Negative Fummins.

The "smoke screw" is just a base preset. What that does is set the "0" resting position of the rack. The further in you screw it, is your base minimum level of fuel at any point. So if you have a setup that flows very high CFM at/off idle, you would increase this. Aftermarket turbos on OEM 160hp injectors, would increase this.... Larger injectors, would keep this backed out, and then use the star wheel to incorporate when flow is increased.


So really, the start screw is what your idle air screw would be.... ;]

 

Sorry Fox, but I disagree. The smoke screw sets the idle/zero position of THE AFC FOOT, NOT the rack....the rack can in fact back off boyond the resting point of the AFC foot. Hence, when you push the throttle, advance the rack, the smoke screw lets you advance it until it hits the foot when it would then be controlled by boost pressure. Also, CFM and Pressure are NOT the same thing.... but this is no place for arguing, and who cares about carburators on this site anyway???

 

Correct... your right, I used the wrong term when I said rack.... But overall my statement was correct. The smoke screw on the back of the AFC, does only adjust base fuelling point.

And yes, I know CFM is different than pressure. Hence why I used CFM. LoL.


I've done my share of engine porting and building Fummins.

 

So I took it off again today, I still have to use air to set the star wheel but once I got that access plate to the diaphram off again and started playing with it I saw how it was bottoming out and limiting the travel of the foot. So I flipped the one washer and put it on top of the spring and them used a washer I had on top of the diaphram now it allows full travel of the foot with the 1/8 inch I took off the end of it. The "smoke" screw, I loosened the jam nut and then with the access plate back on the diaphram I turned the allen screw in until I made contact with the shaft and moved the foot and then gave it a half turn and snugged the jam nut. I was playing with it for about an hour or so trying to understand how it all works and I think I have a basic understanding now...I think...I'm sure someone will let me know if I don't. I'm getting the 2095 rack plug from a local shop too.

 

Sounds like you're well on your way!

The AFC is an Aneroid Fuel Control....."Aneroid" meaning "by air", so Air Fuel Control, if you'd like. See the picture below. The little arm thingy in the middle is the throttle arm; it is attached to the throttle shaft and the rack shaft. It has a little foot on the top end that advances forward moving the rack (thus turning the barrels and giving more fuel). It comes in contact with the AFC foot and eventually the fuel plate, riding along the fuel plate profile as RPM's increase, thus the plate profile dictates WOT rack movement and can increase or taper off the fueling based on the peaks and troughs of the plate profile. The AFC (Air Fuel Control) foot stands in the way of the throttle foot and the "full fuel" plate during no- or low-boost conditions to prevent overfuling. As boost is built, the air pressure pushes the diaphram which advances the foot and allows more fuel to be added as per the presence of boosted air signal, ideally at the rate of just a mild haze of smoke if tuned properly. The "smoke screw" simply advances the AFC foot forward without air pressure influence and gives you that extra bit of no-boost fuel for takeoff, generally causing a bit of fuel dumping and thus smoke hence why it's called the smoke screw.



I have my smoke screw backed all the way off, but the AFC housing slid full forward, which also acts the same as bumping the smoke screw a bit because it's advancing the AFC foot in front of the throttle foot. I then tuned my AFC for mid stroke at 15psi and full stroke at 35 psi with shop air...I did this by attaching a blow gun with pressure regulator and dialing the pressure to 15 and 35, blowing in the diaphram port and adjusting the star wheel so the spring rate would produce the results I wanted. I have hardly any smoke and fairly smooth acceleration. I'm also running an "industrial" fuel plate full forward, which I believe is closest to a #12, for what that's worth.

Hope this helps!

 

Thank you for all the information on the AFC, between what you guys have said and having it my hand and actuating it I think I have a grasp on it. But before I properly tune the AFC I have to fix the problem. I have ZERO smoke no matter what I do. There should be some no matter what but there is absolutely none. Something is clogged or broke, pressure or volume. I'm going to pick up a fuel filter tomorrow. I also stopped at a local diesel shop and they said there is a banjo bolt with a ball valve on the pump near the head, there is a spring in there that controls pressure, the old girl is in the garage right now so I think I'll go check that out. Any other suggestions?

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UPDATE: I got that bolt out, spring was intact and had 3 shims I'm not sure if its the proper tension though so I will take it to that shop tomorrow.

 

I believe that "banjo bolt" you are referring to is the Overflow Valve - OFV. Search it on here to find the pen spring mod you can do to increase the fuel pressure fed to the injection pump. Those OFV's wear out over time and get weak and can really hinder the pressure supplied to the pump thus reducing power by simply evacuating too much fuel through the return line. Tork Tek also makes replacement OFV's that have reduced orifices to keep pressure up.

 

I put a pen spring in the OFV and made sure that the ball was in there, did fuel filter too. Still no smoke. Going to try and run it off a fuel can tomorrow and borrow my buddies pressure tester. I gotta figure this out, Its driving me nuts!

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UPDATE: I pulled the return line and fired it up and fuel came out. Then I ran it off a gas can, same thing. It does start hard when its cold and sometimes dies, and idles around 500rpm I think. I am pretty sure its my pump...

 

i seriously seriously doubt its your IP pump it could be low fuel pressure from your lift pump? are the mods in your signature all you have done to the truck? if so you havent added much fuel and it ISNT gonna smoke much. things dont start smoking much till DV's, injectors, gov springs and big laggy turbos.

 

I was thinking timing? Rack hung up not allowing travel? Idle seems low. I don't know, I've been at this for 3 days and I'm stumped. Good thing the girlfriend likes the smell of diesel.