Decompress for what again?

[alex8]

Hi,

Many of you have helped on my prior quest to re-start my Yanmar after adding fuel (refueling 20gm20f), leading to success after bleeding the system and my great gratitude. During that time I learned that many people run the starter to crank a few turns with the decompression levers on, in order to bring oil to the cylinders in a cold engine before high pressure operation. I tried to do that but instead of cranking all I got a was a whirring sound as if only the starter motor was working. Is that what it' supposed to sound like with the decom levers on? When I then tried to start with them off it wouldn't start, alhought the batteries were low and the engine had not been warmed due to a drop light in engine burned out. Any insight into this decompression (do it, don't do it, what's the sound, etc?). Thanks again in advance for any assistance on this.

Alex

[Badsanta]

Yes. That sound is normal. With the levers up you have no compression so the pistons et all turn real easy. You stated that the battery was low. That is a problem. That yanmar has no glow plugs so you have to have a fast strong crank to get the compression to make the heat to to fire the diesel. When you try to start give it 3/4 power and prepair to reduce it as soon as it starts. It wont start with a slow crank because of a lack of compression heat and fuel.