Yanmar won't go beyond 2200 revs. Help!

[Hobiehobie]

I have a Yanmar 4JH3 DTE 2007 engine in my Hylas 54. Just made the trip from Ft lauderdale to Virgin Islands and on the way experienced some engine issues. The engine would not go above 2200 revs, and was slow to get there. And at cruising 2000 revs was using much more fuel than normal (1.62 kph rather than normal 1.1 mph). In neutral will easily go up to max 3800 revs. No exhaust smoke of any color, 1700 hrs. No noticeable unusual vibration, and at 2000 revs the engine sounds smooth and normal. The bottom is clean. No unusual vibration in turning shaft.

I know the prop pitch is 1 degree off of the recommended, but don’t think this could be the problem, and it has been that way for a while but this rev problem is new.

The only thing I can think of is something around the prop, but the diver was down scrubbing the bottom last week and would surely have noticed?!

I will dive on the prop once out of the marina, but what else could this be. What symptoms to look for? Fixes? Any ideas friendly knowledgable forum?

[Captain Bill]

You could have picked up a rope or piece of net on the prop. I was once 50 miles off shore and got a piece of polypropylene ripe around my prop. It was blue and i never saw it but my engine would only turn about 2000 rpm until I got it off. The ocean is full of floating trash, it's just something we have to deal with.

[a64pilot]

If the prop is clean, next exhaust elbow or fuel delivery, but I'm betting not clogged fuel filter, line, etc cause your fuel consumption is way up too.
My boat was severely overpropped when I got her, would only turn 2200 or so at full throttle, but still didn't smoke, my point being that not all engines blow smoke when overloaded, so lack of smoke does not mean your not overloaded necessarily.

[Hobiehobie]

Exhaust elbow is a new brass version. Prop is clean no fouling I just checked. If fuel supply issue why does the engine get to 3800 revs in neutral? What else can it be?

[hpeer]

My JH4 would not go beyond 1,600.
Forward, reverse or NEUTRAL.
Sent fuel pump out for service. They found it had a lot of dirt. Now like new.

[a64pilot]

Originally Posted by Hobiehobie

Exhaust elbow is a new brass version. Prop is clean no fouling I just checked. If fuel supply issue why does the engine get to 3800 revs in neutral? What else can it be?

In neutral you burn very little fuel even at high RPM, so a clogged fuel filter, line or weak lift pump will still supply enough in neutral, but not in gear.
However it could be all kinds of things, even a clogged air filter or anything that reduces power, I haven't seen a brass exhaust elbow before.

[boatbod]

Fuel restriction, possibly clogged filters and/or clogged lines/pickup plumbing, clogged vent etc.

First test is run the engine under load with a new engine fuel filter element and the fuel lift pump drawing directly from a jerry jug. If it runs properly, go back over the vessel supply lines and find the problem.

[J Clark H356]

Look hard at the prop. You say you are pitched one degree off. Do you have a MaxProp or other folding/feathering prop?

I had lower RPM (not anywhere as low as you) when my MaxProp got badly worn and went from 3600 to 3150. Had it reconditioned and now ok. If you are running unloaded at normal RPM, then prop or transmission is where I would look. Also look at injectors.

[boatbod]

It's not the prop, because if that was over pitched the engine would belch black smoke as the governor added more fuel to try to reach target rpm.

Similarly is unlikely to be the turbo for the same reason.

Short on rpm and no smoke or overheating means you have insufficient fuel and the engine is going as fast as it can, or there is a mechanical limitation stopping the fuel rack opening far enough.

[tdh1849]

Just a thought but call, " Complete Yacht Service" in Ft.Lauderdale, ask for the owner Mark ( Usmc). He is the Yanmar dealer in Ft.Lauderdale and will know what the problem is.

[Kita]

My first thought is with boatbod, fuel filter or vent or along those lines,but fuel consumption being up makes me think prop shaft may be bound up with fishing line or trash of sorts. Does prop spin by hand?

[Peter200]

Hi, had a simular problem with my 75hp turbo Yanmar would'nt rev beyond 2000 rpm, problem was the cockpit fuel shut off lever had come out halfway pushed it back in but it turned out the linkage on top of the fuel tank was 50% closed/open therefore restricting fuel flow. Cleaned up the linkage, WD40 some grease and now works a charm. Sometimes solutions to problems are more simple than we think. Good luck

[a64pilot]

It's a turbo?
If boost is down a turbo motor won't pull the hat off of your head, but they do generally blow black smoke, look to see if a hose is blown off of the turbo, that would cause your problem as well as a dirty turbo?

[JD-Odyssey]

I have the same engine and experienced a similar degradation in rpms. It turns out I picked up some bad diesel that clogged the primary filter. I don't know about you but it's almost impossible for me to determine my fuel consumption using gauges. I tend to use the gauges but balance that with a guestimate based on historical consumption at various rpms over time. Here's what I got out of my primary filter.

[Suijin]

I don't think it's a fuel supply issue...you'd not be burning significantly more fuel at 2000 than normal (with engine seemingly running smooth and normally) if that were the case.

Prop is free and not fouled, and I assume when you just checked it, if it's a folding/feathering prop it is operating properly.

How easily does the shaft turn in neutral? If you can't turn it by hand then you might have a disintegrated cutlass bearing that is binding. Would possibly explain RPM and fuel consumption. When was the bearing last replaced? If it turns freely, you might have a transmission issue, but I've never run into one limiting shaft revs that was not accompanied by telltale noise.

You did not mention what's coming out of the exhaust when under load running at 2000. Normal light grey smoke, or what? That would be helpful information. But the fact that at 2000 the engine is running "smooth and normal" but gulping fuel would suggest a running gear issue, not an engine issue.