Help with Timing, Vacuum and Backfire - 289c.i.

[agazzo]

HELP!
I really don’t know what to do, my 67 mustang is experimenting some estrange symptoms and I had tried a lot of things but they still.
First things first, my Pony is a 1967, Peruvian assembled, Hardtop (coupe) with a code C 289; she is with the family since new, was my mother daily car, she give it to me in October 1999, so I decide to make a complete Overhaul.
The body was repaired and beautiful painted (Dupond Candy Apple red) and the engine received some modifications:
- Overbored to 0.030
- Edelbrock Performer power package (Intake Manifold 2121, Lifters, 600 cfm Carburetor 1406, Valve springs, Camshaft 2122 – see below for specs.)
- Edelbrock fuel pump (1725)
- Manley Valves (1.940” Int., 1.600” Exh.)
- Ford 289 1966 Iron Heads, home ported
- Competition Cams Magnum Steel Roller Tip Rockers
- Pertronix Ignitor & Coil (Flame Thrower)
- High volume Oil pump
- Federal Mogul forged pistons
- Headman headers 1 7/8” & 3” collector
- ARP bolts and studs


After the rebuild and the cam break-in the car was used very few (100miles) and parked for two years (I am a consultant and got a job overseas that took a little longer than expected). When I return the first thing that I want to do was to turn on my car, so I begin to prepare it by changing the oil, but, oh surprise, there was water in the carter, a lot more than standard condensation. After the obligatory disassembly and a pressure test, I notice that the problem was porosity in the block, the last chamber in the driver’s side was leaking. In Peru, where I live, it is almost impossible to find a new block, so I decide to repair it. After an excellent welding job with the block immersed in sand or something like that, the porosity was gone, and I start the assembly.

When assembled, with 10° of advance the engine was running irregularly and making around 12” manifold vacuum, and building a lot of exhaust backfire. I try to correct it by modifying the timing, going after TDC until the engine make effort to start, in this way I got 28° ATDC idle timing, the engine was running better and the vacuum was around 15”; my total time, with disconnected vacuum advance, was of about 48°; too much for what I know.
I recheck the camshaft synchronism with the help of a degree wheel and was ok, with the 1 cylinder in TDC (top most piston position after the intake valve was opened and closed) and the degree wheel in 0, both dots where pointing each other in a strait line and, when assembled, the timing marks on the dumper where ok.
I replace the Pertronix Ignitor with a new set of points and condensator just to check if that so much advance was due to a defective Ignitor, and …it is the same, my engine wants 28° of idle advance.
I set the idle advance to 15° and try to regulate the carburetion, but it was impossible to get more than 1” vacuum and/or 20RPM more, I set it the best that I can and go for a ride. Once on the street, each time that I give gas the engine is backfiring through the exhaust, mainly when under load.
As a tip, my header gaskets are standard exhaust manifold ones and have being used twice (because of the leakage problem).

Now the Questions!!!
1. What should I do with the timing?
2. What about that silly backfire?
3. What about the vacuum?

I will appreciate any ideas or experiences.


Camshaft Specs.

Advertised @ .050
Int. Ex. Int. Ex.
Duration: 270° 280° 204° 214°

@ Cam @Valve
Int. Ex. Int. Ex.
Lift .280 .295 .448 .472

Centerlines
Lobe Seps. Intake Ctrline
112° 107°

Timing @ .050
INTAKE EXHAUST
OPEN CLOSE OPEN CLOSE
5° ATDC 29° ABDC 44° BBDC 10° BTDC