Ignition or carb problem? 440

[oldcarnut]

Sorry this may seem long, but I want to put it all out there to save questions. I put a new 800 cfm Edelbrock AVS2 to put on my 440.  Tuned it in and it ran great for awhile. The cam in engine is unknown to me, but is a little more lumpy than stock and draws around 10"-11" vacuum but still could get the idle adjustment ok.  After running on the car with some road trips and around town, things started turning for the worse getting it to cold start up and idle. Sometimes getting it to fire up would sound like it was either missing on a few cylinders, flooding out, choked off, or bad timing until it cleared enough to feather throttle up rpms. Occasionally it would blow back a mixture of gas mist and droplets out the top of carb. when it failed to start up but stumbled until it died. Once I got it to fire off and get warm enough to idle and not shut off, it seemed fine. I could throttle up it fine once I passed that stumbling. No hesitation and good acceleration. Idle was initially rough but got better the hotter the engine got, but when hot, idle rpm ran higher. Last trip home at cruising steady throttle, even at 3000rpm, it would start this surging type stumble same as the idle.  Then  it started some backfires at deceleration  Mash the throttle some, it would accelerate great and smooth. Let off and maintain any speed, back to a lumpy cam type surge. Things I have done to try and solve but no correction: Readjusted idle mixture screws, removed carb. top to recheck float levels and check for trash, blew air through jets and passages to clear out any trash-none found. Checked for vacuum leaks.  I have ran about 2 1/2 tanks of gas through it with no resolve for carb. misfire type stumbling to make sure it wasn't bad fuel. Tank and sending unit is fairly new.  Fuel filter was replaced and fuel regulator shows 5psi initial and down to 3 1/2 after getting hot. Tried a couple different step up springs and pump lever rod location. At this point I don't know what else to do with the carb.. Only improvement was moving dist. adv. to manifold vacuum side instead of ported which helped with staying at idling. Initial Adv is about at 15deg.

So this got me to look at ignition system.  Distributor/coil is a fairly new Firecore system, bought years ago, but very low usage while car was being restored. Rechecked timing, changed plugs, changed out plug wires, looked and cleaned cap/rotor electrodes. Nothing helped.  Is there anything else to check there? Can the distributor or coil somehow be contributing causing bad firing or vacuum advance issues?  I don't have another distributor to try a change out and don't want to spend more money trying for a fix. All was running good until it started not to.  Any advice? Next will be to swap carbs if I cant resolve it another way.

[Dino]

This sounds like an ignition problem. I had a Firecore ready to run system years ago. It worked good for a while but then problems started. I was sent a new coil and later a new distributor. Everything worked fine again but I sold it when I moved to EFI. Get a basic distributor and coil, and it will probably run just fine.

[b5blue]

My Firecore crapped out, when I called them they were shocked it lasted so long. MSD now.

[metallicareload99]

Manual or electric choke? How did the spark plugs that were in there looking?

[oldcarnut]

Electric Choke   I tried setting it further back open but no change.
Plugs looked good to me.  Both sets were about the same.

[metallicareload99]

Do you know how much vacuum advance you are getting and when it starts coming in? Might be worth checking how it runs with it disconnected? Be sure to plug the port on the carb

Just out of curiosity, what's the total timing @?

[b5blue]

I also put a manual choke on my Proform 750. 

[oldcarnut]

Do you know how much vacuum advance you are getting and when it starts coming in? Might be worth checking how it runs with it disconnected? Be sure to plug the port on the carb

Just out of curiosity, what's the total timing @?

Total is about 36 all in. Initial on manifold is around 15+.  Hard to keep it steady to check now under idle rpm without it starting to stumble and die. Originally it ran good at ported vac but when it started acting up I switched to manifold which improved some idlebilty and smoothness.  When cold now it runs bad at idle, worse on ported . Untill it gets up about 175deg I have to keep foot on the gas some when stopped in gear.  I found my old msd 6a system out of the garage I'm going to install and see if it makes difference.