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Air in the machine!!


Peri Pigott

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Hi all - is there anyone out there that has a 2 cylinder Ruston Hornsby Engine? 

We seem to be having a lot of trouble with air in the system. I have completely overhauled the twin fuel filters, new seals, washers, filters etc.......bled ever bleed screw I can find. 

Undid to large nuts on the injectors - lots of air came out....... have run it in gear for over 2 hours now trying to push through and whilst it hasn’t completely died!! The revs dip quite a bit...... I have it running now, half hour into another hour,  and it’s running, sounds sweet but revs keep dropping! It’s starts up ok too........

......we have been towed in twice in the last 2 weeks- getting embarrassing now ??. Can anyone offer some other advice!! Thanks 

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Is the level in your fuel tank low ?

It could be 'sloshing' and letting the pipe come out of the fuel and sucking air intermittently (The pipe does not go to the bottom of the tank - normally stops several inches above bottom)

Have you checked all joints / unions for tightness ?

Wrap a little toilet roll / kitchen roll around every joint and see if it leaks (although air seems to get in where fuel doesn't get out)

 

Could the new fuel filter be partially blocked having sucked up a load of crud ?

Allows some fuel thru' but then not enough to keep running properly and 'splutters', rest with pump running and it will 'fill up' & start again.

Edited by Alan de Enfield
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Hi Alan thanks so much for your quick reply.

 

all as mentioned I have done. Tank is 3/4 full. All joints and unions were checked and re-checked the filter is only 2 weeks old but have today put in a brand new filter...... just incase......all seals/washers etc are new in today too, all sitting pretty! 

Thing is there is not one ‘splutter’, engine sounds wonderful until it starts to ‘die’ but she does pick up the revs again...... I’m going to try the fuel pump tomorrow, could be that needs a ‘bleed’ it’s just a pig to get to! 

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14 minutes ago, Peri Pigott said:

Thing is there is not one ‘splutter’, engine sounds wonderful until it starts to ‘die’ but she does pick up the revs again

That certainly sounds like fuel starvation - as if it is using the fuel in 'the system' faster than it can be replenished, it runs 'sweetly' whilst fuel is available, but as fuel becomes 'short' it splutters (maybe running on only one cylinder ?) then as the fuel usage is reduced, the pump can catch up again, fills the pipes and away it goes again, repeat...…………………… repeat.

 

There could well be another filter built into, or very close to the pump. I don't know that specific engine but some older engines have a fine mesh filter built into the pump / pump inlet.

Just things to look for.

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12 hours ago, mark99 said:

Lift pump. 

My thought too. 

Perhaps a perforated or leaking diaphragm.

You could temporarily rig up a gravity feed so the whole fuel system is under positive pressure. If it then runs OK that confirms there is air getting in somewere on the suction side.

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I had similar some years back and eventually found a leak on the flexi into the lift pump. When it sucks in air, there is no damp tell tale to guide you. My leak was where the rubber was swaged onto the nipple. The rubber was split under the clamp.

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6 hours ago, Alan de Enfield said:

Just a sea-capable "Tupperware" (but it does have a 2600 litre fuel tank giving it a range of 2000+ miles)

 

Sounds fab! 

So today I managed to get to the fuel pump (twin) and through the nylon fuel pipe I can see lots of air bubbling away so was really chuffed, did more running of the engine to push fuel and air thru’ and still can’t get it shifted! It works for a bit then air is being drawn in from somewhere, so I’m afraid I’ve given up and will have to call in the Profs! hey ho........ all the best to you .

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