Swap fuel plates to help lean out bottom end response?

Is that a jab or what? If I've missed the data then I've missed it; to be honest I dont know at what point in the rpm/boost/throttle position relationship where the plate is/isn't involved and at what point does the off-idle response get affected - hence the point of this thread.
 
No jab intended. Weston doesn't always post all the answers, but his hints are often trail markers to the correct path. It was a bit more confusing before i made a fixture so i could see what was happening. Have you taken the afc off and played with the throttle while it's running to see where the arm isin relation to your throttle position?
 
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^understood; I like to clarify.


And no, havent run truck with afc off...figured oil would be slinging out everywhere, HA. But I will, as I am going to have some time available soon. Let's carry on!
 
The name of the two parts should divulge their purpose.

Fuel stop plate(rack stop) and aneroid fuel control(air to fuel control).
 
Hurley said:
^understood; I like to clarify.


And no, havent run truck with afc off...figured oil would be slinging out everywhere, HA. But I will, as I am going to have some time available soon. Let's carry on!
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It may sling a bit of oil, but not bad. It will clarify though.:poke:
 
^ISWYDT


It appears to me that the ability of the AFC to control off-idle and lower end fueling/response isnt as precise as its ability on the upper end of its operation range? And by that I am thinking about spring rate versus AFC arm position at the lower end of measured movement..... or is that completely wrong?
 
Hurley said:
^ISWYDT


It appears to me that the ability of the AFC to control off-idle and lower end fueling/response isnt as precise as its ability on the upper end of its operation range? And by that I am thinking about spring rate versus AFC arm position at the lower end of measured movement..... or is that completely wrong?
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Looks like it's confirmed.

To some degree yes. The governor arm is not in contact with the AFC foot at idle and takes some amount of rack travel before it does make contact. With larger injector orifices and modified DVs, that unrestrained distance can be enough rack to deliver too much fuel too quickly.

Diaphram Screw: start location of AFC foot
Starwheel: preload to determine at what psi AFC foot starts to move
Spring: how much AFC foot advances per psi of boost
Plate: Limits max rack travel (duration)
 
Have you ever gotten the afc arm back so far that when you put it in drive and step on the pedal nothing happens. Then when you start turning the pre-boost screw a little bit at a time it starts working.
 
RonA said:
Have you ever gotten the afc arm back so far that when you put it in drive and step on the pedal nothing happens. Then when you start turning the pre-boost screw a little bit at a time it starts working.
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yes, but instead of adjusting the pre-boost screw I slid the entire housing forward... that was also in conjunction with waaay too much spring preload (hadnt actually benched the afc at that point), and was 'back in the day' before I actually understood the purpose of benching the afc housing.


Straight-6: I understand the function of each component; I've just been asking if the plate profile ever became a limiting factor on the lower end -and based off of Ron's response I would see that if I had a pump 'jig'.


I guess the whole statement I am trying to make is that, in my mind, if I get a spring with the appropriate rate/free length/coil count to deliver full fuel a few psi before full boost (which appears to be what I want) all the while giving maximum foot travel, then the spring itself is going to be a little 'soggy' for my liking off of the bottom.
 
RonA said:
Have you ever gotten the afc arm back so far that when you put it in drive and step on the pedal nothing happens. Then when you start turning the pre-boost screw a little bit at a time it starts working.
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Exactly what I do, when you cut the bottom end fuel so much that you can drive off from a stop light like a normal truck with your foot on the floor, you are now in control of the bottom end fuel, I usually go in 1/2 turn increments on the pre-boost fuel screw from there.

Jim
 
I knew it would make sense to you Jim. I'll have to show you the piece I made to take the place of the diaphram and cover. It always seemed like they went out of their way to make it hard to get full travel with a heavy spring and not coil bind. The afc needs to sit all the way to the rear but still allow full rack travel. never saw the point of the slotted cover unless you are running everything stock.
 
^^(Ron) That's an insightful post. Sounds like I just need to find the right spring to begin with....

instead of trying to 'make this one work'? (I'm still going to fiddle with the plates some)
 
Jim Fulmer said:
Exactly what I do, when you cut the bottom end fuel so much that you can drive off from a stop light like a normal truck with your foot on the floor, you are now in control of the bottom end fuel, I usually go in 1/2 turn increments on the pre-boost fuel screw from there.

Jim
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RonA said:
I knew it would make sense to you Jim. I'll have to show you the piece I made to take the place of the diaphram and cover. It always seemed like they went out of their way to make it hard to get full travel with a heavy spring and not coil bind. The afc needs to sit all the way to the rear but still allow full rack travel. never saw the point of the slotted cover unless you are running everything stock.
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Are you cutting the fuel this much with just the afc or a combination of governor springs, injectors and delivery valves? I've backed my pre boost all the way out, stretched the spring and slid it to the rear, but I definitely couldn't floor it from a stop and it not go anywhere.
 
^it's all in the spring selection/preload from the afc. I too have done that, no smoke, no-go, nada. But like i said earlier, I slid the housing all the way forward (was all the way back.)
 
I think there really could be a market for a company to make aftermarket springs for these afc's that are for the higher hp guys. I know tst has some but it seems like most guys need more spring.
 
Hurley said:
^it's all in the spring selection/preload from the afc. I too have done that, no smoke, no-go, nada. But like i said earlier, I slid the housing all the way forward (was all the way back.)
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I want to bench it again to see if the spring has softened at all. Might get some time tomorrow to mess with it.
 
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