Jere Lull wrote:

In article ,
Stephen Trapani wrote:


The motor starts hard, but instantly with a squirt of starter fluid. It
runs with a knock at almost all RPMs, but no knock at full throttle with
a little black smoke. After about 5-10 minutes, the power drastically
decreases. It will keep running in neutral, purring like a kitten at all
RPMs, however a fair amount of black fluid pours out of the exhaust, to
float on the water, not much smoke.


Sounds like low compression (hard starting) and injector mis-timing.

The black fluid is simply dissolved soot, which could indicate the need
for at least resetting valve clearances when you're not pulling
significant power. Could also mean a burnt valve. Either could cause
hard starting.

Looking again, the new head gasket would require readjusting the valves,
so make sure that's been done.

Using starter fluid is dangerous.

The hard starts could also be from undersized battery or cables,

Yes, I have a low battery bank. Old batteries and it turns over fairly
slowly. Once the engine is warm, it starts in a second or two every time.

or
slightly corroded connections. We have 1/0 and 2/0 cable runs of less
than 6' and can start with 11 volts. When we had smaller and longer
cables, it took at least 12v when everything was clean and tight. Years
ago, my car wouldn't start due to an extra ohm or two resistance in a
cable connector. Simply squeezing the connector in a vise fixed it for
almost 15 years (Mom's car).

The drastic power decrease after a few minutes could be a mostly-blocked
fuel filter, fuel tank pickup or vent. Change filters, clean the bowls
and see if it still happens.

I did this all once. Maybe the Racor needs changing? I had the tank all
the way out and cleaned by two mechanic friends.

Then open the fuel fill. If still no joy,
pull the pickup out of the tank and see if there's a screen at the
bottom.

I'm going to call him and ask about the screen at the bottom.... He says
no screen at the bottom.


Remove if there is. Once, I had so many dead critters in the
tank that a straight tube clogged. Siphoned the fuel out of the tank
through a Baja filter (West Marine has a good variant) to give the
filters a break. Luckily, we had less than 5 gallons onboard at the time.

I'd also suspect overheating at full power, except that the alarms
aren't going off. Any change in the reservoir level, day to day?

Reservoir?

If those steps don't solve it, I'm afraid you're looking at a rebuild,
but don't start worrying until you've exhausted alternatives, as that's
a remarkable engine from what I've heard.

Would a diesel needing a rebuild run hard for ten minutes, then lose RPM
and pushing power?

Stephen