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Discussion Starter · #1 ·
Although not directly related to a motorhome, it could be.

I have an old sit on mower that is powered by a Kubota 4 cyl diesel engine (around 1992 I think) it has no fancy ECU or anything.

The engine starts fine from cold and runs normally for about 5-10 mins, then it looses power and goes through a cycle of the revs slowing down for about 15 secs, then speeding up for about the same time, this repeats over and over again, but it will not go back to full power.

Has anyone got any ideas? I've changed the fuel filters, but this doesn't seem to make any difference.

It's the starting up and running normally from cold initially that is really puzzling me.

Any help gratefully received
 

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Not very helpful but this is similar to what happened to my V6 Granada years ago. The fault turned out to be a leak at the inlet manifold which was drawing air in, it started to stall and the anti stall mechanism came into play and it continued to cycle as you describe.
The fault was found by spraying WD40 at it which sealed the leak for a short time allowing it to run normally for a while.
 

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Change the other fuel filter in the tank, situated immediately above the outlet pipe. I had a similar problem with an old Petter diesel engine which hunted on load as the fuel filter was almost totally blocked.

If it were air in the fuel starting would be a problem

Have you tried disconnecting the feed pipe at the injector pump to confirm a good fuel flow?


c.
 

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Discussion Starter · #5 ·
There's a filter in the tank?

I presume I get at it by removing the fuel gauge sender unit. Would that be correct?

The fuel seems to be flowing OK, but I've no idea what the rate should be.

I noticed that the fuel returned to the tank seems to increase as the revs drop, which seems logical .

Thanks for the suggestions


Andrew
 

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On my old Petter the top of the fitting for the outlet pipe had a small fine tubular mesh filter. this was caked with crud and dead flies etc. I removed this and fitted a bigger external filter.

Do the quick test by disconnecting the pipe at the injector pump to see if fuel flows well.. If it does then forget filters and we can think again.
 

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Hi,
Another possible cause could be a blocked tank breather, easily checked by leaving the fuel filler off, if its not that, is the injector pump fed from a lift pump? there is a filter built into that get attable? by undoing the ring of screws and lifting the top off, if there is not a problem with fuel getting to the injector pump then you are looking at governor problems. Last thing I can think of is water in the diesel? It must be some mower with a 4 pot Kubota in it,
Regards,
Chris
and good night. :)
 

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Discussion Starter · #8 ·
There is a possibility that some water got into the fuel, but I'm pretty sure that got sorted, and the fuel supply to the pump seems adequate. I'll try and measure it today.

The thing that baffles me is why it runs fine when cold from start up and then develops this problem when it's warmed up.

What happens to the fueling of a non ECU diesel engine when it warms up?

Andrew
 

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Hi,
If I remember correctly the Kubota is fitted with an in line injector pump with four pump pistons connected by an internal rack. There is a cold start position which allows excess fuel to be injected to facilitate easier cold starting but this only operates when starting. The actual engine speed is controlled by the rack and the position of this is controlled by a mechanical governor. If any of the components have become stiff which is possibly what happens when the engine warms up it will give the symptoms you decribe. The engine is stopped by pushing the rack over to a position where no fuel is delivered the more recent engines having a solenoid to do this. Stripping the fuel injector pump is a specialist job as is refitting it afterwards, if you are sure that plenty of clean fuel is getting to the injector pump I think you need to contact a Kubota dealer,
Regards,
Chris.
 

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Discussion Starter · #10 ·
Hi Chris,

Thanks for the info, I fear you may be correct.

As you seem to know about these things, would it be possible for an engineer to remove the pump at my premises, take it away to recondition it, and return to fit it.

I ask this, as the mower would obviously have to be trailered, if it cannot be done the way I suggested.

Andrew
 

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Shame,
I sold via Ebay my 40 year old ride on 18 months back. It cost me £100 in tyres as I was given it as a scrapper by a hacked off farmer. After many hours of loving restoration I eventually learnt why the farmer was hacked off!

Back to walking behind the Hayter again.

c.
 

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Discussion Starter · #12 ·
Hi Clive,

Mine's a Ransomes 225, which is pretty knackered, but I need something like it as I've got about 3 acres to cut.

The decision is whether I spend more money on it or get something else.


Andrew
 

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Kubota diesel

One additional comment- how old is the diesel in your tank? I've heard recently that diesel containing bio fuel (as they do today even a small percentage) goes off quite quickly in say a winter's storage period. It might run ok in excess fuel when you cold start but not in normal fuel rate.
Otherwise sounds like you have pump/governor trouble as per Sticky's comments.
 

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Discussion Starter · #14 ·
Thanks for the info Excavator. I think possibly you may be on to something, and this would certainly tie in with the fact that it runs OK in cold start mode.

Before I do anything else, I'll drain the tank and get some fresh diesel and see if this makes any difference.

Thanks



Andrew
 

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Hi again,
The excess fuel device (cold start) only operates during start up from stationary, not all engines will use it, some have an electric heater plug or hot fuel dropper its difficult to say without seeing it. If I was in your position I would get an agent to look at it and get his advice, removing the injector pump and refitting it is simple enough when you know how, they may suggest a service exchange pump, you have to decide if its better to repair or replace the mower,
regards,
Chris.
 
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