Ive been trying to get this tuning dialed in on this 383 for months and it seems to be everchanging. The setup is a carb 383 with speed demon 750 carb running through an in-tank 255lph pump and an aeromotive return style regulator. The oddest thing will be this:

Problem 1:
Today i started the car and fuel pressure was about 6.5 psi which is exactly where i want it. The air/fuel is stoichiometric and the car is running great. I turn it off and start it again about 1 hr later. Fuel pressure is about 3.5 psi and both fuel bowls are completely full. Car is running very rich and begins to fowl plugs. In the between time nothing has changed. What can cause this? I can adjust the car to raise fuel pressure and lower floats and it will be fine for a while. The the psi will be too high and floats too low. I just cant seem to figure this out.

Problem 2:
Timing is dialed in and car idles and revs with no backfiring. Yet when i attempt to drive it it backfires very badly and runs very poorly. How could a load being placed on this motor change things?

Thanks guys

 

The motor also dieseled today when i shut it off. Seems to run great at all rpms when in neutral but when in gear it seems to spit and sputter.

 

I'm not sure what would cause the fuel pressure change unless the regulator or pump is bad or being used in the wrong application. I'm assuming the in-tank pump and regulator are designed to work together with the correct pressure ratings. I would take the regulator apart and make sure it looks ok, nothing broken or dirty check the easy obvious stuff first.
A lot of times a car will act completely different under load vs. idle. The backfiring sounds like it could be a timing issue. How big is the cam you are running? How much initial timing and total timing? Idle rpm?

 

The timing is 8 deg advanced at idle, roughly 900 rpm. The cam is a comp cams xe274h. Its 274/286 and about 236/240 @ .050. Lift is about .5-.51. I thought about dropping the initial timing down to about 4-6 deg advanced. It just seems like its running lean when its in gear. I have an air/fuel guage and it reads stoichiometric when idleing. Im probably going to invest in a wideband air/fuel meter in the near future.

 

With that cam I would try more timing, atleast 16-18 degrees at idle and 34-36 total. It should idle much better and more consistantly with more timing.
You may have to do a little carb tuning too but that cam is mild enough you shouldn't have to tune it a whole lot. Be sure to pay attention to the transferslot positions on the carb when tuning, its easy to get way rich or way lean if you get too far out of adjustment. Only a small amount of the transfer slot should be exposed. Demon carbs are notorious for being rich, some people love them and others have nothing but trouble. I'm not too familiar with the demon Idle eze setup its a little different than tuning a normal holley but I found a couple of posts about tuning demons that may help you out.
https://www.thirdgen.org/forums/carb...=transfer+slot

https://www.thirdgen.org/forums/carb...=transfer+slot


Hopefully that helps a little, you may have already done that stuff but if you haven't give it a try.