Engine Speed

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M

mattinva

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Aug 31, 2010
19
Hunter 290 Solomons Island, MD
I am having difficulty with engine speed. Recently, after hitting a fair size wave, my tachometer dropped from running speed of 3000rpm, to about 2100rpm. Throttle position appeared the same. Engine sounded normal, just the rpm was off. I advance the throttle to test if the cable, or linkage, had shifted. The engine did go faster, tach showed 3000 rpm, the throttle position was much further than usual, and black smoke was created. I have returned to normal position, with 2100 rpm. This weekend I confirmed with a laser tachometer that the tachometer is correct. The tachometer responds the same in gear, or in neutral. The engine is a Yanmar 2GM20F on a Hunter 290. Not sure where to go from here, i.e. fuel filters, air filters, injectors. Any ideas.
Thanks
 
kloudie1

kloudie1

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Nov 6, 2006
10,103
Hunter 34 Mandeville Louisiana
Black smoke means too much fuel for available air, or overload... assuming engine was running correctly before.. suspect something tangled in prop, air cleaner element, exhaust elbow..although elbow is more of a gradually building problem..
 
M

mattinva

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Aug 31, 2010
19
Hunter 290 Solomons Island, MD
I am confused why the throttle position would change, and what possible relationship with the large wave. It did create a good thump, hit it a little too square on. Is it normal for an obstructed air, or fuel, flow to change indicated throttle position relative to rpm?
 
anchorclanker

anchorclanker

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May 27, 2012
1,152
Oday 222 Beaver Lake, Arkansas
mattinva said:
I am confused why the throttle position would change, and what possible relationship with the large wave. It did create a good thump, hit it a little too square on. Is it normal for an obstructed air, or fuel, flow to change indicated throttle position relative to rpm?
Click to expand
Several questions with possibly the same answer. Something obviously changed abruptly, the test is finding the culprit. Anything that would cause the engine to lose power, would require an increase in throttle in an attempt to maintain the same power. An obstruction of intake air, a fuel issue, or some kind of fouling or mechanical failure downstream of the engine (prop, prop shaft, packing, etc..) could all act to reduce power/increase drag on the engine.

If the boat was slowed while under full power, the engine would be forced to slow down, putting maximum torque into the drive. Anything borderline could have failed at that moment causing the issue your having. If the engine appears to run okay in neutral, I would start at the prop and move forward.
 
M

mattinva

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Aug 31, 2010
19
Hunter 290 Solomons Island, MD
Engine operates the same in both neutral, and in gear. The throttle position used to generate 3000rpm, but now generates 2100rpm. I was thinking it might not be fuel since I can get black smoke at advanced throttle positions. Would intake air restriction cause the rpm's to be lower at a known throttle position?
 
kloudie1

kloudie1

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Nov 6, 2006
10,103
Hunter 34 Mandeville Louisiana
Matt.. yes.. The air element on the 2 and 3 gmf engines is notorious for degrading and making a restriction.. but anything else restricting air to the engine could do that .. strange that it happened on a jolt and has not "undone" itself.. have you opened the air box and looked?
 
M

mattinva

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Aug 31, 2010
19
Hunter 290 Solomons Island, MD
I have run for about 8hours since the event without change, or improvement. Air filter would be a nice solution, i.e. simple. I will take a look next time out. Thanks for the suggestion.
 
B

Blitz

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Jul 10, 2007
709
Seidelmann 34 Atlantic Highlands, NJ
Check your throttle cable at engine to be sure didn't slip and you are indeed getting WOT at the engine. Years ago that happened to me in a storm - not fun.
 
M

mattinva

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Aug 31, 2010
19
Hunter 290 Solomons Island, MD
When I adjust throttle position to 3000rpm, 80%WOT, black smoke. Presumably un-spent fuel. That day, before wave, I was running 3000rpm for hours. My fuel tank was at 1/8, and wonder if an air bubble could get in the fuel line. However, it has operated for 5 hours with no sign of distress excepting the lack of rpm's at known throttle position.
 
A

abaragones

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Sep 19, 2010
35
Oday 322 Glen Cove, NY
I would do two things (from your info regarding running engine with tank only 1/8th full)...bleed the system (at the filter and injector pump)...try it again...if not fixed then suspect a clogged fuel filter or pick up tube (maybe something in your tank got lose with that wake and was sucked)...good luck and let us know what was it when you fix it.
Abe
 
M

mattinva

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Aug 31, 2010
19
Hunter 290 Solomons Island, MD
Update. I checked the air box. If there was foam in the air filter before, there isn't any sign any more. Not even a scrap, makes me wonder if it was removed before I purchased it. If I can confirm that a 2gm20f is supposed to have a foam filter, I will purchase a new one. However, that will probably not fix the problem as that will only limit the air further. I will change the fuel filters next, but not very hopeful as I can get black smoke indicated too much fuel.
 
sling

sling

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Apr 30, 2012
9
hunter 33.5 kehma
I have a 33.5 with the same motor and I can't get it to 3000 rpm. when I tried to fills like I'm gonna break the throttle
 
kloudie1

kloudie1

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Nov 6, 2006
10,103
Hunter 34 Mandeville Louisiana
Yanmar Air Filter

mattinva the filters are notorious for turning into poly sand and flowing into the engine .. here is a shot of my last one .. I now have a good grade of open cell air filter foam on that core.. I don't think that is your problem..
 

Attachments

onecoolair

onecoolair

.
Jun 25, 2012
942
hunter 356 Kemah,the Republic of Texas
mattinva said:
I am having difficulty with engine speed. Recently, after hitting a fair size wave, my tachometer dropped from running speed of 3000rpm, to about 2100rpm. Throttle position appeared the same. Engine sounded normal, just the rpm was off. I advance the throttle to test if the cable, or linkage, had shifted. The engine did go faster, tach showed 3000 rpm, the throttle position was much further than usual, and black smoke was created. I have returned to normal position, with 2100 rpm. This weekend I confirmed with a laser tachometer that the tachometer is correct. The tachometer responds the same in gear, or in neutral. The engine is a Yanmar 2GM20F on a Hunter 290. Not sure where to go from here, i.e. fuel filters, air filters, injectors. Any ideas.
Thanks
Click to expand
Saw your posting last week.....This just occurred to me. Did you check the key way on the prop. Your prop could be spinning on the end of shaft. And the nut may are my not still be there.
 
M

mattinva

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Aug 31, 2010
19
Hunter 290 Solomons Island, MD
Tach acts the same in gear as neutral, so I was thinking it was not prop related.
 
onecoolair

onecoolair

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Jun 25, 2012
942
hunter 356 Kemah,the Republic of Texas
mattinva said:
Tach acts the same in gear as neutral, so I was thinking it was not prop related.
Click to expand
Hmmm?..So no loss of knot speed? Sorry misread your post. In that case check your alternator. Your tach gets its voltage from alternator. Which will cause it to miss read or not work. There could be a bad connection to back of alt or a sign that your alternator is fixing to blow the regulator diodes. One way to tell is do you hear a rapidly clanking/ hammering back and forth sound coming from alternator. Listen carefully because sometimes its hard to hear over the sound of diesel. My tach did that just before alt failed and started smoking.
 
M

mattinva

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Aug 31, 2010
19
Hunter 290 Solomons Island, MD
I verified tach with a laser tachometer. It appears to be functioning. +/-100rpm
 
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