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RX7 13B 6 Port blow through carby problems

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Old 07-09-17, 08:03 PM
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Question RX7 13B 6 Port blow through carby problems

The engine starts instantly with an Hitachi 18S turbo & a 48 DCO SP2 Weber carby set up.
After warm up, the engine runs to 3000 RPM for as long as you want it to,then if I attemp to increase RPM,the engine splutters,If I give it WOT, it dies like the ignition is turned off.
It has an 8 PSI waste gate spring, A Aeromotive fuel regulator with return to fuel tank with a fuel pressure gauge set at 3 PSI. Ignition timing is set to timing marks with vaccum advance.
The carby has 2, 40mm Venturis, Fuel jet 195,Air Jet 205, E-tube F4 & 300 needle Valve.
The engine has an indent porting.
I'm assuming the engine runs up to 3000 RPM on Idle jets then changes to main jets after 3000 RPM. Any ideas to sort out this problem would be appreciated.
May be I might need another electric fuel pump with higher PSI. It has the same electric fuel pump when it was naturally asperated,do not know what PSI it is.
The engine ran excellent with the same carby jets,venturi's,etc when it was naturally asperated.
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Old 07-10-17, 01:00 PM
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I do not have experience with carbs on rotaries but I would venture to say that the car is dying when you start to build boost because having positive pressure in the carb could be screwing up the venturi effect needed to pull fuel in the first place. In a fuel injected car you need to run a rising rate fuel pressure regulator that raises the fuel pressure, usually at a 1:1 ratio compared to boost, to make sure you have more pressure behind the fuel than in the intake so the fuel will actually enter the intake.

Hopefully others can chime in but that would be my thoughts on what is causing your problems. So at the least I would think you will need a better fuel pump and a fuel pressure regulator that connects a vacuum line to your intake so it can tell when you are boosting to know when and how much to raise the fuel pressure.

Now whether or not your jets are even remotely sized well enough to not blow up your engine with boost is an entirely different story and I would be very careful if I were you.

Last edited by Lavitzlegend; 07-10-17 at 01:02 PM.
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Old 07-10-17, 08:25 PM
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Thank you Lavitzlegend for your input,I do have a regulator that connects to the vaccum intake but not connected, I'll connect it & put a Holley Blue electric fuel pump on & see if that sorts it, cheers
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Old 07-13-17, 07:38 AM
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u need a fuel injection pump connected to a rising rate regulator , the holley blue pump wont be enough psi for a blowthru set up , and connect the regulator to a boost only source u dont need vacum on a carb set up
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Old 07-13-17, 10:58 AM
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What Lavitzlegend and wicked said is wrong based on a common misconception which needs to end. You do not want to use a rising rate fpr. Ever. What you do need is a boost referenced fpr with a 1:1 ratio like the Mallory 4309.

As for the rest of your setup, the weber is crap for boost and I can't hep you with it. I don't know what indent porting is but it doesn't sound pleasant. Oh and why do you have vacuum advance still hooked up?
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Old 07-13-17, 07:40 PM
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Boost reference , rising rate Regulator is the same thing , the main thing that u need is a fuel injection pump with a regulator that can be adjusted to the psi your carb was meant to run wich is like 3-5 psi. , and the regulator has to be boost dependent meaning it will raise the fuel psi 1:1 to the boost is seeing , u will need to run a return line for this set up
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Old 07-16-17, 08:25 PM
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Thanks Jeff 20B,What sort of carby would you prefer than a weber for blow through ? It's an extend 6 port. I've disconnected the vaccum advance now. I need a carby that will adapt to a horizontal intake manifold made by Atkins aviation ,inother words, a side draft carby. Would you know of a good sidedraft?
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Old 07-17-17, 10:23 AM
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Originally Posted by Jeff20B View Post
What Lavitzlegend and wicked said is wrong based on a common misconception which needs to end. You do not want to use a rising rate fpr. Ever. What you do need is a boost referenced fpr with a 1:1 ratio like the Mallory 4309.

As for the rest of your setup, the weber is crap for boost and I can't hep you with it. I don't know what indent porting is but it doesn't sound pleasant. Oh and why do you have vacuum advance still hooked up?
What do you think is happening with a boost referenced fuel regulator? The fuel pressure is RISING at a RATE of 1:1 with the boost pressure... They are the same thing...

As to the comments about whether the carb is well suited for a boost setup I have no clue. I was just trying to point OP in a proper direction to start trouble shooting problems since no one else had replied at that point.

Why not just go fuel injected so you have easier ways to data log what is happening and directly adjust the values based on the data? There are some good Weber replacement throttle body setups with injectors from Borla Induction and TWM. The only downside is it will likely cost more to get all the parts initially. Just my personal preference
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