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Old 08-06-2016, 09:50   #1
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Throttle doesn't increase RPMs

Westerbeke 52 diesel engine. Ran fine during season in Bahamas. Back in Jacksonville for a month in a marina.

Took boat out today and engine does not go more than 2000 RPMs at full throttle. Throttle linkage appears OK.

I will dive on the prop later today to check for barnacles, etc.

Any other ideas I should inspect before storing boat for the summer?

Thanks for all suggestions.
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Old 08-06-2016, 10:27   #2
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Re: Throttle doesn't increase RPMs

Assume you have checked the fuel filters and other factors that effect fuel supply to the engine? If fuel supply is good then the prop would be the next thing I would check.

If anchored in a nice harbor in the Bahamas I might check the prop first.
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Old 08-06-2016, 10:34   #3
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Re: Throttle doesn't increase RPMs

I had my boat in a marina in Melbourne fl for 5 weeks. I couldn't get more than 2500 rpm out of a 3600 rpm engine. The prop was encased in barnacles a half inch thick. They grow fast in the SE. I'ld bet you find the same thing I did.
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Old 08-06-2016, 11:47   #4
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Re: Throttle doesn't increase RPMs

How high will it rev in neutral? If it revs higher that's more evidence pointing towards the drive train.
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Old 08-06-2016, 12:18   #5
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Re: Throttle doesn't increase RPMs

Does the propeller shaft turn easily with the engine in neutral? I had that problem and it turned out to be a melted cutless bearing.
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Old 08-06-2016, 12:22   #6
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Re: Throttle doesn't increase RPMs

Ooops! All these posts have been on the fuel and drive train side, including mine. The other side is a restriction in air supply, as in a clogged air filter.
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Old 08-06-2016, 14:22   #7
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Re: Throttle doesn't increase RPMs

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Originally Posted by FSMike View Post
How high will it rev in neutral? If it revs higher that's more evidence pointing towards the drive train.
Thanks for the suggestion. Engine easily revs to 2800 in neutral. Prop shaft spins easily. Cutlass bearing was replaced last fall. Will inspect more tomorrow during haul out. Hoping for an encrusted prop.
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Old 08-06-2016, 14:25   #8
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Re: Throttle doesn't increase RPMs

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I had my boat in a marina in Melbourne fl for 5 weeks. I couldn't get more than 2500 rpm out of a 3600 rpm engine. The prop was encased in barnacles a half inch thick. They grow fast in the SE. I'ld bet you find the same thing I did.
Thanks Bill.... I think (hope!) you are right. Haul out tomorrow will show what the prop looks like.
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Old 08-06-2016, 14:26   #9
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Re: Throttle doesn't increase RPMs

Prop shaft does turn easily. I will inspect the air filter. Thanks.
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Old 08-06-2016, 14:30   #10
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Re: Throttle doesn't increase RPMs

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Assume you have checked the fuel filters and other factors that effect fuel supply to the engine? If fuel supply is good then the prop would be the next thing I would check.

If anchored in a nice harbor in the Bahamas I might check the prop first.
I only wish i was in the Bahamas to check the prop! Unfortunately, I'm in the yucky St Johns River. Will inspect prop during haul out.
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Old 09-06-2016, 08:40   #11
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Re: Throttle doesn't increase RPMs

I have a 1998 Westy 82B4. It doesn't have an air filter, never did. I'd check the fuel filters (Racor and engine mounted cannister). You might also check to see if your fuel vent is clogged by listening to hear any suction air flow or if the RPM's increase under load when you remove the fuel fill cap. JMHO
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Old 09-06-2016, 08:49   #12
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Re: Throttle doesn't increase RPMs

Everyone has great thoughts & can all be a problem, but as a mechanic I always go with the most likely, definitely check the prop,a quick look to make sure nothing grew there (tells me you don't check yours enough, sorry) & at the same time make sure shaft is not bound, but honestly this screams of fuel restrictions. ...I have had filters that were not that old get pluged, that's next then the lines for a kink or something in there,,(don't blow air into the pump!) Been there,then it get serious if we are not by then,making sure you already have eliminated water in fuel........probably need to get pumps confirmed for pressure? ......... change filter, check for water in fuel, have fun
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Old 10-06-2016, 06:23   #13
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Re: Throttle doesn't increase RPMs

Thanks for your input. Yep, we neglected to jump in the dirty St John's River after siting a marina for a month to inspect the prop. What can I say, Florida is not our home turf! After boat was hauled, we definitely have barnacles on prop, not a ton based on stories from yard hands, but more than we've seen before. Fuel filters are clear, no water in racor filter, prop shaft good, etc etc. Getting the prop tuned and cleaned.
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Old 10-06-2016, 07:13   #14
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Re: Throttle doesn't increase RPMs

Glad to hear you found the problem. Since you're getting the prop tuned and presumably polished I'd recommend that you give your shaft, strut and prop a coating of PropSpeed. I know it's a bit pricey but its payback in performance and longevity more than make up for the initial cost. I've used it for years and it's been great both here in the warm waters of the Chesapeake and Florida as well as the cooler waters of New England. JMHO
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