Been trouble shooting a rough idle, low performance problem for a long while on my 312 in a 56 Merc with stock distributor. I hooked up a dwell, RPM.volt meter and noticed that the dwell increases as I throttle the carb. Is this indicating a bad distributor? Also, The volt meter is reading 7 volts. What should this reading be and is 7 a low reading?

Thank You - AR

It is most likely wear of the bushing allowing the clearance between the cam and points to change. As the internal bushing wears there can be increasing movement both up and down and side to side.

Where is the 7 volts taken? After the ballast resistor or before?

 
 Steve Metzger       Tucson, Arizona

Volt meter had one wire at the distributor side terminal of the coil and the other to ground. Thanks AR

Not too bad then - that test point is on the "down side" of the wiring harness, ignition switch, ballast resistor, coil primary .......plenty of rsistance ahead of your test point to drop the Voltage.

You probably have the "Load-O-Matic" distributor that looks like this under the cap? It delivers spark advance based on vacuum / air flow through the venturi orfice of the carb. If you have any leaks or stopages in that system - or a bad vacuum cannister on the dizzy - it can (and will) result in performance loss /over-heating / etc. The two visible upper springs and the "straight base points" are other ID clues.

If you have a bad bushing in the old distributor, it might be to your advantage to try out a "new" rebuilt from one of the auto supply houses. Ask for a distributor for a 1964 light truck with a 292.

 
 Steve Metzger       Tucson, Arizona

If you do get a later distributor you will have to update the manifold and carb to match.

55 Vicky & customline

58 Rack Dump, 55 F350 yard truck, 57 F100

59 & 61 P 400's, 58 F100 custom cab, 69 F100, 79 F150, 82 F600 ramp truck, 90 mustang conv 7 up, 94 Mustang, Should I continue?

Y-Block Bill! Even adding just the later distributor will make a big difference in the way it runs.I did change my distributor before I changed carb and manifold and really noticed an improvement in performance.You do need to find a source of manifold vacuum as you cant use the outlet on the stock carb.

  

If I remember correctly, Ted said in another thread that you can use the vacuum from the front of the carb for a later (57) distributor. The 56 has vacuum points at the front (ported??) and one at the rear (full, manifold, vacuum) which served the wipers, distributor and power brakes. Do I remember correctly?

54 Victoria 312;  48 Ford Conv 302, 56 Bird 312
Forever Ford
Midland Park, NJ

You cant use the one that worked with the stock distributor because its controlled by a  "spark advance " valve in the carb.

  

Your right! The original Carter thats on the engine has a vacuum port in the front that has a spark control valve that goes to the primary vacuum diaphragm on the distributor. At the rear of the Carter has a manifold vacuum source with a brass block that has two ports. One port goes to the secondary vacuum diaphragm on the distributor while the other goes to one of the vacuum assist on the fuel pump. Thanks for all the input - AR

Don't avoid the use of the later mechanical advance style distributor on account of a lack of a "ported" vacuum source on the carb - it can and will work just fine. Tuning is slightly different with the live manifold vacuum at idle (versus the ported) but the system will behave just fine on the road. When the throttle opens, the behavioral differences mostly disappear.......but the torque advantage of the mechanical advance version at lower levels of rpm is hard to overlook.

There are some articles (provided by our Mustang enthusiast brethren) that show the differences and similarities of the Autolite and Motorcraft versions of the Ford distributor - but not really much is found about the earlier "Load-O-Matic". You could re-bush it if parts are available and get everything back to original - it will just take a bit of effort.

http://www.mustangmonthly.com/techarticles/mump_0904_how_to_rebuild__autolite_motorcraft_distributors/index.html

http://www.mustangmonthly.com/techarticles/mump_0702_ford_mustang_distributor_rebuild/photo_17.html

 
 Steve Metzger       Tucson, Arizona