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Old 02-24-2014, 12:06 AM   #1
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Default Perkins 4.236 low RPM

Thx to the internet I get tips advices and help on how to trouble shoot and fix problems

This time I have a new problem with my 1968 perkins 4.236 85 bhp engine in my cal 46 sailboat, Lahlia which hails at Marina del Rey CA


I seem to remember that I was able to rev my engine passed 1500 rpm before

Recently it'd only go to 1000. The engine starts right away, ( required bleeding a number of times) No black or white smoke. It runs smoothly. No water in the oil. It's not burning oil, no funny vibrations. Sounds great according to visitor engineer
It has 1100 hours ( almost new)

I had replaced my secondary fuel filter fearing ( on someone's suggestion) that I had reversed the O ring placement on the engine-attached fuel filter.... That was okay

But I did discover that the O ring on the primary Racor 500 had been TWISTED. After this rectifying this and After bleeding the engine, I ran the engine to 180 F temp and I was able to reach 1500 under no load ( while at dock)

My stainless steel fuel tanks have been cleaned 5 years ago. The auxiliary
Electric fuel filter is clear and the fuel looks sparking clean coming out of the Racor before it feeds into the engine

When I ran my auxiliary fuel pump it puts out fuel readily indicating there is no impediment
Or obstruction of flow from the hoses and fuel tanks, which contain biocides and stabilizers

Does anyone know why my RPM is not reaching maximum? And how can I rule out
Problems with injector pump or perhaps lift pump

Thanks in advance

Edwmama
Cal 46 Lahlia
MdR CA
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Old 02-24-2014, 12:56 AM   #2
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As I pointed out elsewhere -- I'm not a mechanical engineer, but this sounds very similar to a problem that the previous owner of my boat mentioned to me, triggered by your comment "lift pump".

The fuel tank on this boat is under the engine and goes way down into the keel. Even at a reasonably high fuel level the small electric lift pump didn't have enough grunt to lift the fuel from the tank and feed it into the injector pump with sufficient pressure, so the engine would idle but do no better.

The solution was to install a day tank into the engine bay and a higher capacity fuel pump (just a Johnson brand all purpose pump) into the engine bay with it to pump 25L of fuel at a time from the main tank into the day tank.

The way you can rule this out as a problem is to fill a diesel cannister with fuel and run the input line from the lift pump into the fuel can, placing the fuel can at different heights (alongside and above the engine) to see what results you get.

Option 2 is just to replace the lift pump but with some engines that's not so trivial.
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Old 02-24-2014, 03:05 AM   #3
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Default Perkins 4.236 low rpm

Thanks for you kind response delatbabel

I will do research on day tanks

Thx again

Edwin
Cal 46 Lahlia
MdR CA
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Old 02-24-2014, 01:48 PM   #4
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You might also find this thread useful:

50hp Perkins won't rev past 1900rpm - Cruisers & Sailing Forums
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