Engine Won't Idle Under Load

[Tiki 38']

I have a yanmar 3GM30C that will not idle under load. Like in gear at idle, the motor will struggle then stop. Even using the alternator at idle will kill the engine, such as using the electric anchor winch. Does anyone have an idea what could be causing this problem? I have cleaned out the fuel lines/filters but this made no difference.

[Sailmonkey]

what speed are you trying to idle at? it may be too low to allow the engine to compensate for an increase in load.

[Ex-Calif]

When that happened to my boat I found a polyprope line around the prop...

[neilpride]

Some debris around prop, a line or something?? some one touch the idle setting in the governor?? what rpms you have in the tach at idle??

[Tiki 38']

I have tried a fast idle, it made no difference. Once the engine is fully warmed up it will not idle at all, unless I increase the throttle.

[Sailmonkey]

1. how many hours are on it?
2. if you can get into gear without dying will the engine come up to speed while pushing the boat?
3. have you tried to disconect the alternator and run in gear?

[Tiki 38']

Hours unknown. Yes I can get into gear and quickly get revs up and engine pushes boat fine. It is the idle that has no power. Engine goes good at mid to high revs. Have not thought about disconnecting alternater. That is good thinking, might be something in that. Alternater is brand spanking new. Thanks guys for the replies so far, really appreciated.

[Sailmonkey]

I'm having a thought about the alternator. What size is it? internal or external regulator? size of battery bank you're charging? state of battery discharge?

[Stillraining]

Something is amiss with your governor.

[Chief Engineer]

1 Check Prop

2 If you have put a new alternator on....that might be your problem right there.
Disconnect alternator and try idle in gear.

3 Probably not the governor unless someone has been messing witht the injection pump

4 If you have played with the fuel system bleed again from primary filter to injectors.

[Ex-Calif]

Anyonr tightened the packing gland recently? Is the shaft hot while running? Is neutral idel the same as it was?

[meyermm]

Unknown hours! engine lacks torque, needs to be run at high rpm. I think the alternator is the least likely, start with a compression test and if reasonable fuel pump and injector area. Check tappet clearance before doing compression test you may even find the problem is that easy, maybe.

[Tiki 38']

Thanks for your time fellas, next time I am at the boat, tomorrow hopefully, I will take the belt off the alternator and run it to see if there is any difference. It is a new alternator I just had fitted because I was fed up with flat batteries and poor starting. Last time I used the engine, it unexpectadly chewed up the belt, so there could well be something wrong with that alternator. Pity, cause it was expensive too. I will dive over and check that prop, but I don't think so, as the engine dies with just useing the anchor winch. Then again mabee I have rope round the prop AND faulty alternator! Could be two things! What a great forum this is....

[Tiki 38']

O.K. Will do that too! I have just bought this boat, and I paid for a mechanic to do an engine inspection before I bought it (including a compression test), but he did a really poor job of it, cause I have had nothing but trouble with the engines since day one.

[meyermm]

The problem with the alternator could be that it works and the old one did not hence added load that the worn out engine needing service cannot handle. Sorry but prop problem would not cause out of gear cut out due to load from alternator.