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Originally Posted by billrei
I thought one advantage of diesels is that they are relatively insensitive to the mixture ratio. To much fuel might cause a lot of blue smoke but I didn't think it would be responsible for the engine not starting. Of course I could be wrong, it's happened once in the past....I think....
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You are correct, Bill. The mixture ratio is not the issue. All diesels typically have much more air than they could possibly need.
The issue is temperature and heat. You start off with a stone cold combustion chamber which absorbs heat like a sponge. You must get the fuel above ignition temperature, in spite of this hugh cast iron heat sink.
Now, you inject fuel into the cylinder. The fuel, being somewhat liquid, also must be heated up to ignition temperature. Liquids suck up a tremendous amount of heat to raise their temperatures. Any liquid in the cylinder adds to the misery of trying to attain combustion temperature.
If you add too much fuel in there, there is no possibility of getting all that fuel up to ignition temperature and firing it off in a reasonable amount of time.
Reasonable is defined as the length of time your battery will provide to you for full cranking speed.
Personally, I would think it would be benefical to crank the engine for 5-6 seconds without any fuel (rack fully shut off). This would serve to rapidly increase the temperature in the cylinder because there is no liquid to heat up. Then, add a little fuel and light it off. I'd like to see someone who has starting issues with an older 617 try this approach. Of course, you would need to connect a separate Mityvac to the vacuum shutoff to attempt it.