Clark C500 SERIES:
1970 C500-45 cranks over but wont start

Its a C500-45 4 cylider LPG fuel. Had it 4 years, no problem at all. A couple days ago I hear it sputter a little but it didn`t kill, I used it a little more that day and it did it again then the motor killed at low idle. It took a few tries but it started back up, used it about 30 min with no problem, then tried to start it but would not start after trying several times. Pulled a plug and found no fire. I had a tune up kit on hand and I bought a new coil for it. Replaced coil, plug wires, dist. cap, rotor and points. Still no fire. Any help would be appreciated.
  • Posted 14 Feb 2019 15:07
  • Modified 16 Feb 2019 08:50 by poster
  • Discussion started by Kenneth
  • Louisiana, United States
Showing items 1 - 11 of 11 results.
Just thought I would check back in and thank for the help again and let yall know what the problems turned out to be. The wires of the condenser and coil wire were shorted out. After I got fire back to the plugs it still would not start. I sprayed some carb. cleaner in the air intake and got it to start and run shortly but it would not stay running but a second or two. Luck have it, one of my customers ace mechanics came to pick up a welding job I finished for them and he took a peek at it. He determined that initially I had a bad coil and fixed that problem when I replaced the coil but when I changed the points the wire connectors were connected on the wrong side of the insulator. The reason it did not want to start was because it was kind of cold that morning. He said the rubber diaphragm in the carburetor is very old and is getting hard and loosing its flex especially in colder weather and its getting worse as time goes by. He said until I replace the diaphragm I can use a light bulb or electric heater to warm up the carburetor diaphragm and it should crank right up. So far he is correct
  • Posted 28 Feb 2019 13:36
  • Reply by Kenneth
  • Louisiana, United States
Plus side of coil with key on I get 30 volts and while cranking I get a draw down to 25 volts and it holds steady at that voltage.
Neg. side of coil with key on I get 1 volt and while cranking I get a pulse from 1 to 2 volts.
Just out of curiosity I disconnected the neg coil wire from the connection to the condenser wire on the points and I now get 30 volts on that connection and at the neg. terminal of the coil.
With that wire still disconnected when I crank the motor it draws down to 25 volts and holds steady. On the positive side of the coil with the key on it does the same thing, I get 30 volts and it draws down to 25 volts and holds steady. I may need to replace the batteries in my meter or its not working properly because the voltage on my battery and so on should be about 12 volts. I will try again in the morning.
  • Posted 17 Feb 2019 04:07
  • Modified 18 Feb 2019 13:28 by poster
  • Reply by Kenneth
  • Louisiana, United States
Thanks mrfixit, I will try that
  • Posted 17 Feb 2019 00:51
  • Reply by Kenneth
  • Louisiana, United States
With the key on you should have 12 volts between the + side of the coil and ground. I think the pressure switch just turns on the LP fuel lock valve and the hour meter. If you have 12 volts on the + coil terminal, then check voltage between the other coil terminal (-) that goes to the distributor and ground while cranking the motor. It should be fluctuating between 12 and 0 volts as you crank. If it stays at 12 volts the points aren't closing due to gap or they are not clean or the wire is broken from the coil to the distributor. If it is 0 volts all the time while cranking then the wire is shorted to ground somewhere like where it connects to the points and condenser in the distributor.
  • Posted 16 Feb 2019 22:52
  • Reply by mrfixit
  • New York, United States
I jumped across the low oil pressure switch and the motor cranks but still wont start, so what does that tell you?
  • Posted 16 Feb 2019 10:41
  • Reply by Kenneth
  • Louisiana, United States
You need to see what you are getting on the + terminal on the coil.It should be battery volts. with the key on and battery volts while cranking. The oil pressure switch opens when there is no oil pressure.
Jumping across the switch tells you if the switch is good or if you have no or really low oil pressure. That's what feeds the + side of the coil battery volts.
  • Posted 16 Feb 2019 09:27
  • Reply by kelsey
  • Tennessee, United States
I used a volt meter and checked the wire that comes off of the top of the coil to the dist. and with the key in the on position I get 25 volts. The wire going to the points from the coil to the points is 1 volt with the key in the on position and when I crank over the motor it pulses from 1 volt to 2 volts. I have not seen any spark on the points while doing this and I have already tried different gaps in the points. I am at.025" gap on my points.
  • Posted 16 Feb 2019 09:01
  • Reply by Kenneth
  • Louisiana, United States
Thank you both guys. I have a question about the low oil switch. Will the switch not allow the starter to turnover or does it just shut off the fire to the coil if it is activated or malfunctioning? Like I said originally, the motor turns over just fine but I have no fire to plugs. Also I would like to know if I jump across the 2 terminals of the switch what will it do and what am I looking for? Will it allow spark to my plugs? Thanks
  • Posted 15 Feb 2019 14:50
  • Modified 15 Feb 2019 14:51 by poster
  • Reply by Kenneth
  • Louisiana, United States
That model truck came with a low oil pressure switch that opens the circuit between battery positive and the ignition side of the coil and the LP lock off valve. Check and make sure you have the proper level of engine oil. Then check the pressure switch buy jumping across it. The switch is located near the oil filter on the side of the head. it has two threaded terminals on it.
  • Posted 15 Feb 2019 01:20
  • Reply by kelsey
  • Tennessee, United States
Have you checked the voltage to the coil?
  • Posted 15 Feb 2019 00:10
  • Reply by BREWSKI
  • Nebraska, United States
Have you checked the voltage to the coil?
  • Posted 15 Feb 2019 00:10
  • Reply by BREWSKI
  • Nebraska, United States

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