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Clark c20b won't starts and backfires
I'm having some trouble getting an old clark c20b running.

It was running ok but had some problems which need fixing. I replaced the head gasket, the muffler, fixed a break seal.

After putting everything back together it wouldn't start and backfired. I checked distributor had it 180deg out of time. I fixed that and got it to what I thought was good timing. It would turn over, but never start.

It is a LP system and you could smell some gas after trying to start it for a while. I pulled the front of the regulator/vaporizer off and when you pressed the by-pass button you to hear the gas come out.

I replaced the battery, coil, points, wires and plugs. It now will backfire consistently if hold the by-pass button down, but not start.

The lockout value on the vaporizer seems to be working (I can hear it click when key is turned).

Any suggestions on trouble-shooting?

  • Posted 6 Dec 2013 02:14 PM
Total replies: 5. Showing items 1 - 5 of 5 results.
It sounds like there is still a problem with the timing or the spark plug wires are on wrong.
  • Posted 6 Dec 2013 09:03 PM
Thanks. I am going to triple check everything again on the firing order and the timing.

Any advice on checking the timing? The info have is limited to the army manual. It it pretty much to find dead center mark and then adjust distributor to just be starting to fire on cylinder 1.

One item i keep checking on but always coming up with the same answer is the cylinder 1 is the rearmost cylinder.

Thanks again
  • Posted 8 Dec 2013 03:06 AM
Terms like "rear most" and such actually become meaningless unless you are present to point a finger at the "rear" you are referring to (rear of truck or rear of engine".
Engine terminology uses the crankshaft ends to define "front & rear".
The flywheel location identifies the "rear" of the engine.
Belt pulley/vibration damper identifies the "front" of the engine.
Cylinder number 1 is the cylinder nearest to the front end of the engine.
If you are only using the pointer on the vibration damper or pulley as the indicator for Top Dead [url removed] may be where you are messing up in aiming the distributor rotor.
Four stroke cycle engines must rotate through 720 degrees of the crankshaft (360 degrees for the camshaft) to make 1 complete operating cycle.
The marks on the damper or pulley will line up 2 times in one complete 4 stroke cycle of the engine.
To correctly use the marks on the damper/pulley as an indicator of TDC on the compression stroke you must also confirm that both valves on the timing cylinder (#1) be CLOSED when the damper/pulley marks line up.
If you have omitted to have cylinder #1 positioned with both valves closed when you install the distributor, you may have the ignition firing at 180 degrees "out of time".
Confirming that cylinder #1 is on TDC Compression stroke can be done by placing a thumb or finger tip over the spark plug hole and feeling for the onset of compression pressure while you "bump the engine" with the starter, or turn it manually with a bar. When you feel pressure against your finger, then move the crankshaft in the normal direction of rotation and line up the TDC marks.
Now you can drop the distributor into its hole and point the rotor at the #1 cylinder position on the distributor cap.
You will still need to fine tune the timing with a timing light later when the engine runs.
  • Posted 8 Dec 2013 03:46 AM
  • • Modified 8 Dec 2013 03:49 AM by poster
Thank you very much. That was it. Got it adjusted and running now.

  • Posted 8 Dec 2013 12:40 PM
  • Posted 8 Dec 2013 03:14 PM
Total replies: 5. Showing items 1 - 5 of 5 results.

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