Mercruiser 3.0/Alpha I; gradual loss of RPM at WOT
 

Engine is remanufactured, installed 4 months ago by the boat's prior
owner. Has ~5 hours on it, all by me. Previous owner didn't winterize
original engine properly, destroyed it, had it replaced, sold boat to me
two weeks ago. Engine is still under warranty, so I'm going to have the
installing dealer fix it, but I'm still keen to see what you *people*
think. (Was going to say "you guys", but I didn't want JimH to get
offended by not being included. Not sure "people" covers it either, but
that's another thread...)

Symptoms are as follows: at any throttle setting up to about 4000 (WOT
range is 4400-4800), the engine runs smooth as can be. If I push to WOT,
it moves right up to 4800, boat gets to 37 or so, and after about 10
seconds the RPM will slowly drop. I can hear the engine knocking when
this happens (there is also a valve-lash-type ticking sound,
intermittently, at other times, but...another thread).

I've let it drop back to 4000 or so, but throttled back before any other
symptoms manifested (I've read old threads here about backfiring and
stalling - didn't get any of that).

I'm a fairly capable auto mechanic, and my first thought is fuel
starvation. Something like a float bowl emptying at WOT and the fuel
pump not keeping up.

Any other ideas are appreciated.

Could be fuel flow or timing set wrong.

"Mike D" wrote in message
news:plgte.945$Zt.839@okepread05...
Engine is remanufactured, installed 4 months ago by the boat's prior
owner. Has ~5 hours on it, all by me. Previous owner didn't winterize
original engine properly, destroyed it, had it replaced, sold boat to me
two weeks ago. Engine is still under warranty, so I'm going to have the
installing dealer fix it, but I'm still keen to see what you *people*
think. (Was going to say "you guys", but I didn't want JimH to get
offended by not being included. Not sure "people" covers it either, but
that's another thread...)

Symptoms are as follows: at any throttle setting up to about 4000 (WOT
range is 4400-4800), the engine runs smooth as can be. If I push to WOT,
it moves right up to 4800, boat gets to 37 or so, and after about 10
seconds the RPM will slowly drop. I can hear the engine knocking when this
happens (there is also a valve-lash-type ticking sound, intermittently, at
other times, but...another thread).

I've let it drop back to 4000 or so, but throttled back before any other
symptoms manifested (I've read old threads here about backfiring and
stalling - didn't get any of that).

I'm a fairly capable auto mechanic, and my first thought is fuel
starvation. Something like a float bowl emptying at WOT and the fuel pump
not keeping up.

Any other ideas are appreciated.

"Woodchuck" wrote in message
.. .

Could be fuel flow or timing set wrong.

Its not "timing" - it would ping/knock on instant application of WOT.
but in 10 seconds at WOT, you;d drain the carb bowl enough for it
to go lean, so yeah, I'd say fuel filter, fuel pump, etc. Start w/ filter.




"Mike D" wrote in message
news:plgte.945$Zt.839@okepread05...
Engine is remanufactured, installed 4 months ago by the boat's prior
owner. Has ~5 hours on it, all by me. Previous owner didn't winterize
original engine properly, destroyed it, had it replaced, sold boat to me
two weeks ago. Engine is still under warranty, so I'm going to have the
installing dealer fix it, but I'm still keen to see what you *people*
think. (Was going to say "you guys", but I didn't want JimH to get
offended by not being included. Not sure "people" covers it either, but
that's another thread...)

Symptoms are as follows: at any throttle setting up to about 4000 (WOT
range is 4400-4800), the engine runs smooth as can be. If I push to WOT,
it moves right up to 4800, boat gets to 37 or so, and after about 10
seconds the RPM will slowly drop. I can hear the engine knocking when
this
happens (there is also a valve-lash-type ticking sound, intermittently,
at
other times, but...another thread).

I've let it drop back to 4000 or so, but throttled back before any other
symptoms manifested (I've read old threads here about backfiring and
stalling - didn't get any of that).

I'm a fairly capable auto mechanic, and my first thought is fuel
starvation. Something like a float bowl emptying at WOT and the fuel
pump
not keeping up.

Any other ideas are appreciated.