What size venturi fuel and air jet do i need
07-02-22, 02:59 PM
#1
Poor boy rotary
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What size venturi fuel and air jet do i need
I'm going to do a Webber 48 IDA setup but I cant figure out what Venturi Choke, Air Jet, and Fuel Jet I need.
The options are:
Venturi: 36mm-46mm
Fuel jet: .085-.240
Air jet: .100-.230
The options are:
Venturi: 36mm-46mm
Fuel jet: .085-.240
Air jet: .100-.230
07-03-22, 10:04 AM
#3
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the venturi is the easy one, it either gets sized to the port, or the rules if you're racing. for example the 12A peripheral port has a 43mm intake runner, and runs a 43mm venturi... it gets harder with a 4 port, i know.
the idle jet will probably be in the 55-65 area, although it depends. the Emulsion tube goes with the engine, there is a chart, but F7 for a 12A and F8 for a 13B i think
the main jet depends on how much HP you're making and what mixture you want and the BSFC, so its hard to predict (fuel pressure and float level matter too). a 6 port 13B is going to need a bigger jet than say a P port, because the P port is more efficient
and the air corrector just needs to be tuned to the car, estimate is about 50 down from the main jet, but that is just a ballpark you need to try different ones
https://www.rx7club.com/1st-gen-gene...paper-1145099/
the idle jet will probably be in the 55-65 area, although it depends. the Emulsion tube goes with the engine, there is a chart, but F7 for a 12A and F8 for a 13B i think
the main jet depends on how much HP you're making and what mixture you want and the BSFC, so its hard to predict (fuel pressure and float level matter too). a 6 port 13B is going to need a bigger jet than say a P port, because the P port is more efficient
and the air corrector just needs to be tuned to the car, estimate is about 50 down from the main jet, but that is just a ballpark you need to try different ones
https://www.rx7club.com/1st-gen-gene...paper-1145099/
07-03-22, 05:37 PM
#4
As j9fd3s mention, float level matters so you should get that set first. Pierce Manifolds has a good tech article that covers this: https://www.piercemanifolds.com/category_s/316.htm Pierce sells a float setting tool that makes this easier - which I think their part number PM1515. They list it as an IDA 40 float tool so call them to confirm that it works for a 48IDA. Its one of those things you wont use allot (my weber maintains float level really well) but is niece to have when you need it.
To add to that, you want to make sure fuel pressure is around 3psi. And yes, the emulsion tube matters a great deal on these carbs so find out what you have and research their characteristics. Below are the Jets I am using on my GSL/SE 13B based street port racing engine. These jets were dyno'd with both 42mm and 44mm chokes. Intake and exhaust porting on my engine is not real extreme but it will have more overlap that the stock ports.
195 Main Jet
120 Air Corrector
F7 emulsion tube
60 Idle jets
I could go leaner on the Main Jets (or higher on the Air Corrector) per JPM but on track my Pyrometer is reading 1500-1550F @6" from the exhaust port so this is safe jetting for my car.
To add to that, you want to make sure fuel pressure is around 3psi. And yes, the emulsion tube matters a great deal on these carbs so find out what you have and research their characteristics. Below are the Jets I am using on my GSL/SE 13B based street port racing engine. These jets were dyno'd with both 42mm and 44mm chokes. Intake and exhaust porting on my engine is not real extreme but it will have more overlap that the stock ports.
195 Main Jet
120 Air Corrector
F7 emulsion tube
60 Idle jets
I could go leaner on the Main Jets (or higher on the Air Corrector) per JPM but on track my Pyrometer is reading 1500-1550F @6" from the exhaust port so this is safe jetting for my car.
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