engine issue? prop? nothing? help!

[donradcliffe]

Classic signs of a clogged fuel filter. Since the filters were recently changed, probably have a lot of gunk in the tank.

[degouwb]

I have the same issue when full throttle into head seas.
Tank is clean, filters are clean, pickup tube is clean.
I will check after spring launch on whether the rubber fuel lines may be collapsing .
The engine never stalls.....just drops to idle at the worst of possible times.

[Uplander]

Generally check the last thing you did..... "we recently changed filters, did full maintenance, and also replaced the exhaust elbows".

It is probably a fuel problem and I would check that the filters are properly seated. Also check for air in the system. Were they bled properly?
Good luck

[boatman1]

What clakiep (post #13) said: rubber fuel supply lines can start collapsing (especially at bends) and restrict flow w/o the poor mariner even noticing (until the engine loses power).

[JPA Cate]

Originally Posted by donradcliffe

Classic signs of a clogged fuel filter. Since the filters were recently changed, probably have a lot of gunk in the tank.

When we have had those symptoms, the above has been the cause. If your filter is gucky, time for a polish again, too. Start using biobor or similar.

Ann

[MCOS]

Originally Posted by donradcliffe

Classic signs of a clogged fuel filter. Since the filters were recently changed, probably have a lot of gunk in the tank.

Change the filters again. At least take out and inspect the element. Possible additional cause, a small leak in the line from the tank to the engine sucking air in when engine is under load or some blockage in the same line. Try pressurizing the line by hooking up a electric fuel pump or using an air pump to put a pound or two pressure in that line and see if it has any leaks.

[j.g.evans]

I had an engine that would die under load and even stop. After restarting it would run awhile. My problem turned out to be rust flakes from my iron tank that would restrict the pick up tube. When the engine stopped the flake would fall away. The flakes were too big to get to the filter so the fuel always appeared clean. My solution was to replace the tank.

[Compass790]

Originally Posted by clakiep

Intermitand fuel starvation under load. Check first : fuel lines specially the flexible ones with rubber inside, just change them as precaution. Than filters, gascolator, tank vents, and fuel contamination in the tank. Test if problem disappears after first item.

Capt. Claus - ocean tramp of the eighties

+1 for this.
I'd suspect an air leak as you've just changed filters. Check all the joints in fuel line.

[robgsailor]

Originally Posted by MCOS

Change the filters again. At least take out and inspect the element. Possible additional cause, a small leak in the line from the tank to the engine sucking air in when engine is under load or some blockage in the same line. Try pressurizing the line by hooking up a electric fuel pump or using an air pump to put a pound or two pressure in that line and see if it has any leaks.

We had a similar issue and the engine would rev fine in neutral. Under load, it wouldn't go beyond 2000 rpm and would drop.

We bypassed the fuel filter and all worked well. We were able to find a hairline crack in the fuel filter bracket by pressurising the fuel line.

[motretu]

an inexpensive diagnostic tool is a vacuum gauge, usually mounted on the suction side line of the fuel pump. there are a number of threads on how to use such a gauge.

[NorthCoastJoe]

As others have said fuel problems. Check for leaks at the filter housing. Being that you just changed filters you might have a bad seal letting air in. I would also check the crud in the tank. My Yanmar 3GM30 runs all day with the vent barely open so I think that's not likely the problem. ( ya I have a valve on my vent ) In both boats, I have a removable day tank so if it needs a cleaning its is easy to remove and clean. My original main tanks were full of crud.

Do you have a primary and engine filter? Both of mine are at the same level of filtration. Primary protects the engine filter.

[Searles]

Check the engine oil isn’t over filled ,a rough ride with over full oil ,may create windage ,just maybe .⛵️⚓️

[sailon46]

My money is on vent line maybe a kink that builds vacuum at high rpm.

[Denallan]

Fuel starvation.Had same problem on previous boat,fine at3000 in neutral,would slowly dropto 800 rpm in gear.After much searching found a mostly collapsed fuel line between tank and racor.The line looked new on the outside.You can test for blocked vent by opening fuel filler cap while experiencing the problem.You can also check for starvation by temporarily hooking up a spare outboard tank(with diesel of course) directly to your lift pump to rule out tank,lines,filters.I replaced my lines and never had the problem again.

[Airyella]

Thank you everyone for the replies. I checked the filters and saw no issues; topped up tank to almost full, added some seafoam, tested her in gear with the mooring lines tied astern to replicate some load, then headed out - no problems at all. We are due for a tank cleaning and polish but whatever happened the other day appears to have been related to the conditions primarily. Thanks again for the advice!