yanmar problem getting high revs

J

JOURNEYMAN

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Hi,



engine has approx. 600 hours. out sailing today, motoring at 2000 rpm, comfortable. went to neutral then she would not rev higher than 1700. Tried in forward, reverse (I do have a longer term prob with low revs in reverse) and out of gear. the throttle control lever travels freely between low and high speed stops. 3/4 of way to high speed stop, no more revs come on - i.e. the last 25% of the travel has no effect. therefore I surmise that linkage is not the issue. Fuel is clean, all fluids topped up and clean. engine runs silky from low revs to 1700, no stuttering or misses etc.


this happened suddenly - there was no gradual loss of ability to rev, she would freely rev upto 3000 before today.



I'm perplexed and can find nothing in manual??



advice would be appreciated
 
Are you sure the cable hasn't slipped through the locking thingy at the engine? Can you rev the engine fully by operating the lever on the engine that the cable pulls on?

Edit: Apologies for the non-technical terms. :o
 
thanks tony, quite sure. the cable pulls the lever all the way to the stopper, so it is working OK. The issue is the engine revs up as the lever moves until it is about 3/4 of way to stopper. then it moves the last 1/4 to the stopper with no increase in revs. so I'm pretty sure the linkage is OK


PS, your technical terms are better than mine!!
J
 
Any work done to the fuel system that might introduce air or create an air leak; changing filters etc? If not it might be the governor has gone wrong.
 
Is it a GM Yanmar?
On these, the movement from the speed regulator lever to the governor lever is via a couple of small crank levers connected by 2 small tension springs. This mechanism is behind the cover-plate.
If the springs get stretched or damaged, this could give the problem you are seeing.
Possibly a bit unlikely, but I've no other suggestions.
 
its a JH4 HTE 110 hp turbo. No work done on fuel system of late. the fuel cut off is not, as far as I can see, linked to anything. ther stop button must cut the fuel some other way? My understanding is that the fuel cut off lever (sprung and next to the throttle lever) is just a manual stop mechanism if the electric one fails?? either way, the spring is tight and it is right on its stopper so looks Ok.

went for a spin thispm after checking everything and letting engine cool. achieved 2200 revs, so improving - but far from normal where 3000 available. maybe something is working its way through ... air dust ??

I'm scheduled form a long motor sail tomorrow into the teeth of a force 5 - this should test it out....
 
I presume you're not getting black smoke when you hit your current maximum RPM?

If no smoke, then I would think diesel bug - worth changing the fuel filters?
 
No black smoke. the prob is the same in neutral and in gear so not a prop issue. Interesting today we set off with engine running at 2000. I could get 2200 which is way below normal 3000. after approx. one hour, revs again reduced to 1600 and would not go higher. maybe the one hour thing is heat, guess it takes that long for engine to reach normal operating temp??

am going to change fuel filter tonight and clean air filter. would have thought bad fuel would cause spluttering etc. at 1600 she ran like a dream for 7 hours

J
 
Is this revving in neutral, or with a gear engaged? If the latter, sounds like a grubby prop. Quite likely at the end of the season.
 
well, winter is now passed. boat was launched and now she will start and run in neutral at tick-over revs for 4 or 5 seconds and then stop. have replaced fuel filters, cleaned lines from tank to engine filter, rigged a day tank with fresh today diesel, primed as per book and still no better. The fact that she starts and then stops points to fuel starvation. Also, to me implies that pump and injectors are OK (presumably if not it would not run at all if they were damaged). For the few seconds she does run, sounds sweet with no white or black exhaust. I reckon air is getting in somewhere ... but where? no discernable drips, leaks or damp bits .. any thoughts??

thanks

J
 
One thing that can fool many people is a partially blocked exhaust, sometimes caused by overheating the flexible exhaust by a water cooling blockage or starvation which causes internal delamination of the exhaust creating back pressure and limiting the revs. I expect you have confirmed that the exhaust is not restricted but a possibility in the event you have not.

John Lilley
 
JOURNEYMAN said:
thanks John, had not considered that. there is no visible sign of exhaust damage, how else could i detect such an issue?
Click to expand...

Not easy to detect externally as the pipe looks undamaged but you might detect localised softness relative to other parts of the pipe if the pipe starts to delaminate it separates into thin walled sections which fall into the core of the pipe making a form of flap valve.
You still get water coming out of the exhaust and all appears ok but in severe cases the engine will rev but will immediately drop to low revs and may not even be powerful enough to turn the prop at much above tick over revs,

The immediate thought is that it has to be fuel or a fuel governer fault, but if the governer is operating correctly and the engine can get enough air, then bear the exhaust in mind. I have seen engines replaced simply because this fault has been non diagnosed.

The only other unlikely possibility is that the timing has slipped, but not really likely.

John
 
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have you tried running it with the fuel tank cap off if the tank breather is blocked or the breather pipe perished it can collapse and cause a vacuum in the tank hence fuel starvation
 
I've been struggling with this same problem with my 4JH3 HTE for three or four years.

It comes and goes. The turbo has been checked and washed several times -- no problem. Fuel system is fine (tanks cleaned out every other year; dual Racors with vacuum gauge). The injectors have been replaced.

I had the injection pump off and sent to Panda for diagnosis -- checked out fine. Governor too.

Oddly, after that, it ran perfectly for a while.

Next thing I'm going to do is have the intercooler off and cleaned out -- apparently these do clog up from time to time, and I can imagine that this might be the problem.

Maddening. Let us know if you have a breakthrough.
 
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