Another no start - Crab Disy with points - Fixed!

glennpm

glennpm

Well-known member
I replaced my Pertronix recently with a rebuilt by Carpenter, original crab distributor. It was working very well until it wasn't.

I hadn't driven the 32 for a couple of weeks while I pulled and worked on my rear end and torque tube. I took it out for a spin and after only 3 miles it started missing and finally stalled out. I could get it going a couple of times but it wouldn't run and I had to get a tow back home. When it did ignite, it was like it was bogged. Pumping the gas would get it to clear a bit, boggy choking sound and then died. It refused to start at all once home

It presented as no or poor gas. So I started there.

- There were minimal fines in my clear fuel filter so I replaced it.
- Gas was quite low so added 5 gallons of fresh.
- Still wouldn't start and noticed that my fuel regulator was a little low so bumped it up to 2 psi. This is where an electric fuel pump is handy.
- removed the fuel hose just before its connection to the carbs and pumped about a half cup. It was clean and pumped well
- Gas was squirting out into the carb bowls with throttle.
- Starter fluid didn't even get hint of starting

Next I checked the electrics

- Checked primary and secondary ohms and seemed fine
- Temporarily installed a new Beru coil
- Checked continuity of negative connection wire to distributor
- Checked the condenser with a VOM and looked good, i.e., not dead shorted and when connected to 12 volts, it charged up to about 2 volts and slowly dropped voltage indicated on the VOM.
- Replaced the distributor cap with a new one I had
- With my timing light, I got secondary discharge from the coil to the cap but nothing for any of the spark plug wires I checked which was three of them

At this point I had confirmed that the coil was good but no spark to the plug wires. Aha, the only thing left in the circuit was the distributor rotor.I replaced it with a new unit that I had and it started immediately!

Bad rotor but why?


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Glenn
 
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My guess is that the rotor was leaking voltage to the center shaft of the distributor . . . that is about all I can think of. It doesn't appear to have anything wrong with it . . . but the voltage was going someplace.

What type of plug wires are you running - solid core or resistor? How about the plugs - standard or resistor?
 
Tim Ayers said:
By the looks of it, the carbon button is worn almost completely. Maybe giving you a weak spark?
Click to expand...


Hi Tim, The carbon button in the cap, with the coil wire connected, completes the plug circuit when the copper end of the rotor swings past the brass plug detents I believe.



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Look really carefully at the plastic underneath the spring steel part above where it sits on the shaft. You might see burn marks where the spark has gone through to the shaft. This happened to me once. You might see some degradation from underneath too. I "bulletproofed" my next rotor by putting a blob of epoxy over the centre part of the rotor where the previous one had failed.
 
Bored&Stroked said:
I've never seen a rotor with a carbon button - only the insides of the cap? :D
Click to expand...

Holy smokes and thank you for calling me out. Yeah, me either! That tang rides on the carbon button in the cap, not the other way around. LOL! Boy do I feel silly for saying that.
 
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glennpm said:
Hi Tim, The carbon button in the cap, with the coil wire connected, completes the plug circuit when the copper end of the rotor swings past the brass plug detents I believe.



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Click to expand...


Hi Glenn:

I'm embarrassed by my reply. I'm chalking it up to a brain hiccup. LOL!

Tim
 
Mart said:
Look really carefully at the plastic underneath the spring steel part above where it sits on the shaft. You might see burn marks where the spark has gone through to the shaft. This happened to me once. You might see some degradation from underneath too. I "bulletproofed" my next rotor by putting a blob of epoxy over the centre part of the rotor where the previous one had failed.
Click to expand...


Thanks Mart! One more for the "tool kit"
 
Bored&Stroked said:
My guess is that the rotor was leaking voltage to the center shaft of the distributor . . . that is about all I can think of. It doesn't appear to have anything wrong with it . . . but the voltage was going someplace.
Click to expand...


Mart and B&S, yes I found a tiny fault. There was some resistance, but not isolated!


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Bored&Stroked said:
What type of plug wires are you running - solid core or resistor? How about the plugs - standard or resistor?
Click to expand...


Resistor wires since I previously had a Pertronix and non-resistor plugs.
 
I would not run resistor wires as they really cause a lot of issues like this. The spark tries to find the easiest path to ground and resistor wires are like a big "clog" in the electrical path . . . all of a sudden, the spark finds an alternate path and once it does, it continues to use it.

You should see the difference in spark color and strength when you change from resistor wires back to solid-core wires (distributor machine). On most Harman Collins distributors, four of the 8 cylinders will misfire due to the spark jumping to ground in the yellow mid-plate. I've had to do quite a few "mods" to HC mid-plates to get the old ones to work with even solid-core wires.
 
Bored&Stroked said:
I would not run resistor wires as they really cause a lot of issues like this. The spark tries to find the easiest path to ground and resistor wires are like a big "clog" in the electrical path . . . all of a sudden, the spark finds an alternate path and once it does, it continues to use it.
Click to expand...




Thanks B&S, I'm buying new Cu core wires this morning!


I had an experience with "easiest path to ground" with my BMW motorcycle. I had a big project in building additions to the bike's frame to accept an articulated side car. I unplugged the two computers and removed and taped up the main ground junction attached to the frame. I needed to do several tack welds and did this to protect them.


After getting the bike back together i went for a short ride to check it out and it ran awful! I had un-taped the main ground but didn't reattach it to the frame ;-( The only ground path was miscellaneous lights, etc.


Glenn
 
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