Originally Posted by arvicola-amphibius
Once up and running, it produces plenty of power, and no more black smoke than one would expect at wide open throttle. At 2200 to 2300 rpm it runs smooth with no smoke and pushes my 30 ft boat at near hull speed. After that first reluctant start of the day, it always starts easily enough without resorting to the Aerostart, unless it gets really cold again.
A local Yanmar mechanic reckons that these salt-water cooled engines commonly get corrosion in the exhaust valves, which means removing the head and getting the valves reground etc. But the compressions feel OK - at least I can hardly turn it on the hand crank unless I de-compress the valves. ?
Your compression is low. I know it FEELS OK, but Yanmars are finicky- anything less than 285-ish and it will start....eventually. The easy parts you can likely do yourself.
1. Start with taking off the "bonnet" and checking the valve adjustment.
2. If it's within spec, then check the cylinder head bolt torque. Tighten the bolts in the proper sequence.
3. Pull off the exhaust elbow and clean out the crud.
4. If still hard starting, bring on a mechanic to do a proper wet and dry compression test.
If the numbers prove out low compression, it's time to pull the head and see what is what. Could be valves, (culprit #1) or head gasket (culprit #2), valve stem seals (culprit #3) or it might be time for rings on at least one cylinder (less likely culprit #4).