Hi from Germany, I have big problems with a 1979 Bronco Engine and i need help with the 351M I cant get it running right, and also i cant get the ignition Timing right, to give you a picture Main Problem is Backfire under acceleration an hard Starting.
- Carb is a newer 2 BBl Holley 500 Power Valve ist Change from 55 to 85 Main Jets are Change from 73 to 71 because IT runs mutch to ritch.
- new Distributior,- new Dura Spark Elektronik Box
- new sparkplugs
- new Ignition wiring- new highPower Coil( Delete the resistor wire! )

I test the compression it's from 137 PSI to 153 PSI

The Engine only start with 15 degree early ignition, and only runs smooth at Idle if i put full engine Vacuum to the distributor Vacuumadvance ????

Than it runs realy smooth at Idle and i can read 18 HG steady in the Vacuumgauge, If i disconekt the Vacuumline i read only 10 HG that normal says to late ignition.

It Starts hard If it feels like it ignite before TDC an press on the Piston than.

But if i set it to 6-10 degree Ignitiontimig i get fuelblow out of the Carb???

With the high preignition it runs smooth and accelerate normal, If i press the Trottle to the floor without load it runs Like a dream but it stumbles and has backfire under load and acceleration when driving. I think the Problem i to early ignition, but with later Ignition i cant get the Engine Idle.
Fuel Level in Carb is ok, Idle Screws are 1 and 1 1/2 out, accelerationpump works.
Timing Marks on the Damper are not move, i Check that the 1 cylinder is realy in TDC position, Distributor ist not 180 degree off, it Shows 1 o Clock position at TDC

What the Hell is wrong with that Engine, i have no ideas anymore about????

Best regards
Torsten Hoppe
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9 volts to the coil for a Duraspsrk = yes
You DO need that ignition resistor wire with a Duraspark, unless you put an E-core coil on it like the newer ones had
Here is a pic of mine which runs a Duraspark and 12 volt Ford E core (40kv) coil
** Use a timing light
Verify the wiring roughly matches this diagram from a breakerless ignition tester box
You might need one of those diagnostic boxes do diagnose a no start someday
Post a pic of yours

 

Note that 1.1 ohm wire in the run circuit
Note the resistor bypass in the start circuit