?? Double check voltage

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Jun 11, 2013 | 12:52 AM

halaferd

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?? Double check voltage

Ok just re assembled my 1951 flathead V8... Been at this for some time and think I've finally got it ready to run... But before I try in the morning I wanted to make sure my points were receiving the correct voltage. I've read several threads but just want to make sure I'm right.

The truck has been converted to 12V. I have a 12V coil. Hot wire runs to + post on coil, reading 12V, neg post reads 6V, and points read barely above 0.

NOTE I do have an external resistor between coil and points. When points are closed it reads 6V & 0.3-0V

When I open the points, all read 12V. 12V is to much at the points... Correct?

I feel like I've been here before, is there something wrong? Pretty sure I'm missing something.

Jun 11, 2013 | 12:57 AM

halaferd

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The coil I have is a 12V Napa 1307 w no internal resistor.

Jun 11, 2013 | 04:51 AM

big job

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Lets see if I can explane without a pic. 12vt + from the ign switch goes to one
side of the resistor the other side of the resistor goes to + on the coil. On the
coil side of the resistor a wire there goes to the second terminal on the starter
soliond so when starting that second wire shoots the full 12vts to the coil then
when running, it runs on the reduced voltage. Thats about it. done deal.

Jun 11, 2013 | 07:06 AM

ALBUQ F-1

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From: NM

When the points are open, there is no current flowing, therefore there is no voltage drop anywhere in the system. 12v everywhere is correct. All your numbers look right.

Jun 11, 2013 | 09:49 AM

halaferd

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Well it started this morning and ran for about 5min before I shut it off. A little blue smoke, some back firing through the exhaust, and wouldn't idle... But it ran on its own.

The only issue w the ignition is the ballast. It gets extremely hot to the touch. It is not wired like big job described. Only one wire to the coil, with 12V.

Jun 11, 2013 | 10:08 AM

halaferd

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Ok ran it again. Another 5-10min, smoke is nearly gone, along with back firing... Still will not idle, have to keep choke about 1/4 of the way closed and rpms up around 1000/11000. Have not checked voltage with engine running. I will do that next.

Jun 11, 2013 | 11:28 AM

CharlieLed

Lead Driver

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From: Brentwood, TN

Don't bother trying to check the voltage with the engine running, you cannot measure DC voltage on a circuit that is constantly changing. Everytime your points close current flows through the primary side of the coil. When the points open the magnetic field that was created in the primary windings collapses which induces a high voltage in the secondary windings (and the ferrite core) which leaves the distributor via the rotor/cap/plug wires.

Based on your previous voltage measurements I would say that your problem is not in the coil but more likely in the distributor (cracked cap, carbon arc, etc) or elsewhere as in the timing or fuel system.

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Jun 11, 2013 | 12:07 PM

halaferd

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I wanted to say fuel system... Timing is set, that part is for sure. As I posted earlier, I was unable to get it to idle. So I figured the power valve popped. Removed carb and as expected, there was fuel in the base and on the gasket. So I swapped the power valve for a block off. So to try and avoid this continuing until it runs for a while longer (clean it out & set idle)...

Well now it barely starts. Pump the throttle, fires runs very smooth for about 10-15 sec then dies off. Sprayed ether in the carb, to help isolate the issue, but it didn't fire... Really spinning my wheels here.

Carb is new, checked for any debris seems clean.

Checking fire at points, and double checking button position at TDC, and make sure plugs didnt fowl when power valve went.

Fuel pump is new, and feeding from a gas can that is clean and well vented... Could fuel pressure be an issue? It feels a little like it's starved for fuel.

Thanks for the help guys