Perkins 4.108 erratic rpm's

[Dirk Williams]

Fantastic, input. I'm writing this all down in my trouble shooting problem/ solutions, book.

DW

[donradcliffe]

When my 4108 rpm started to wander, it was an early warning sign to change the fuel filter before things got worse.

[Old Swampy]

The only rpm abnormal behavior we had with our 4-108 was slowing down due to filter clogging. We didn't have a polisher then, but each spring I would pump out the sludge from the tank. After settling, the more or less clear fuel went to my home fuel tank. Of course it, too, has filters that need to be changed periodically.

[BobLoucks]

I have same engine had same problem. In my case the problem was solved by cleaning the sediment filter, water separator and fuel filter housings and replacing all filters. Then I tightened all fittings in the fuel system. Problem solved.

Now this boat is new to me and the fuel system looked like it hadn't been serviced in years. But same problem fixed by servicing the fuel supply system.

Good luck, I will be interested in how you solve this.

[michaelratinter]

I had that problem with my 4.236 at 1800 rpm. I changed the fuel filter and it ran fine for 25 more hours. Then the lift pump failed. I replaced the lift pump and replaced the ancient Fram filters with a Racor filter. No problems since.

[Basil]

I ran a 4-108 for a number of years an it was the best motor I have had, air leak or blocked filter would be my guess if the filter becomes blocked then it creates a situation where the air starts to be sucked into the filter.When you get the problem sorted have a think about installing a inline pump as near as possible to your fuel tank as possible, this then insures that you are pumping your fuel to the motor not pulling it to the motor.


This was recommended by the USA agent for Beta marine, an is catching on fast, I have installed this on my yacht at a cost of around $50 NZ putting one pump on each tank an a switch on the panel.
I never have any trouble with filter changes or air leaks as the fuel is pumped not draw up into the motor.
Regards
Phil

[thebootlegger]

I am watching this threat as we have experienced this in our 4.108 also. ..THANKS guys. ...

[Triumphant]

Originally Posted by michaelratinter

I had that problem with my 4.236 at 1800 rpm. I changed the fuel filter and it ran fine for 25 more hours. Then the lift pump failed. I replaced the lift pump and replaced the ancient Fram filters with a Racor filter. No problems since.

I had exactly the same problem on my 4236M but at 1500 RPM, replacing the 28 year old lift pump sorted it

[Dirk Williams]

Question, new guy, what is a " polisher" and what is the brand name of the pump at the fuel tank?

Thank you, in advance.

Dirk

[Tobaccoblender]

Wow! Great replies, and thank you everybody.
Up until now I have been a bit quiet, but only because I stopped receiving notifications of new posts..
Anyway, I have found the cause and solved it.
The first thing I noticed was the fuel line from the primary filter to the lift pump was beginning to look old and a bit perished so I replaced that.
Then I noticed the line from the tank pickup to the primary was new but when I slackened the hose clamp, it just fell of the primary filter spigot. It was one size too big, ie 10mm id instead of 8mm. It might have been working ok, but if that hose clamp worked even a tiny bit loose, air would have been sucked in for sure.
Then I arrived at the fuel tank....at first I couldn't remove the pickup pipe to check the filter because half the galley cupboards had been built over the exact spot where you withdraw the pickup. After 20 mins with a hole saw and my trusty Makita I was able to unscrew it.
At the top end, where the flexible fuel line attaches to a spigot, is a 90 deg fitting, out of which comes the alloy pickup tube.
There was no visible screen filter anywhere but if I shined a light down the tube or through the 90deg fitting on the other end I could not see the light exiting anywhere. Then I realised the alloy tube screwed into the 90 fitting so precisely there were no residual threads showing- ie it looked as if it were pressed in.
When I unscrewed it, there she was, slid down into the pickup pipe, held in place with a tiny flange at the top, a brass screen THAT WAS COMPLETELY MUNGED UP WITH A BLACK STICKY TARRY GOOP. More or less sealed up!
Cleaned all that off, new filters and we've been motoring today for 4 hours and not so much as a hiccup.
Excellent result and again, I appreciate everybody's input.
Cheers
Paddy
Gulfstar H45 sloop.

[HappyMdRSailor]

Congrats!!!

Thanks for the resolution post Paddy!

[Cheechako]

Great find Paddy! As you noted, rubber hose is often an issue. I’m not a big fan of flexible rubber tubing/hose in the fuel system myself. Except where absolutely necessary. As you noted, when you took the clamp off, the tube was very loose on the fitting. I have had this issue a few times. I’ve also found with a clamp as tight as you can get it before stripping it, you can often still spin the hose on the barb fitting. It seems rare to get a barb and hose that fit tight. Once I made the mistake of using USCG approved hose, The damn stuff was about ¾-7/8” OD.....huge. It was only 5/16 ID. It was the worst for spinning and being loose on the fittings. I far prefer copper tube wherever possible.

[DeepFrz]

Wow, a hidden screen on the pickup. That was a nasty thing for the builder to do. Glad you found it.

What type of boat do you have? If its a modern build then other owners should be aware of the potential blockage.

[Tobaccoblender]

No, it's not a modern build, she's a 1985 Gulfstar H45, made in Florida but deivered here in Europe from brand new.
But in this case, although the filter screen was ingeniously well hidden, I would hage found it in the end just because you KNOW there has to be a gauze filter somewhere between the diesel fuel itself and the primary filter...just a case of searching and never giving up!
That aside, we have now put about 150hrs on the motor since resolving the dirty filter mesh issue and she is running as smooth as silk.
As I write this we are motoring (no wind today!) down through the southern Ionian sea, alongside the Peleponnese in Greece, heading to Crete. It is now 13.15 Greek time and I calculate an eta Crete of about 06.30 tomorrow morning. Beautiful sunny day, the Med is a sparkling deep blue and my Perkins 4.108 is humming along like a Rolls Royce RB211!
Life is good.
Btw, anybody know why I don't receive notifications of a reply even though in the 'Thread subscription' box below it shows 'Instant email notification'?

[Tobaccoblender]

Originally Posted by Dirk Williams

Question, new guy, what is a " polisher" and what is the brand name of the pump at the fuel tank?

Thank you, in advance.

Dirk

Dirk, a fuel polisher is a cool funnel filter through which you pour the fuel into your tank and at strips all the grit and general crap out of the fuel- I believe they even remove any water.
Can't help re brand of pump but I would have thought any decent auto supply place would be able to suggest a suitable pump. It is not high pressure or high volume- just has to suck the fuel out of the tank and get as fsr as the injector pump. Good idea though as it means that first hose, from the tank to the primary filter and then the hose from the primary filter to the mechanical lift pump will be under slight pressure instead of under vacuum. This means a leak in either those hoses will result in fuel leaking out of the hose instead of air being sucked in. The differrnce of course being with the pressurized line leaking a bit the engine won't conk out on you!
Best of luck with you HR 33!