I need help interpreting vacuum test results

[HOWDY69]

Resistance readings with no wires on the coil?

Yes, I brought it inside while it was raining

What coil do you have?

I will check with Tom tomorrow. He put it on when he built the engine.

Do you trust your meter to be reading right?

It is a one year old Craftsman and I keep it inside where it is dry and room temperature.
The voltage readings make sense but it is the first time I used the auto ranging ohm meter feature.
The primary reading wandered between 1.8 and 2.5 which seemed a little odd to me. I checked the reading again after the coil had come up to room temperature and it still wandered.

So I think that does it for the primary electrical system.
Battery...check
Alternator voltage...check
Ignition switch...check
Coil primary...check

Except for the Ignitor which is taking the place of the points and condenser. Not sure how to test it.

If I follow the Chilton troubleshooting guide the next step is to check the spark at each plug and read the plugs but they only have about 30 miles on the new plugs. Or I could skip over to the fuel side and learn how a carburetor works.

[Dragon]

Wandering ohms on the coil. First short the meter leads together and see if the wander goes away. If it does the coil has a problem maybe a loose connection internally. Lets say that is extremely rare like million to one. The terminals to internal wires are riveted or pressure soldered in the coil.

I have a Fluke 87V which is the top of that super rugged line and if I short my leads together on ohms it always reads zero. But on AC voltage it picks up the voltage in the air so it fluctuates a little bit. Like .005Vac

Cheap leads can cause ohm float as the resistance floats where they make the wire to end connections.

Don't worry about the spark plugs having several bad would be a hassle and very unlikely. If they are not oil soaked or completely black with carbon they are good to go.

[HOWDY69]

Wandering ohms on the coil. First short the meter leads together and see if the wander goes away.
Cheap leads can cause ohm float as the resistance floats where they make the wire to end connections.

Wow...leads float between 0.3 and 1.2 ohms. Could it be the battery in the meter?
Maybe there is a way to zero the meter I guess I had better find the instructions for the meter.
Although it seems like the coil is not the problem.

[Dragon]

I would look at the battery Ohms needs it but voltage does not need the battery except for the display.

[HOWDY69]

I tried new batteries but the meter still drifted. Pertronix sent me a long list of things to check. I will post an update after I have concluded my discussion with Pertronix.

[HOWDY69]

One of the tests Pertronix recommended was to measure the voltage between the positive terminal of the coil and ground. Prior to performing the test they said to connect a jumper wire from the negative coil terminal to ground. This is the same method Chilton recommends to test the ignition switch.

With the key in the on position I read a voltage of 5.5 volts which is below the Pertronix spec of 8 volts. If I disconnect the ignition wire and test the switch separately I read 10 volts through the switch. I am trying to understand why the readings are different. The reading goes to 10 when cranking or when the engine is running. The jumper has to be removed for the engine to run but it will crank with the jumper in place.

With the jumper wire in place current can go through three loops: the meter, the primary coil, and the Ignitor module. But they are in parallel so doesn’t the voltage across all three loops have to be the same?

[Dragon]

No the current goes through the least resistance. Before you read anything read the Bat + to - , What if all the playing around left the battery low then all your readings would be low. It does me no good to work on a low voltage light or outlet if the house is only getting 97 volts on one leg of the 240. Voltage does not pour through the meter. It has very high input resistance to stop it from effecting the circuit under test.

I bet Pertronix meant it had the negative wire to the dizzy removed. That way your test runs from the Battery to the switch and then through the coil. The voltage at the output of the coil should be almost exactly the same as the positive side. When you crank the engine the 2nd small wire on the solenoid bypasses the ignition switch switch and the resistor wire so it gets almost pure Bat + voltage. When the key is in run the power goes from the input side of the Solenoid to the switch to the resistor wire to the coil. In bypass the wire connects to the resistor wire at the end of it after the resistor. So they read different.

Always read the Bat then read the circuit under test. I will read the Bat and other times read the Bat + to the ground on the frame or body because I am looking for a drop in the Ground cable connections. I ground my engine, chassis body and Bat to one bolt on my rad support at the top of the passenger Fender. That way I can test any one of them for a grounding problem.

My truck wold get sick and die or the radio would get scratchy and cut out. Well all the little grounds all over the different places were loose and corroded so I moved them.

[HOWDY69]

I picked up a set of points etc. from Tom. I will know tomorrow if the Ignitor is the problem.

[Dragon]

According to Accel on their pointless system it works or it totally fails. I bet the dizzy module on the Pertronix is the same.

Does you Pertronix use an external module or is just in the dizzy. Hall Effect (magnetic systems) will fail weirdly if the magnetic field gets weak. But the transistor amp circuit is set as a switch and switch circuits are so range limited the fail they don't go weak they either switch or they don't. Optical ones just fail, the LED lights or it does not. The IR receiver just sees or it doesn't and it has the same switching amp circuit to signal the coil.

[HOWDY69]

The Ignitor is based on the Hall Effect. There are magnets in the donut. The only thing I have to go off of is the engine-off key-on voltage is out of spec (it is 5.5) yet the running voltage is in spec (It is 10). I have no idea what this means but I figured the best way to tell if it is the Ignitor is to put the points back in. I got the points for free and I need to know how to put them back in anyway in case the Ignitor does fail at some point.

Since I got the points for free I consider this a "test" and not a replacement so I am not breaking my newyears resolution.

[Dragon]

Have you asked Pertronix what the current draw is?

If your battery is at 14.2 and your resistor wire is 10 you have a 4.2V Voltage drop(VD). What that means is through all the wires through the switch and through all the connections there is that much corrosion, dirt, loose terminals and wore out switch. You have a severe loss. With my truck off I have 12.9 and my positive coil lead is 11.2.

I would bypass the switch under the dash by jumping from Bat+ to the ignition wire before the resistor. If the voltage comes up then you have a bad switch(dirty or worn contacts causing the resistance to rise.) Red/green stripe hooked to yellow wire at ignition switch. There are two connectors between the switch and the coil.

[HOWDY69]

Fuel pump pressure not vacuum and that is high we need 7 to 8 pounds on most carbs.

I tested the fuel pump pressure just before the carb inlet manifold (small chrome pipe bolted to carb). The pressure built quickly to 6.5 then stayed steady. When I stopped cranking the pressure bled down slowly over several minutes.

I removed the chrome inlet manifold and the inlet filters. The filters appeared clean except a very light discoloration of rust. The pores in the filter were not clogged there was just a dusting of the rust color here and there. This may have been from the steel fuel line between the fuel pump and the carb.

After the engine was warm I pulled the sight hole screws for the floats. The front sight hole dribbled a little bit then stopped. The back sight hole did not dribble. The fuel level appeared to be about a quarter inch below the sight hole.

This is as far I as made it today with the carb.

As I was messing around with the truck I would occasionally check the carb after I shut the engine off. When I looked down the primaries and pumped the throttle sometimes the fuel would shoot out the left side but only dribble out the right and sometimes it would dribble out both sides. How strong of a stream should come out when the throttle is pumped but the engine is not running?

[Dragon]

Raise the rear float level. It should shoot out the holes not dribble unless you were moving the throttle real slow. If the check ball is missing under the shooter you won't get a good squirt as fuel gets sucked out of the holes while the engine is running.

There is a problem with the accelerator pump circuit if all it does is dribble. This will cause it to stumble when you punch it.

6.5 is not bad unless you are racing then you would run out of fuel at higher rpm.

[HOWDY69]

I forgot to mention I put the points in today. It did not make a difference so I put the Ignitor back in.

I will read up on the accelerator pump circuit so I can check it tomorrow.

Do I need to be on level ground to adjust the floats? My driveway and street are somewhat sloped and my garage is occupied by the Mach1 in pieces.

The CCC guide talked about bench adjusting the carb first. I did not do that step. The carb was new when it was put on my engine so if they are normally good to go from the box mine should be ok.

[Dragon]

Pretty level both front and back and side to side. I never bench them unless I know that I am going to modify the carb for racing, rejetting, changing the pump size and so on.

Take your meter to a wall socket and measure it. 120 is the normal voltage and they are allowed but rarely below 115 or over 125 so that might give you a clue about your meter's real calibration.