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Old 09-08-2015, 14:59   #256
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Re: 50hp Perkins won't rev past 1900rpm

Definitely no need for any apologies your advice has been great and is very much appreciated.
I will take some prop measurements when the weather warms up here. It may be part of my problem but it will almost never revs over 1900 even in neutral so I think there is also something else at play here.

Regarding cleaning. I have soaked it in Hydrochloric acid and given it a good going over with wire ect. Itís come up ok but there is some bad corrosion on the water inlet tube where the hose clamps are placed. So that will need to be repaired. Today I will check the availability of the elbow and price. That will determine whether I buy new or repair.
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Old 09-08-2015, 17:02   #257
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Re: 50hp Perkins won't rev past 1900rpm

Good luck on your repair and we'll be waiting for a report once it's reinstalled. We're all curious here.

Your rev problem in neutral is not indicative of an over large prop but your doing hull speed at very low rpm is. As you try to increase rpm while underway your engine is working much harder at lower rpm when cooling water is not pumping as much volume into your engine and your engine isn't working as efficiently as it should be. So that's why it might be good to just check to see what your prop size is and compare it to what other folks have for your size boat and engine.
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Old 10-08-2015, 05:55   #258
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Re: 50hp Perkins won't rev past 1900rpm

Quote:
Originally Posted by d design View Post
Geez youd need one fancy tool to get to them unions!
sure would - a ring spanner and 8 seconds with a grinder, yessiree bob.
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Old 10-08-2015, 11:13   #259
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Re: 50hp Perkins won't rev past 1900rpm

Yesterday I looked up the hp rating of your engine. 42.5 hp at 2800 rpm. So if your engine is running at 1400 rpm you've got roughly 21 hp and less at the propeller due to slip.

You definitely need to get your rpms up so hang in there.
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Old 10-08-2015, 11:51   #260
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Re: 50hp Perkins won't rev past 1900rpm

I'm not familiar with a Perkins and I'm not sure if this has been mentioned in this thread, but when I bought my old Cape Dory she had a Volvo and wouldn't rev above 1200 or so. After looking through everything I was going to examine the injection pump. I went to release the screw which held the shutoff pull cable to the injection pump and when I loosened the screw the shutoff lever snapped down another 1/4 inch. Sure enough, the engine ran fine after that. I guess whoever had installed the cables didn't have the shutoff cable adjusted so that it was completely released and so it was always trying to shut off the motor a little.

Worth a check if the Perkins has a similar shutoff cable.
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Old 10-08-2015, 14:09   #261
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Re: 50hp Perkins won't rev past 1900rpm

Thanks Dave. We did look at this earlier. Turns out the engine has an electronic switch located on the back of the pump.
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Old 10-08-2015, 14:10   #262
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Re: 50hp Perkins won't rev past 1900rpm

Dropping the elbow off at a machine shop for repair today.
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Old 14-08-2015, 18:48   #263
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Re: 50hp Perkins won't rev past 1900rpm

I did some research but couldn't get a new elbow the same as the existing one. There where plenty available that could have been adapted to fit my heat exchanger. I received good help and advice from Luxfords Marine in Victoria (manufacturers of the heat exchange). The quotes where between $500 to $600.
In the end I got it repaired for the price of a bottle of Wild Turkey. Thanks Shannon, you are A legend.
Its not like new but its should last a couple more years and it's now firmly on my maintenance list.
Here are a couple of pics of the repair. Hopefully I will get it installed this weekend and will know if its been the cause of my problems??
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Old 15-08-2015, 22:36   #264
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Re: 50hp Perkins won't rev past 1900rpm

Well. Installed and tested. Couldn't get it to overheat but it did warm up so there may be a small improvement. The revs are still low.
Next step will be flushing the heat exchanger and checking that the tacho is reading correctly.
So what's a good way of cleaning the heat exchanger. Bearing in mind I have already bought some hydrochloric acid. So would prefer to use it if possible.
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Old 15-08-2015, 23:00   #265
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Re: 50hp Perkins won't rev past 1900rpm

My heat exchanger is different on the Mercedes so can't give you much help there. On mine I can take the rubber caps off the end and pull the core out and run a bristle brush through each tube.
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Old 17-08-2015, 10:26   #266
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Re: 50hp Perkins won't rev past 1900rpm

One other thing to check:

On my old cape dory the throttle cable assembly and shifting block had been replaced. The lever is one that controls the transmission as well as the engine. There is a button that you pull out or press in to engage or disengage the transmission control. I notice that when you disengage the transmission control on mine then there is a throttle blocking mechanism that slides into place to limit throttle movement, which limits the revs to around 2000 - 2500 or so.

Might be worth a check.
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Old 21-08-2015, 23:10   #267
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Re: 50hp Perkins won't rev past 1900rpm

Got 5 litres of Barnacle Buster. Here are some pics. I am currently flushing it through the salt water side of the cooling system at 4 to 1. I am planning to let this run for about 16 hours. Is this too long?
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Old 21-08-2015, 23:14   #268
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Re: 50hp Perkins won't rev past 1900rpm

It was quite easy to set it up. Hint. Take the impeller out if you want it to flow. .

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Old 22-08-2015, 21:51   #269
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Re: 50hp Perkins won't rev past 1900rpm

OK. Arrived back at the boat. Disconnected flushed with freshwater. And went for a test sail. Temp still getting to high.
Any thoughts?
I didn't take the rubber boots off then of the heat exchange. It could be possible that there is some crap blocking things. But wouldn't there need to be a significant amount of blockage tty of effect things? Or are heat exchanges a bit sensitive and precious.
I am also thinking about the thermostat. But if it was not working, then wouldn't it prevent hot water getting to the heat exchanger, with the result that the heat exchanger should remain cool.

Just so everyone knows. I did put the impeller back into the pump.
Here are some pics of bits and pieces that I am curious about. Also one of the temp Guage.

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Old 22-08-2015, 22:07   #270
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Re: 50hp Perkins won't rev past 1900rpm

Sorry about the rotation of the pic.

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