1949 Chevy 3/4 Ton spark problem

The motor in my 49 Chevy 3/4 ton is a 235 cdi out of a 54 Chevy. The motor won't fire. I have strong spark from the coil lead to ground when I open the points. It is blue and it snaps a strong 1/2 inch plus but when I turn the engine over with the starter, the spark from the coil lead to ground is 1/6 inch weak. What the heck am I missing here? I have tried a different (used) coil and condenser but it does exactly the same thing. Why would we have such a strong spark when opening the points by hand and then nearly nothing when turning the engine over with the starter? http://www.chevytalk.org/fusionbb/images/smilies/laughing.gif

Not a converted to 12v truck? If not make sure the coil is a correct 6v coil, also if the battery is weak and the engine cranks slow, it draws current away from the coil. Make sure all the connections and wires to and from the coil are not frayed or have bad connections.

Not a converted to 12v truck? If not make sure the coil is a correct 6v coil, also if the battery is weak and the engine cranks slow, it draws current away from the coil. Make sure all the connections and wires to and from the coil are not frayed or have bad connections.

I don't think there is a resistor wire or block in the 6 volt system. The auto parts store hasn't got a listing for anything. I think it is start with 6V and run with 6V. I have found that the spark problem is intermittent, so I have purchased new ignition parts to install one at a time. I will be checking and cleaning up all of the connections at the same time. When I ran the jumper wire test to the coil, I removed the feed from the ignition switch to the coil. I achieved a good strong spark from the coil lead to ground but then it disappeared again, so I am going to start by replacing the points and condenser, and other major things. When I get it going with the jumper wire, I am going to clean and tighten up the wires and connections working towards the ignition switch and ammeter etc. There must be a major voltage drop or more in the system.
Thanks

I would check the coil resistance across the terminals. look for about 1.4-1.6 ohms.

I would check the coil resistance across the terminals. look for about 1.4-1.6 ohms.

The resistance was about 1.2 ohms on it and another old coil I checked. The resistance values between all the terminals were very close on both coils. I will compare the resistances to the new coil I have too.

:) I made up a new primary ignition feed wire from the +coil post to the distributor. The the primary ignition wire insulated connector that goes into the side of distributor (the points and condenser wire connect to it in there)was loose and dirty (not any more). I installed the new points and condenser. I have a good 3/4 inch blue snapping spark from the coil wire to ground when turning it over with the starter (hooray!). Because I installed the new wire, beefed up the insulated connector; installed points and condenser, all at the same time, I am not sure what the main instigator was, so I will venture to say that there was a voltage drop over that primary ignition insulated connector; I also suspect the points just because they were quite burned, and the condenser could have been adding to it.

The motor fired. I got it to run but had to keep priming it through the carb. The fuel pump is not delivering to the float bowl. Rot and mice have consumed major portions of both oil lines; I need to replace those before I can run the motor for any length of time. The water pump is leaking (not enough to stop me from moving the truck across the yard when I get the oil lines on.)

I still have the separate battery and jumper wire feeding the coil. I need to work my way back up the positive feed side of the power supply through the ignition switch and ammeter, to the main connection on the starter; making sure the connections are all cleaned and tightened, and that there is no missing wire insulation.

Unfortunately I didn't get any of those voltage measurements taken at the coil etc. while cranking the starter. I would have liked to have seen what the reading were too. Maybe we can get those after we get the second battery and the ignition jumper wire out of there.

I did not replace the coil, rotor, cap, or plugs.

IT'S RUNNING!

Great. I just finished doing a mechanical restoration on a 51 1/2 ton, for a customer. Make sure you have oil to the rocker arms, I have found on several of these engines the oil feed line in the lifter chamber was blocked starving the rockers.