Vintage Tech Advice - August 2013
Beyond the Basics
One Horn Good, Two Horn Bad
I replaced the left-side horn on my '68 Mustang. I tried it alone and it worked OK. I then disconnected it and connected only the right-side horn. It worked OK. Then I connected both and they don't work. I can hear a faint clicking sound but nothing else. What might be the problem?
The horns are drawing more current than the vehicle's horn system can provide. One horn alone is OK but both together are too much.
This is actually a common problem and can usually be corrected by adjusting each horn. The horns have an external adjusting screw that should be turned slightly, in or out, until they work properly. A small adjustment—a quarter or half turn—should be all that's necessary. Avoid turning the screws in too far to prevent damaging the horn. I usually try the adjustment while the horn is activated so I can hear the sound change. I also like to annoy my neighbors…
We have a '70 Mustang powered by a 351 Windsor with a stock Ford two-barrel carburetor and PerTronix electronic ignition conversion. The engine has 6,000 miles on it since a rebuild to stock. The problem I have is that after driving the car seven to ten miles and shutting it off, the engine will barely turn over if I try to start it again. If I let it cool for 15 minutes, it starts right up. I have checked all the cables from the battery to the starter and engine block. I have gauges for temperature and charging; they show 205 degrees and 14.5 volts respectively.
Via the Internet
You are experiencing what engineers call a “hot soak cranking issue.” Once a warmed up engine is shutoff, its temperature will start to rise because the water pump and fan are no longer operating the cooling system. The temperature increase is considerable, enough to boil the coolant, therefore it is pressured by the radiator cap to raise the boiling point. During this time, the engine becomes harder to turn over, placing a higher demand on the cranking system. If there is any resistance or other issues between the battery and starter, they will show up during a hot soak start.
Assuming the battery is charged and large enough, I believe you will find a point of high resistance. A defective part such as the solenoid or battery cable—or simply a dirty mechanical connection—may show up during hot starts. The area of high resistance will most likely be warm or hot to the touch during cranking. Disable the ignition so the engine can be cranked without starting, then physically touch the cable connections as the engine is cranked. Be careful because a poor connection will get hot enough to burn you! This backyard method is obviously over-simplified but usually works. A voltage drop test is the correct method, simply done with an inexpensive volt meter and explained in any automotive shop manual.
Six Head Swap
I have already performed many of the performance enhancements to my '66 Mustang's inline 200 cubic-inch six-cylinder. I would like clarification that a '77 and later cylinder head with 1.760-inch intake and 1.380-inch exhaust valves can be ported and installed on my '66 block. I have already added a Pony Carburetors' Vaporizer carb, an '88 T-5 transmission, and a larger diameter '68 exhaust manifold. Would the addition of the '77-up cylinder head make sense for improving performance, especially with the '68 exhaust manifold? Or should I consider adding headers and a dual exhaust system?
Salmon Arm, British Columbia, Canada
The stock '66 cylinder head is much more restrictive than the '77-up head and should be swapped. The newer head has a much better intake manifold area.
The 200 cubic-inch six design is unique in that the intake manifold is an integrally cast part of the head. Most automotive engines utilize a removable intake, which can be replaced by a high performance unit. The Ford six requires a complete cylinder head change.
For now, I would install the better breathing cylinder head and continue to use the larger ’68 exhaust manifold. If a performance camshaft or additional carburetion is added, a set of headers and dual exhaust should be considered at that time.
Let us hear from you. Send your ’65-’73 Mustang questions to: Beyond Basics, c/o Bob Aliberto, P.O. Box 205, Salt Point, NY 12578. Send email to firstname.lastname@example.org.