53 flathead with 12v conversion. When in the run position I am getting 12v. When I go to start it drops to 4volts. What should the voltage be on start? Any suggestions why it drops to 4volts?

I have new distributor, points, cap, rotor, wires and coil.

Thanks

 

Is there a ballast resistor in the circuit, or does the coil have an internal resistor? Which post of the coil are you measuring at?

 

Positive to negative side and also positive to ground

 

Terminal-to-terminal on the coil is fairly meaningless, it shows the voltage drop across the coil if the points are closed, or zero if they are open. (+) to ground is what you want. It should be 12v unless there is a ballast resistor, you'll see more like 7v if there is a ballast and the points are closed. When the points are open, there is no current flow, therefore no resistance in the ballast, and you'll see 12v.

 

So why would I be getting 4v from positive to ground under starting?

 

What does the battery voltage drop to when starting?

Are you using a starter solenoid that has two big posts and two little posts? Usually those come as part of the 12v conversion. One of the small posts is labeled "I" and is mean to go directly to the coil (+) terminal, bypassing any ballast resistor, when cranking (only). The solenoids are Hecho in China usually and have a bad history of high resistance and poor quality.

 

It drops to 4volts. I have a coil with built in resistor. I didn't want to have an external resistor on the firewall. I have that kind of solenoid. So I should try to run the I from the solenoid to positive on the coil still? The only thing left to change in the whole system are the plug wires

 

If your battery voltage (measured at the battery) drops to 4 volts when cranking, you have a very dead battery, or a really bad starter.

No point running from the I to the coil with an internal resistor.

 

So, I got it to start one time. Now it just turns over and tries to start. Not quite sputtering. There are only 2 things I haven't changed. The starter or the gas. The gas smells ok. Could it be the carb? Will it start on ether like a newer engine would?

 

Check the timing first. Ether will work on any engine, but it isn't good for them.

 

Even with it starting and running for 20 seconds you think it could still be timing?

 

What Ross said in permalink #8. Have the battery charged and load tested. If it ran 20 seconds it is probably not your timing. If the timing is too far advanced, it will kick back.
Timing is always something you want right.

So what do we know about this truck? New to you? New after rebuild? How long since run? Tell us about it and listen to Ross.

 

Truck is all original except it has been converted to 12v neg ground. I just purchased it. I have been slowly working through the electrical systems. New battery, changed the bad solenoid. When I got it, it didn't turn over, due to bad solenoid. I have it turning over, so then checked the coil with multimeter, and it was bad. Replaced coil. At that time I did the wires and plugs. Now I have a strong spark. It started once and ran for 20 seconds after that. I turned it off ( it didn't stall ) and then tried to restart it and now it tries really hard to start but just kinda sputters with the starter engaged. I still have spark, but no idea why it won't run. I have tried ether but it won't run on that. Could it be the condensor? Am I not getting enough spark? Is there a sure fire way to check I am getting enough spark?

Starter engages no problems, but maybe it isn't strong enough to start it.

Little bit lost right now

 

Stock ignition? Has the condenser been changed to a 12v? They are different.

What has been done to the fuel system? Cleaned out, fresh pump and hoses? Has the carb been opened?

With a fully charged battery, and possibly even with jumper cables to another car that is running, give it a try. If the slow cranking persists and it doesn't start, I'd be looking at the starter first. I assume it's an original 6v starter? Please note, even on 12v, these don't crank like a modern car, they crank amazingly slowly.

 

I am thinking even with bad fuel and fuel system it would still run start on ether. Which it doesn't. Condenser has been changed. I am just wondering if it is timing, compression or not enough spark.

Does anyone know a good resource for mechanics in South Florida who can work on these?