Yanmar 3GM Diesel Engine Hesitation

[ctva]

I'm looking for a wee bit of advice (aren't we all) on an annoying problem that highlighted it'self on out first outing last week after being ashore for the winter.

To set the scene... standard Yanmar 3GM30F with glass bowl filter in addition to the engine mounted filter and a plastic tank. Over the winter I cleaned out the tank, cleaned the diesel (about 45l) and then replaced it alongwith 80l of fresh diesel. checked for air on the engine filter bleed screw at which their was none. Engine fired first time and ran happily for 20mins or so. Launched. Ran again at tick over and with some power on the pontoon for an hour or so. No problems. Headded off next day into a F4 with engine happily doing 2600rpm pushing us alon at 6-7kts, sea flatish. After three hours, we cross the wake of a small ferry (big sharp wake) and a few seconds later the engine hesitates and loses power for a second or two (dropped a couple of hundred rpm). This then repeated it's self about two or three times more over the rest of the 10 hour trip but on flat water and for no reason.

Any ideas?

Many thanks for your help.

 

[Talulah]

My tuppence worth.

Somethings loose. The diesel/water seperator or fuel pipes are letting in air. The movement of the boat is causing the rubber pipes to move slightly opening/closing up the pipe connection.

 

[Fr J Hackett]

Fuel starvation somewhere in the system either an intermittent blckage or air leak, go over everything with a fine tooth combe.

 

[savageseadog]

Nine times out of ten it's air getting in. Otherwise blockage as above or the tank vent being bocked.