Question for the slow ole guy, or other carb guru folks

[andyb]

Just because I don't actually know:

If you use the choke, I'm thinking you need a fairly strong vacuum differential to make it actually throw more fuel into the thing.  It's an enrichment and not properly a choke, but that's neither here nor there.

Does it add fuel at WOT/high-rpm also?  You'd have a bunch less vacuum differential between things, though you'd have a boatload more venturi effect (which shoves the slides around and increases flow through the main/needle jet area, obv).

Was just sitting trying to figure out something and I simply couldn't wrap my head around how the flow works.  Anyone?

[SlowOldGuy]

Andy,
Not sure exactly what your question is.  In the FJ carbs, the choke is like a separate sub-carb.  It has it's own fuel/air circuit.  Fuel is drawn up from the float bowl where it initially mixes with bleed air from the 4 small hoses attached near the top of the bowl.  This rich mixture is pulled by direct intake vacuum present at the choke outlet port which is located on the cylinder side of the throttle plate.  The air supply for the circuit flows from the air box and underneath the slide diaphragm to the choke outlet port

Being on this side of the throttle plate, the choke circuit sees a high vacuum signal.  This is also why it's a bad idea to give it any throttle when cranking with the choke on.  Adding throttle reduces the vacuum signal seen by the choke circuit and just dumps more lean air into the mixture, defeating the choke operation.

The total amount of choke mixture is controlled by the needle on the choke plunger which is why adjusting the choke also changes the engine speed (the choke plunger is acting like a throttle plate for the circuit).

When the choke is off, the plunger seats and stops any flow from the circuit during normal (or WOT) operation.

Is that anywhere close to answering your question?

DavidR.

[andyb]

Specifically, at WOT.  At idle, more fuel is dumped into the motor as the plunger is pulled.  But with the gas on hard and the revs up high, is it continuing to feed additional fuel through the enrichment circuit?  

If I do a WOT plug chop with the choke on, will I get a hilariously rich read?  It's something I've never done, I was curious.

Sounds like the answer is no, as the relative lack of vacuum would prevent the choke from effectively funneling more fuel out.