Perkins 4.236 low RPM - SailNet Community

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Old 02-23-2014
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Perkins 4.236 low RPM

Hello fellow sailors


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, achieving only 5 knots. Most of the time the engine starts right away, (requiring rebleeding at 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. Engines feels smooth and doesn't get hot fast
It has 1100 hours ( almost new)

Yesterday 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 discovered 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 to the 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 02-23-2014
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Re: Perkins 4.236 low RPM

First, and easiest, is check the throttle linkage. Perhaps it is adjusted wrong on the pedestal or fuel injection pump, and doesn't move far enough.
I've had to take that pump apart on a bench (far from spares or a replacement) and I'm quite familiar with it's inner workings. There is a place inside where the tiniest piece of dirt will cause it to have a similar problem to what you are describing. If it's not the linkage, remove it (a wonderfully fun job) and take it to a shop and have it rebuilt. There is also a possibility that the injector tips are in need of replacement and if you are having the pump done, it can't hurt to do the injectors as well. I have also seen a Racor 500 plugged before the element, but you say the tanks were cleaned, so?
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Last edited by capta; 02-23-2014 at 08:55 PM.
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Old 02-23-2014
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Re: Perkins 4.236 low RPM

Don't forget to make sure the prop is clean and straight. A fouled prop can cut RPM's and speed way back. Of course this doesn't explain why you can only get 1500 RPM with no load.
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Old 02-23-2014
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Re: Perkins 4.236 low RPM

Two words: Mixing Elbow.

If fuel side checks out then the biggest culprit is likely to be plugging/carbon buildup in the mixing elbow where the RWC injects back into the exhuast.

Take it off and inspect it, if you can clean it, well and good, but be sure to check for corrosion and porosity before reusing it.
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Old 02-23-2014
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Re: Perkins 4.236 low RPM

Thanks Ron
That's a new one
I will check into it


Edwin
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Old 02-24-2014
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Re: Perkins 4.236 low RPM

I'll second the injectors and injector pump.. It'd not getting enough fuel. Those are super simple engines, it's most likely fuel delivery.

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Old 02-24-2014
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Re: Perkins 4.236 low RPM

Thanks

I will have an expert take a look


Edwin
Cal 46 Lahlia
MdR CA
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low engine speed , low rpm , perkins , slow speed


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