Quote from JjyKs on May 3, 2022, 7:06 am

Got sick of my carbs being out of tune and not finding anybody with expertise to tune them without half a year of waiting here in Finland and finally bought the dual quad set. I have experience with EFI systems (megasquirt) from my earlier Porsche 924 Turbo, but this kind of dual throttlebody injection is new to me.

I've been trying to find how these are supposed to be plumbed, but no luck so far. I'm using external fuel pump and return line. Most of the installations use a sump tank and no return line from throttle bodies.

So here are the options I've figured out: Note there are 3 possible inlets, but only one outlet that's

In parallel
Possible cons: In theory all fuel might go through one of them, causing the other to vapor lock? Also a tiny difference between pressure regulators might cause another one to starve.

Inputs in parallel, second return blocked

This one was actually something I saw in a youtube video of a running a car so it should work. However somehow this seems like a bad idea to me. Might have problems filling the 2nd throttle body with fuel after sitting in a hot environment?

In series

Cons: No idea how 2 fuel pressure regulators work when connected like this. Does the 2nd TB get enough pressure?

In series, using input port of 1st TB as an unregulated output for 2nd one

Possible cons: Is the TB designed to flow like this between 2 inputs, or would it be possible to starve the 1st TB of fuel?

I've been trying to find how these are supposed to be plumbed, but no luck so far. I'm using external fuel pump and return line. Most of the installations use a sump tank and no return line from throttle bodies.

So here are the options I've figured out: Note there are 3 possible inlets, but only one outlet that's

In parallel
Possible cons: In theory all fuel might go through one of them, causing the other to vapor lock? Also a tiny difference between pressure regulators might cause another one to starve.

Inputs in parallel, second return blocked

This one was actually something I saw in a youtube video of a running a car so it should work. However somehow this seems like a bad idea to me. Might have problems filling the 2nd throttle body with fuel after sitting in a hot environment?

In series

Cons: No idea how 2 fuel pressure regulators work when connected like this. Does the 2nd TB get enough pressure?

In series, using input port of 1st TB as an unregulated output for 2nd one