFR (Measured)

L24 DCOE40 30mm Choke 120main Rich ~ 11-12 AFR (Estimated.. will be measured Spring 2013)

L24 DCOE40 30mm Choke 115main TBA ~ 12-13 AFR (Planned for Spring 2013)

Phil,

I just ran my L24 today with 120 mains (40DCOE with 30mm choke). Saw about 12:1 on AFR meter when I was looking. It was fairly cold out though, so it will be richer in warmer temps. I may go with 115s but it runs so well, I'm not in a hurry. ;)

I'd imagine at 7-8AFR, that 510 would be billowing black smoke out the exhaust pipe.

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yup... the plugs would foul after ~ 25km and black smoke. I had to give my friend new plugs to get home. He lives ~ 25km from my place and decided to take a drive over on Sunday. He barely made it home.

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Well, I'm doing it. I found a guy in England who is restoring a Maserati 3500 which uses a pair of 42DCOE 8, which I have three of. We agreed on a price that will give him three of his original carburetors and will get me three brand new 45DCOE 152's. So my tuning will begin anew. I would imagine, I can just transfer over the jetting I have and if my chokes (32mm) are the same, I should be running pretty close to the same.

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Well, I'm doing it. I found a guy in England who is restoring a Maserati 3500 which uses a pair of 42DCOE 8, which I have three of. We agreed on a price that will give him three of his original carburetors and will get me three brand new 45DCOE 152's. So my tuning will begin anew. I would imagine, I can just transfer over the jetting I have and if my chokes (32mm) are the same, I should be running pretty close to the same.

Nice, Rob! Keep us updated.

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Not sure about the equivalence of choke size with different carb sizes.

Check the file attached below, given by Duragg on HBZ.

The only exception would be at 32mm according to this chart so your comment may still apply LOL

post-15411-14150821265185_thumb.jpg

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Last week, I replaced the custom 100 air jets from the O3 etube with 140s. This flatlined my AFR trace at WOT! No more getting richer as rpms climb. This did make low-rpm transition a bit leaner but I'll be tuning that out with the hypojets, which control low-speed, low-throttle opening operation.

Next plan:

- Smaller hypojets, either the H20 or H18 should do the trick.

- Drilling out my pump jets to .62mm, I still need a slightly fatter shot when I get on it. By optimizing (leaning out, in my case) all the other circuits in the carburetor, the pump shot needs to do more work to keep the mixture proper now that everything isn't masked by running overly rich..

- Re-sync and re-tune idle

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Idle Mixture Screw Pitch on 40DCOE2 is 0.8mm

I'll measure it on the 40DCOE151's when I get close to them(100km away presently)

The other important part to measure is the taper of the screw. I'll measure that optically.

For the record the 40DCOE151's thread is also 0.8mm. I'll measure the taper.

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Oh, there she is. Thanks for the link.

So I'm new to the tuning of Weber carbs, actually just bought a set of triple 40 dcoe with Cannon manifold. I just happened to catch a episode of Wheeler Dealers where they tuned a carb'd Lambo with this at idle to match airflow:

Air Flow Meter Synchrometer - Dune Buggy Parts, Sandrail Parts, VW Parts - MooreParts.com

Has anyone used this unit or similar?

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I just want to thank you guys for posting all this great info.

Just finished the resto on my series 1 and after a shake out drive this weekend discovered the notorious flat spot at about 2200-2500rpm. I'd set the floats to 8.5mm but know the actual fuel level is about 32-34mm below the jet well surface.

Btw, my carbs are 40DCOE-18's.

This thread gives me hope that the fuel level is the main culprit. Now if I can just stay clear-headed while digesting all the data!

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Good stuff Chuck! Try the fuel height at ~ 27-29mm and report back if you can.

Also let us know what the jets, tubes, chokes, and motor details are. Data is king.

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Great thread here guys, thanks for the information.

I have a situation with mine that I'm hoping someone can shed some light on.

Dcoe 40's, stock cam l26 f55 idle jets, float level on all set correctly, synced perfectly, timing at 18degrees initial with a recurved dizzy.

Cruise afr is 12.5 to 13 but my idle needs to be very rich (9.5) or I get popping through the carbs when transitioning to cruise rpm.

Any ideas? Car runs great otherwise. Just a little baffled as to my my idle need to be so rich.

Thanks,

Dean

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A few more questions...Need more data...

Which F55 jet are you running?

55f8

55F9

55F11

Also, what Etube are you running and what air corrector and main jet

What do you consider cruise RPM.

So when your idle is at 9.5:1 your cruise rpm is pretty good. You could actually afford to lean it out a bit more in the cruise afr.

More info would be nice though before just guessing.

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A few more questions...Need more data...

Which F55 jet are you running?

55f8

55F9

55F11

Also, what Etube are you running and what air corrector and main jet

What do you consider cruise RPM.

So when your idle is at 9.5:1 your cruise rpm is pretty good. You could actually afford to lean it out a bit more in the cruise afr.

More info would be nice though before just guessing.

Idle55f9

170 air corrector

F11 emulsion

130 mains(way too rich,have ordered 120's

Cruise is around 2200 rpm

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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.

 

 

Tuning data:

post-6852-0-88044500-1439208039.jpg

 

 

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

post-6852-0-10072900-1439166760_thumb.jp

post-6852-0-88044500-1439208039_thumb.jp

Edited by Blue

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