Clark C-20:
1966 C20B LP won't stay running

I have a 1966 C20B (Ser.# C20B 604 2054) that has run without issue for the last 15 years (that I've had it). Suddenly the other day, it wouldn't stay running...aka won't idle. It starts up no problem, and runs fine if given gas, but as soon as you let off the throttle it sputters out.
One thing led to another and we've done a pretty complete general maintenance update, as most components seemed virtually original. New hoses, filters, vaporizer and solenoid, plugs and wires, cap and rotor, coil, cables and rebuilt generator.

I'm wondering if maybe it's something electrical? The wiring has always been pretty wonky in this thing...in the sense that people have spliced and taped and pulled things out over the years it appears. But, as it's never had an issue, we've never bothered touching that aspect. I wonder now if something finally gave way perhaps.
I see all the old Clark manuals on their website, but they don't appear to have wiring diagrams in them.

I'm not that familiar with LP forklift mechanics, as I've been really lucky that this workhorse has never failed me in the least. Guess my luck has run out! Any clues would be appreciated.
  • Posted 22 Nov 2018 06:27
  • Discussion started by Vaulex
  • Rhode Island, United States
Showing items 1 - 2 of 2 results.
It's what we thought as well, but what is confusing is that it was used daily without issue, until one morning it simply started doing this. There was no gradual degeneration in performance in the slightest to make us think a gasket or diaphragm or valves had slowly gone bad or out of whack. Why we thought maybe something got yanked. Or when I saw the broken old hose I assumed it was some sort of vacuum issue, so I just replaced all the hoses. But it seems that's not a thing. Again, it starts fine, and unless you're flooring the gas, it simply dies out, which certainly smells more like a fuel thing.

But yes, we started with replacing the regulator/solenoid, with no effect.

I will try the carb mixture screw. I'm not sure what the secondary regulator is. Seems impossible to find any kind of shop or service manual for that thing, which I find a little surprising.

We having a running photo album of a random assortment of reference pics as we go along if you're curious to see the setup.

Thanks for the input.

https://photos.app.goo.gl/bkVJrhbLpyKcR8v46
  • Posted 24 Nov 2018 14:27
  • Reply by Vaulex
  • Rhode Island, United States
I doubt it is electrical, probably a fuel problem. Does that have the LP fuel regulator that mounts in the thermostat housing on the top of the motor? Did you replace that? If that is the type of fuel system it has, there may be a problem with the secondary regulator, that is the part that has the 2 flat diaphrams about 4' in diameter or it may have a carb with the diaphram mounted on it. Also, there is a idle mixture adjusting screw on the carb. It may be going too rich at idle. Try adjusting that screw.
  • Posted 22 Nov 2018 21:48
  • Reply by mrfixit
  • New York, United States

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