Occasional loss of engine power on Hunter 356

Jun 21, 2016
24
Hunter 356 Annapolis, MD
The Yanmar 3GM30(f) on my Hunter 356 had its 1000-hour overhaul about 150 engine hours ago. It now experiences an occasional loss of power -- very occasional, three times in the last 100 hours. The engine rpms drop to about idle speed. If I close the throttle to idle, I can then speed it up to normal cruising speed, and it runs well for hours. I have checked the secondary fuel filter, thinking that there might be sediment in the bowl that gets stirred up and clogs the filter at at cruising speed, but I found it to be clean, with no sediment in the bowl. I have not checked anything else. Hs anyone had this experience and found the cause and a solution for it?
 

Rick D

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Jun 14, 2008
7,132
Hunter Legend 40.5 Shoreline Marina Long Beach CA
I think the first thing I would do is to have your tank cleaned and fuel polished. Sounds like the pick up tube is getting clogged with some debris. One opinion only. FYI, I had that happen and that was this issue.
 
Sep 25, 2008
7,076
Alden 50 Sarasota, Florida
Diesels need only fuel and air to run. Unless we are running out of the latter, it’s a fuel problem.

The list of guesses might include pick-up tube, bad fuel, bad pump, clogged injector, filter, etc....

Start with the easy stuff.
 

senang

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Oct 21, 2009
304
hunter 38 Monaco
+1 for the pick up mesh in the tank getting clogged. If the engine is pushing the boat at cruising speed it pulls an important flow of diesel through the mesh. Crud will accumulate on the mesh and obstruct flow. Over time the obstruction becomes important enough to influence engine performance. When you put the engine in idle less flow through the mesh, the crud falls of to the bottom. You push the engine again, cycle repeats ☹
 
Mar 6, 2008
1,078
Catalina 1999 C36 MKII #1787 Coyote Point Marina, CA.
Check primary filter input trap. Mine was 90% clogged with crud causing this same problem. It is easy to clean. I did not know there was a trap before the filter.
Visit Sail La Vie | 1999 Catalina 36 MK II to find out how to clean the trap.
Haro.
 
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Jan 7, 2011
4,727
Oday 322 East Chicago, IN
Tank vent plugged? My JD tractor would start stalling after about 40 minutes of operation. Happened several times I used it, and always about the,same amount of time. Turns out that the small air vent in the cap was plugged.

did it loose power on a longer motor?

Greg
 
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Jun 21, 2016
24
Hunter 356 Annapolis, MD
Thanks for all the advice. I will start with pick-up tube, then primary filter trap (if I can find it!). Regarding Greg's question, the most recent one of the power losses occurred about 15 minutes into a trip and then did not recur in the remaining five hours of cruising. I cannot remember the circumstances of the others.
 
Feb 26, 2004
22,760
Catalina 34 224 Maple Bay, BC, Canada
then primary filter trap (if I can find it!)
It's incorrectly called a trap. What it really is is a ball lift check valve.

It is only on the R24 and maybe R15 Racor filter housings.

Here:

 
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