Lister LPWS4 Hunting at one throttle setting

[Jess--]

I'm not on the boat at the moment so am just looking for suggestions on what to check when I am next on board.

 

The engine starts instantly (with or without heaters) usually with less than a second of cranking and runs smoothly

 

with the throttle set for running at 1300 rpm it will hunt between 1250 and 1350 rpm taking about 2 seconds to go between upper an lower speeds. (when knocked up or down a touch it will sit at 1320 or 1280 all day)

 

at all other throttle settings it is rock solid from 950 rpm through to 2000 rpm (although it has never spent much time above 1800)

 

there is no play in the throttle linkage and nothing visibly moving when it's hunting.

 

engine is a lister lpws4 with about 3000 hours on it.

[OldGoat]

Charging depleted batteries??

[Jess--]

Charging depleted batteries??

can rule out batteries, it will do the same at the start of the day as the end of a day cruising.

 

also have solar on the boat so the batteries are always in pretty good shape

[Tony Dunkley]

I'm not on the boat at the moment so am just looking for suggestions on what to check when I am next on board.

 

The engine starts instantly (with or without heaters) usually with less than a second of cranking and runs smoothly

 

with the throttle set for running at 1300 rpm it will hunt between 1250 and 1350 rpm taking about 2 seconds to go between upper an lower speeds. (when knocked up or down a touch it will sit at 1320 or 1280 all day)

 

at all other throttle settings it is rock solid from 950 rpm through to 2000 rpm (although it has never spent much time above 1800)

 

there is no play in the throttle linkage and nothing visibly moving when it's hunting.

 

engine is a lister lpws4 with about 3000 hours on it.

 

It's wear or mal-adjustment, or a combination of both in the governor and linkage, . . . . not uncommon in multi cylinder Listers of any size or vintage with single element injector pumps.

I've got a 150 bhp x 6 cylinder Lister JW6 in a tug that has hunted when idling or at low revs on load since it was new in the early 1980's.

[nicknorman]

Low frequency hunting like that is caused by too much sticktion in the fuel bar compared to the governor springs strength. On some engine like our Beta 43 you can adjust the spring preload to get rid of any hunting but I've no idea if there is such an adjustment on an LPWS4. What I can say is the the boat we borrowed for many years had an LPWS4 and it didn't hunt, so it is not a fundamental design fault.

[OldGoat]

nicknorman, on 25 Jul 2016 - 5:00 PM, said:

Low frequency hunting like that is caused by too much sticktion in the fuel bar compared to the governor springs strength. On some engine like our Beta 43 you can adjust the spring preload to get rid of any hunting but I've no idea if there is such an adjustment on an LPWS4. What I can say is the the boat we borrowed for many years had an LPWS4 and it didn't hunt, so it is not a fundamental design fault.

Now that makes a lot of sense. On my Betas the spring was quite light and more appropriately "just hooked into a hole" - so it could be easily dislodged - or even fall off, there are lot of bits at that end of the engine....

[granddad]

Thank you for both the question posed and the reply.

My lister petter of 1999 (LPW4) has been rebuilt recently and I have your problem but with no idea of the cause. After an hour running the mid range engine speed varies by +/- 50 hertz cycling at 2 second intervals.

Its unlikely that the governor was disturbed in the rebuild but the fuel pumps are new and the lube oil is the thinner running in oil.

I was about to search for a fuel line letting in air but your explanation means that I no longer need to worry. The engine is not about to stop.

Thank you for setting my mind at rest as I have a long journey this weekend to get the bottom blacked in cropredy. I prefer a worry free journey

Ken