Coil Wiring

KDL

KDL

Senior Member
This is for the truck in the avatar, 1936, motor is a 1940, fresh rebuild, helmet distributor rebuilt by Bubba, 6V positive ground.
I ended up going back to a remote coil, Echlin IC7 with a FA54 condenser, no resistor in the circuit.
I currently have the -6V from the ignition switch going to the + side of the coil and the - side of the coil going to the distributor. Do I have this backwards?
The truck starts and runs fine up to about 30 MPH then doesn't have the power I think it should have. Carburetor has been rebuilt.

Thoughts and suggestions much appreciated.
 
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A person can't be totally certain on coil polarity without a coil polarity tester but as a general rule the polarity would be backwards from a negative ground system. Pos+ would connect to the distibutor breaker points and the neg would be the power input from the switch.

The little coil testers are available from most of the resto parts sources but a graphite lead pencil can also be used. Refer to the link from youtube. https://www.youtube.com/watch?v=9eAHeKDelF0 The spark will jump to the pencil lead then flare a bit to the spark plug. If polarity is off, it will appear to jump from the spark plug to the pencil lead and on to the high tension lead in a reverse polarity.

An old analog volt ohm meter can also be used but not everyone has one of those anymore.
 
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If the coil has been ran with positive ground for any time the steel laminations will assume a set on polarity. Then when its reversed the coil looses a ton of reserve. Just for kicks wire it the other way and run it , wont hurt it and it may fix the problem..
 
Diagram of pencil test.
 

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Thanks for the input everyone. I replaced the coil and connected it with the + going to the distributor. The pencil test was inconclusive for me. With the old connection the flare did appear to be on the wire side. With the new coil it was hard to tell what side it was on. The truck still starts and runs good but the coil and wiring change didn't help the higher speed power. I'll have to keep looking.
 
There are a number of things that can affect the power toward the top end. Most carburetors have a power valve that has to function properly. The power circuit in the carb may be getting some crud in it. The fuel pump can sometimes not keep up with demand. OEM type diaphragm pumps can draw air in if there is any deterioration of the fuel line to the tank. The soft line from the pump to the firewall can crack and cause this. The fuel tank has to be vented to allow flow as demanded. If it can't vent well enough it might cause a problem.

On the ignition system,several things can cause problems. A bad coil or condenser can cause weak spark. The advance mechanism can get sticky and not allow full advance during acceleration. The vacuum brake piston can also get sticky or lose full braking action and not allow for retard under full power.

A combination of things can add up to poor performance and it makes it difficult to troubleshoot at times. Troubleshooting requires components that are known to be in good functional condition so a person might need to get some decent spares just to check things out at times. The engine cylinder compression readings also have to be half way decent to get good performance.
 
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Thanks rotorwrench. I appreciate your thoughts.
Everything on this motor is either new or reconditioned buy reputable builders. I understand that doesn't necessarily translate into operating correctly but one would hope so. It may end up being a drivetrain issue and not the motor at all.
I think my next step will be to get another set of eyes on this thing. Maybe that will point me in the right direction.
Thanks again. Every bit helps.
 
Not sure if I remember this correctly or not, but many many years ago my Dad used to use a slice of potato run the spark through it & see which side is scorched ?.
Maybe its me that's scorched.
Kpar
 
In the chassis & drive, you may have a dragging brake or brakes but you should feel it pull if that was the case. The rear axle or transmission could have a bearing problem but that would be easier to check by just hand rotating stuff.

When I troubleshoot, I start with the easiest thing first. If I had an early V8 with a helmet type distributor, I would get an original coil rebuilt by Skip check the ignition with OEM type parts that test good. I'm not a big fan of the adapters to the can type coils. Condensers are crap these days. I go through a few just to find a good one but I have a capacitor tester so I can do that. I also rebuild my own stuff when I can so that I can only blame myself when something goes wrong. The coil is the only thing I can't rebuild but Skip has one hell of a warranty so there is no point in even trying. Persistence pays off. You'll find it.
 
I have an OEM coil that was on the distributor when it came back from Bubba. I should send it down to Skip for rebuild. Maybe he also has a source for condensers.
I hope to spend some time on it this weekend to try to narrow it down.

Thanks
 
Skip will recommend a Echlin IH-200 from Napa. You will
need to use the round clamp that comes with the condenser
and use the long coil hold down screw on the passenger side
to clamp the condenser and ground it. Use a screw to connect
the terminal of the condenser lead to the brass tang on the
bottom drivers side of the coil. G.M.
 
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