Paging patrickt

[RUFdriver]

Patrick, you are the electrical guru on these Cobras, I need some help. I just got my UCC Cobra running, long story short the plugs were fouled black and the timing was FUBAR. BTW your info on the Holley zinc issue was very helpful… but I digress… cleaned the carb, changed the battery ,new fuel and finally got it to start and idle. Later while messing around with the timing ( I had to re clock the distributor as it was abutted against the thermostat housing…) it died. The 250 amp fuse at the battery switch was blown. All the wires seem to be ok, no obvious ground issues. Maybe the timing too far advanced putting too much load on the fuse??
Any thoughts?
Thanks
Doug

[patrickt]

Originally Posted by RUFdriver

Maybe the timing too far advanced putting too much load on the fuse??

No. Setting your initial timing at 10 degrees ATDC or 30 degrees BTDC is not going to change the electrical load on the battery, or the coil, or the MSD unit or the tail lights.... It will do other things, but not change the electrical load.

If you reclocked your distributor, are you absolutely positive you got your plug wires over in the correct order (and didn't move them in the wrong direction) and that you're not 180 degrees out? But even if you put the distributor 180 degrees out and mess up the plug wires big time you're still not going to change the load on the electrical system.

[patrickt]

Here's what I would do if you had the distributor out, the plug wires pulled off the cap and now the car won't run. Take the valve cover off the passenger side and watch your #1 valves. Watch the exhaust valve open then close as you rotate the engine from the crank bolt. Now watch the intake valve open. Keep turning on the crank bolt and when the intake valve begins closing, you will be getting closer to TDC so watch your balancer. Stop moving when it's about 30° BTDC. Make sure your plug wires are in the right order on your cap, and going in the right direction, and now point your rotor at the #1 plug. For now, disconnect all the electric leads through your ignition system and "hotwire" it so that the entire ignition system, which is just a couple of wires, be it points/condenser or MSD, is right in front of your eyes. Crank the engine with a remote switch on the solenoid and give it gas by manually moving the carb linkage with your hand. If there is nothing seriously broken in the engine, and you have spark, and you have fuel, your engine will fire up in two seconds.

[RUFdriver]

I “re clocked” the distributor by moving each plug wire clockwise one spot then turned the distributor CCW about an inch, this approximated the correct position of the vacuum advance unit ( 6 o’ clock). I never had to remove the distributor. This procedure worked and the car started right up. After completing this part the car wouldn’t re-start ( cranked really slowly) and fried the 250 amp fuse, that’s why I was thinking the timing went too far.

[patrickt]

Well, alright... just move one lead from the fuse holder over to the other lead and bolt it down (eliminating the fuse) and see if the problem is gone. I have never put a fuse on a starter motor, it's really not needed. In theory, I suppose a starter motor could fault to ground, but I've never seen one do so.

[patrickt]

Now, what will blow your fuse on the starter motor is if you have a low voltage condition on your battery and the fuse was sized so it just barely didn't blow when the battery was fully charged. On a starter motor, as the voltage goes down the current goes higher to make up for it.

[RUFdriver]

I ordered a 10 pack of 250 amp fuses for $10, what would we do without Amazon? The new battery is rated 800 cca, the old battery 760 cca, I can’t believe that extra 40 cca had anything to do with it. I suspect the way I hooked up the timing light in the engine bay “ may” have caused something to touch. Who knows. I’ll give it a try tomorrow too late to wake the neighbors now LOL

[RUFdriver]

I have been cranking on the starter the last two days, the voltage probably a little low even on a new battery.

[patrickt]

The only way you really know how many amps something is pulling is to measure it. An inductive ammeter is a wonderful toy to play with. And it will tell you things like the in-rush current on your starter. Here's a pic of mine drawing over 900 amps on the in-rush, and I do not have a special high performance starter. It's the same one Ford put in a zillion FE equipped cars and trucks.

[Tommy]

I've not heard of any reason for putting a fuse between the battery and starter motor. My main positive cable from the battery goes to the starter lug and from there through a high amp fuse to the rest of the car. I suspect that 250 amp fuse was near its limits and finally exceeded them after multiple starter engagements.

[eschaider]

OP, follow Patrick's guidance and remove the 250 amp fuse from the starter circuit.

OEM's do not fuse starters for a reason. Patrick's pic in post #9 is the best explanation. A good starter on a big block engine, on a cool morning (not winter) will easily pull the kind of amperage Patrick is showing when everything it in tip top shape. That's why starter cables are so huge.

If you use a 250 amp fuse in a circuit that is designed to operate at and can dynamically draw over 900 amps, you don't need to be an electrical engineer to figure out what is going to happen. Get rid of the fuse!

[RUFdriver]

I’ve never seen it before either, maybe it should be placed after the starter? I’ll have to trace the wiring and see what’s going where.

[Dominik]

You shouldn't even need 250Amp after the starter Maybe 50, depending on what you fuse.

I wired all my Cobras loosely according to a VW Bus from the 60s. Mainly because the wiring diagram was free on the web. I do advocate taking load off the ignition switch, via a relay for the starter.

I also kept the fans separate by feeding them directly from battery (fused), via relays. I activate by hand (switch to ground), but one might forget. A temp switch, in parallel, is good backup.

My last cars had a mechanical fuel pump, pre-historic points distributor and no wipers.
KISS, keep it simple, sexy.

[patrickt]

Originally Posted by RUFdriver

I’ve never seen it before either, maybe it should be placed after the starter? I’ll have to trace the wiring and see what’s going where.

On this one I'm with Dominik, I doubt you need anything, anywhere greater than 50 amps and nothing in between your starter and battery.

[eschaider]

Originally Posted by RUFdriver

I’ve never seen it before either, maybe it should be placed after the starter? I’ll have to trace the wiring and see what’s going where.

After the starter or before the starter does not matter. In the simplest terms possible it does not belong in that circuit.

[RUFdriver]

Why in the world did he put it in there? Oh well I’m not gonna worry, got a 10 pack of fuses for $10 on Amazon. May as well use em up!

[Jerry Clayton]

I don't remember ever seeing a 250 amp fuse anywhere on any vehicles---and pack of 10 250 amp fuses for $10??????????? are maybe the fuses 25 amp??

and another life experience with other peoples hot rodding-----do you have any stainless braided hoses?????????I have found them as a source for electrical miswiring many times as well as issues with shorts on carbon fibre mounted lights ---------

[patrickt]

Originally Posted by Jerry Clayton

I don't remember ever seeing a 250 amp fuse anywhere on any vehicles---and pack of 10 250 amp fuses for $10???????????

They're probably Chinese M-80's.

[RUFdriver]

Believe it
https://www.amazon.com/Skar-Audio-SK...7532650&sr=8-3

[RUFdriver]

The fuse probably has something to do with the battery location in the trunk.