I have searched as many previous threads as I could before posting this.
400 cubic inch rebuilt (professionally) 20k since rebuild. I have never been able to take the slight "mis" or a shudder out of this motor.

I Have just :

tested the Ign. mod.,
replaced wires,
set timing,
replaced dist. cap,
(again) checked all pulleys,
belts.
It is worse in the morning I have noticed. I have checked for vacuum leaks around carb, intake.
Have rebuilt the carb 2-3 times .
The previous motor locked up on me at 70MPH, cracking the Edelbrock cam in half. I used the Heads(they were magnafluxed, reworked), same Harmonic balancer, same flywheel etc. on this "short block" motor I purchased. Everything else is new.
WHAT GIVES?? I am so out of Ideas, all the simple stuff is pretty much ruled out.
PLEASE HELP!!

 

I bet you didn't test or check the vacuum advance on the distributor ?

Everyone forgets about this device.

How about the age of the distributor ?

 

The dist is about 3-4 years old., we checked timing, btdc, total advance etc. with a pricy snap-on timing gun. Im real close to pulling the heads and replacing, replacing intake gasket (someone said could be vaccum leak under the "turkey pan")
replacing harmonic balancer. I will give blood if I have to LOL

 

To check for vacuum leaks get a can of carb cleaner and spray it around where the gaskets are supposed to seal.

When the engine speeds up from idle ,that's your leak.

 

I stated earlier in this thread that I had changed the spark plug wires. But I havent in 3 years!!!!!!I have done the vaccum check with carb cleaner. I just got back from town. I decided I would change spark plug wires. The ones I had were Crane Hi-Performance wires. So, I havent bothered changing them in 3 years. I bought some AutoZone cheapies for $15, and it helped tremendously!!!
Each one of the old plug wires I tried to remove from spark plugs pulled from the metal retaining stem with no effort. After closer inspection, I noticed that inside the boots the conductors were very shriveled or burned looking. I think heat has done a number on these HI-Performance wires.
**BUT** There is still a noticable shake to the truck, but it sounds smooth You think I may need to replace the Balancer?
Thanks for the tips!! Please reply!!!

 

I have this same exact problem with my 400, the motor was also professionally rebuilt, the block was decked and line honed and the reciprocating assembly was balanced. I've done all the same stuff you have, replaced spark plugs, distributor cap, rotor, and spark plug wires. The distributor and vacum advance was replaced. Timing was set. I even put in a Pertronix ignition in case the points were the problem. I checked for vacum leaks last month. All of this and no change in the missing. Very frustrating.

The one cause I can pin down was that my intake gaskets started leaking about a year ago, which was four months after the motor was redone so it's now 18 months later. I had the gaskets replaced. That fixed it and the missing went away for about two months before it started doing it again- I even retourqued the intake to specs when it started missing. The missing gets worse when the engine has been running awhile. I've had to set my carburetor 6% rich just to make it as smooth as I can.

I have read that Edelbrock performers can leak _under_ the intake manifold, especially if the heads were milled, so I'm replacing the intake with a stock Ford 2 barrel at the earliest opportunity. I'm going to try cleaning the upper end with some sort of cleaning fluid like carb cleaner before I yank the intake.

The idle doesn't settle down either, it varies with the engine and ambient temperature and even with my diagnostic tach it rocks back and forth 20 rpm or so. I'm going to hate losing my 4 barrel carb, but I need to set this problem right. I'm trying to track down a 2 barrel autolite with the 1.33 size venturi, it's rated at 425 cfm - which is way better than the 351 cfm of the typical 2 barrel with the 1.21 venturi. At least it'll still have some power...

 

Yep, I have the edelbrock performer too, and a carter 625cfm 4bbl. I was considering a stock intake again myself. When I bought this truck, it was all stock, I put a carb kit in the 2bbl Motorcraft2150, and I could BOIL the tires with it, it idled smooth, ran cool,and everything.
Im with ya on that idea, soon as pocket permits,im hunting the junkyards for a stock intake and a motorcraft 2150 carb (just for the core). I think a core charge on the 2150 was about $75, you can get a rusted one from junkyard for $5-$10.
You mentioned that especially when heads are milled, the performer leaks. well, I had the heads milled .025"
Im now convinced anyone wanna buy an edelbrock performer intake and a carter 625cfm 4bbl??

 

I might be interested in them send me an e-mail

 

i'm going to eBay mine as to recoup the cost of the stock intake ($40), 2150 carb, pcv spacer ($ 60 for the pair), assorted gaskets ($30), carb cleaner ($3) and the paint and wire brushes ($10) I bought to recondition the manifold. The manifold s rusty and dirty, i'm going to hose it out with the hot soap at the car wash, and scrub the rust out and repaint it before I put it on the motor. I spent yesterday taking the 2150 apart and hosing out the jets and float bowl with carb cleaner, it was in great shape for a junkyard carb. I should get at least what I spent back on eBay.

 

what did you pay for the 2150? you putting a rebuild kit in it?

 

I really, really wanted the carb spacer that came with the carb, it doesn't have an EGR port, so no smog controls at all except for the pcv valve - but I had to buy them as a pair. I guess I'd sell the carb for $35. I didn't put a kit in it, it has a sticker on the side saying it was rebuilt by Holley.

 

I dont need EGR stuff. You offering to sell this carb? a 2150? send me a pic . Im interested. electric choke? AC solenoid? Is It Complete?