Calling all triple carb experts

[NismoZ]

Ok I recently bought a set of Dellorto 40 carbs for my 240z.. Then engine is a stock L28E long block with headers and exhaust. I need to know what should be the correct jetting for these, Im trying to find out what the ballpark figures should be before i bolt them up and have drivabilty issues..

I know its not really possible to say what exact sizes should be used do to sea level, location and the weather but i think any experienced tuner could give ball park figures to work with.

With all that said the carbs are Tuned with 32 chokes, 57 idle jets, 132 main jet, 180 air correction jet, 38 pump jet and #11 emulsion tube and 5 progression holes.. How does this setup sound?

I am Located in the Sunny So Cal in LA

Thanks

[Babalouie]

There's a great thread on HybridZ on triple carb setups, I'm sure what you are looking for will be in there somewhere: http://forums.hybridz.org/showthread.php?t=93343

But FWIW, your setup does sound in the right ballpark.

Mine are Weber 40s (so I'm not sure how comparable they are to Dells) but mine are 32mm choke, 50 idle jets, 125 main, 175 corrector, #11 'tube. Checked out on the dyno just fine. Motor is a mild L28. If the Dells are the same, then I'd say you're starting point would be close to the money.

[Bcalvosa]

If you don't already have it, grab a copy of HPBooks "How to Modify Your Nissan/Datsun OHC Engine" -- very helpful book. The below formulas are gleaned from there. A narrow band oxygen sensor in the exhaust can help you tune idle and cruise jetting, a wide band can help with power settings. Dyno time is extremely helpful, albeit expensive.

40mm carbs are small for best high RPM performance on an L28, but are streetable. 44 or 45mm carbs would be better.

• Main Venturi size should be around 36mm.
  
• An initial main jet choice would be .04 times the main venturi size (or 1.45 in this example)
  
• An initial main air correction jet should be .2 larger than the main jet (1.65 in this example).
  

Search the forums for jetting recommendations for Mikuni, Weber, Solex, or Dell'Orto (they all work off of the same principles).

For reference, my jetting is:

2.4L w/ triple 44mm Mikuni's, header, headwork, etc.

• 34mm Main Venturi
  
• 1.50mm main jet (note that the initial recommendation formula gives 1.36)
  
• 1.80mm air correction jet (still tuning this - I may need to go a little larger to maintain high RPM mixture).
  
• .65mm pilot jet
  
• .45mm pump jet
  
• 1.6mm starter jet (rarely use the "choke" system, so not that important)
  
• Idle air ports enlarged from 1.2mm to 1.3mm to give better mixture under light cruise acceleration.

Some examples of jetting I've noted from other posts:

A Nissan Tech with an L28 was using:

• 37mm Venturi
  
• 160 Main
  
• 180 Air
  
• 55 Pilot
  

Mikuni default jetting for the 44mm carbs (seem set up for an L24):

• 34 Venturi
  
• 150 Main
  
• 200 Air
  
• 57.5 Pilot
  
• 40 Pump
  

Nissan Motorsports 16010-E4620 carbs came set up for an L28;

• 37 Venturi
  
• 175 Main
  
• 250 Air
  
• 55 Pilot
  

I believe Jon Mortensen noted he was once running an L28 with:

• 37 Venturi
  
• 155 Main
  
• 210 Air
  
• 67.5 or 65 Pilot
  
• 50 or 45 Pump
  

Good luck to you

[NismoZ]

Thanks Guys... really appreciate the help. I do happen to have the "How to Modify Your Nissan/Datsun OHC Engine" book and I just orderd the How to power tune Weber & Dellorto carbs... Im glad to hear i should be in the ball park.

[Babalouie]

Thanks Guys... really appreciate the help. I do happen to have the "How to Modify Your Nissan/Datsun OHC Engine" book and I just orderd the How to power tune Weber & Dellorto carbs... Im glad to hear i should be in the ball park.

I did the same thing as you...worked out the jetting based on the books and Weber rules of thumb. And when I put the car on the dyno to check the tune, the guy said "don't change a thing...it's fine the way it is" Old school rules of thumb appear to still work in a digital age

[Lazeum]

I've learned how to tune my carbs with a wideband (Innovate LM2).

Kind of expensive but I've learned a lot in the process and I had a good time doing it + I know some basics about tuning now

On the other hand a good wideband is not more expensive than a dyno session with a tuner.

I found the process to be very rewarding when I was doing a good change (90% of the time). Car screams and feels strong!

FYI, I had a L28 high comp / mild cam (I had since combo was not so great because of low timing to fight knock):

40's Weber with 32mm venturi, 45f9 idle jets, 135 main, 180 air, F11 emulsion tube & 45 Accel. Air jets should be a step higher (195)

Edited January 20, 2010 by Lazeum

[NismoZ]

Any of you guys know if the fuel banjos from weber fit the dellortos?

Im looking for banjos Like this

http://cgi.ebay.com/Dellorto-DHLA-Carburettor-fuel-banjo-double-hi-flow_W0QQitemZ290375966338QQcmdZViewItemQQptZUK_CarsParts_Vehicles_CarParts_SM?hash=item439bc19e82

My carbs are currantly equipped with three banjos like this

http://cgi.ebay.com/Dellorto-DHLA-Carburettor-fuel-banjo-Single-hi-flow_W0QQitemZ290377204277QQcmdZViewItemQQptZUK_CarsParts_Vehicles_CarParts_SM?hash=item439bd48235

Hopefully i could find some here in the states that are not overpriced

Edited January 22, 2010 by NismoZ

[NismoZ]

Any of you guys know if the fuel banjos from weber fit the dellortos?

Im looking for banjos Like this

http://cgi.ebay.com/Dellorto-DHLA-Carburettor-fuel-banjo-double-hi-flow_W0QQitemZ290375966338QQcmdZViewItemQQptZUK_CarsParts_Vehicles_CarParts_SM?hash=item439bc19e82

My carbs are currantly equipped with three banjos like this

http://cgi.ebay.com/Dellorto-DHLA-Carburettor-fuel-banjo-Single-hi-flow_W0QQitemZ290377204277QQcmdZViewItemQQptZUK_CarsParts_Vehicles_CarParts_SM?hash=item439bd48235

Hopefully i could find some here in the states that are not overpriced

Ill Take that as a no i guess... anyways im still waiting on the book i ordered so i will need to ask some questions on the floats..

How do you set them on the Dellortos? I was told 15mm gap between lid gasket and top of float 23mm float drop.. sound right to you?

And if they need to be adjusted how do i go about doing so? I know im suppose to bend it somewhere but where..and how?

[Nigel1943]

Ill Take that as a no i guess... anyways im still waiting on the book i ordered so i will need to ask some questions on the floats..

How do you set them on the Dellortos? I was told 15mm gap between lid gasket and top of float 23mm float drop.. sound right to you?

And if they need to be adjusted how do i go about doing so? I know im suppose to bend it somewhere but where..and how?

There are 3 float weights available, 7.0 grams, 8.5 & 10.0. These weights should be marked on the bottom of the float.

Distance settings should be carried out by holding the carb cover vertically with the gasket installed so that the measurement between the gasket and the float should be:- 10gram, 16.5-17.0mm, 8.5gram, 15.5-16.00 and 7gram, 14.5-15.00mm. Tweak the metal "ears" to achieve this. The "ear" should be just resting against the needle valve during this operation.

[NismoZ]

There are 3 float weights available, 7.0 grams, 8.5 & 10.0. These weights should be marked on the bottom of the float.

Distance settings should be carried out by holding the carb cover vertically with the gasket installed so that the measurement between the gasket and the float should be:- 10gram, 16.5-17.0mm, 8.5gram, 15.5-16.00 and 7gram, 14.5-15.00mm. Tweak the metal "ears" to achieve this. The "ear" should be just resting against the needle valve during this operation.

Thanks Nigel, now what about the float drop? does it really matter?

[Nigel1943]

Thanks Nigel, now what about the float drop? does it really matter?

25mm.

[NismoZ]

There are 3 float weights available, 7.0 grams, 8.5 & 10.0. These weights should be marked on the bottom of the float.

Distance settings should be carried out by holding the carb cover vertically with the gasket installed so that the measurement between the gasket and the float should be:- 10gram, 16.5-17.0mm, 8.5gram, 15.5-16.00 and 7gram, 14.5-15.00mm. Tweak the metal "ears" to achieve this. The "ear" should be just resting against the needle valve during this operation.

Thanks for the help Nigel, Just to clairifiy what exactly do you mean by The "ear" should be just resting against the needle valve during this operation? Does that mean right as it touches the round head but no compressing the spring??

Edited February 8, 2010 by NismoZ