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Jetting Twin Dellorto's DRLA in A15
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Hi all!

I'm in the process of building up an A15. It'll feature some modifications as: Ported Intakes (2.25mm), lowered head (0.6mm), lightened Flywheel (5.8kg), Fast Road Camshaft and 2 Dellorto DRLA 40's!

I'm in the process of jetting the carbs, but theorically, it all just seems soo confusing...

From this tutorial: http://www.nzdatsun.com/forums/viewtopic.php?f=17&t=342

I got this setup:
Dellorto DRLA 40's
Venturi: 33mm
Main Jet: 132
Air Corrector: 180
Emulsion Tube: 7772.6
Iddle Jet: 40 / 7850.1

But then started reading more, and checked some other jetting engines, and It all just seems confusing.

Can some jetting expert guide me through a "safe" starting point to jet my engine?

Posted on: 2/17 1:08
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Re: Jetting Twin Dellorto's DRLA in A15
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The most important thing is: Venturi Size. All the other setting depend on it. Jetting for 32mm venturis differs from jetting for 28mm venturis

Posted on: 2/17 2:07
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Re: Jetting Twin Dellorto's DRLA in A15
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Well, I used the chart above to calculate that I might need a 33mm venturi, but what about the other jets? Thats the difficult part

Posted on: 2/17 22:08
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Re: Jetting Twin Dellorto's DRLA in A15
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That's the easy part. For ballpark correct A/F ratio:
* main jet is 4x venturi size = 132
* air jet is main jet + 50 = 182

Now for the hard part: transitions ... when the throttle changes, how much fuel it requires it differs with different engines and camshafts. These seem like a good starting point:
* Emulsion Tube: 7772.6
* Idle Jet: 40; air bleed: 7850.1

To be "safe" means make sure the A/F ratio never goes lean (lean = above 14.7:1). That means starting rich, later when you tune the carburetor you'll lean it down to best performance. Best full-throttle power: 12.5:1 ratio. Best cruise: 14:1. Best economy @ level cruise: around 15:1

Posted on: 2/17 22:25
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Re: Jetting Twin Dellorto's DRLA in A15
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Well, that's basically what I concluded from above.

So, is that a safe starting point for my tuning?

Posted on: 2/17 23:16
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Re: Jetting Twin Dellorto's DRLA in A15
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Yes. Be careful while you are tuning, don't let the engine ping/rattle

Posted on: 2/17 23:18
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