back in the late 70's early 80's my uncle ran a john deere tractor. it had a decompression pedal, you held it down while cranking, until the engine got up to speed. my conclusion either they couldn't get enough amps to get the engine turning with compression, or they didn't feel the starter could reliably generate the horsepower needed. bottom line it took more power to turn the engine with compression. as for the starter,poor warm starts can be the starter but also a voltage drop due to a bad cable or connection. unless money is no object before you drop the coin on a starter, do the voltage drop test for both the starter positive and the ground side, and test batteries

 

The old John Deere used a gas put motor that was started with an electric starter. The little bout 5 HP gas motor turned over the diesel with the decompression valve plentifully was spinning and then you released and the flywheel got you through some compression strokes. These were 2 cylinder diesels and they crank at 800 rpm and pull top speed at bout 1100 rpm. I know, we had 2 of them.

So, some good observations in here between the bickering.
1. Diesels need to spin fast to start.
2. Initial starting energy on the diesel is higher due to compression ratio.
3. Once turning over, diesel is less hard to turn over but still significant. As the compressed cylinder does provide some push to help, but it is less than the energy needed to compress it due to frictional losses.
4.starter motors are best electric, as they produce instant high torque to get the engine moving.
5. Starting batteries are best for this job, deep cycle should be separated and maintained for longer slower draw loads.
6. Dual alts don't runt the same time, they are run one after the other, they are programmer by the GEM.
7 separate deep cycle for slower small loads should be isolated.


I am not getting into Jake brakes now, that's a wholenother list

 

jd actually used the decompression thing on newer tractors the one i was thinking of would have been late 60's maybe early 70's six cylinder and def electric start. a gas engine will pop and run even with virtually no compression, but the diesel, has to spin fast otherwise too much heat dissipates and there isn't enough heat to ignite the fuel. the old hand crank cars the magneto actually wound up as you were cranking and then just before TDC it would release like a trap, spin fast enough to actually make that first spark and get going. really old diesels started like that on gas and then once it was somewhat warm and turning quickly enough switched to diesel. some really neat old stuff out there