Bleeding air in fuel!

Porthandbuoy

Porthandbuoy

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Is there an easy way of locating a tiny tiny leak in the suction side of my lift pump?
My 1GM10 will run happily for 39 - 40 minutes before spluttering to a halt. Bleed the system and away she goes again; quite happy.
I've put a priming bulb between dip tube and filter. Every 15 minutes or so I dive below, squeeze the bulb a few times until it goes 'hard', and the engine will run forever. (I thought the bulb might be the problem. It isn't, but it is a temporary fix).
Wherever the air is getting in it must be the tiniest of holes as even by squeezing the bulb really hard I cannot find a fuel weep.

Any ideas? :confused:
 
No easy way I know of, you'll just have to take it any joins apart, inspect them and put them back together

My guess is it will be somewhere near the primary fuel filter, may be a distorted copper washer around the bleed bolt or summut like that
 
The only way is to divide the system into sections and apply suction to each part of it.
If you have a Pela type oil extractor, use that to suck fuel through and check for air.
If you block one end of a tube then apply vacuum using a syringe, you may see little air bubbles forming.
It's worth checking that it is just an air leak, not a near blockage that means the lift pump is having to create loads of suction to shift the fuel.
You could try feeding the lift pump from a can of clean diesel, bypassing the pre-filter etc.
That should eliminate the lift pump.
If you can insert one of those clear plastic filters at some point in the system, that will collect any passing air, telling you if the leak is upstream or down. I would think twice about leaving one of those in the system, as the can be fragile and a fire risk.

Renewing any flexible hoses is probably worthwhile.
 
lw395 said:
The only way is to divide the system into sections and apply suction to each part of it.
If you have a Pela type oil extractor, use that to suck fuel through and check for air.
If you block one end of a tube then apply vacuum using a syringe, you may see little air bubbles forming.
It's worth checking that it is just an air leak, not a near blockage that means the lift pump is having to create loads of suction to shift the fuel.
You could try feeding the lift pump from a can of clean diesel, bypassing the pre-filter etc.
That should eliminate the lift pump.
If you can insert one of those clear plastic filters at some point in the system, that will collect any passing air, telling you if the leak is upstream or down. I would think twice about leaving one of those in the system, as the can be fragile and a fire risk.

Renewing any flexible hoses is probably worthwhile.
Click to expand...

Some good suggestions there. Thank you.

Most of the hoses are all new. Only the one between primary filter and lift pump is 'old'. Lift pump is new.
I like the idea of using a temporary filter and using it to bypass the primary. I'll try that.
 
I would disconnect the line at the tank, block it off and then connect the priming bulb to the pipe feeding the lift pump so you can pressurise the line between the tank outlet and the lift pump inlet. You can then look to air or fuel leaking from the connections in the line.
 
It can be quite difficult to detect the presence of fuel at a tiny leak. Just looking at it you will miss it. The simple way is to get some coloured soft tissue (Tesco's valu-pak loo roll in a pleasing pink does quite nicely!). Wipe every joint absolutely clean, then pressurise it with the bulb, or run the engine fro half an hour. Now using a clean bit of tissue, carefully wipe each joint again: any trace of diesel will darken the tissue.

the other way is to clean everything thoroughly, then use talc powder at each joint. Makes the engine room smell nice too! The key with either way is starting off with it 100% clean and dry.
 
what make/model primary filter?

Porthandbuoy said:
Yep. Twice at least. New copper washers and everything...
Click to expand...

I have never found a sure fire way to spot where an air leak is coming from (not quite true - see below) but I had a very similar issue with my generator, and was equally puzzled for a while. However I did find it courtesy of advice form this forum. I have a CAV primary filter, and there is a small 'O' ring around the central bolt which is not that obvious and was not supplied with the new filter. I hadn't spotted it and neither had the yard, who hadn't changed it in 5 years despite doing a full service every winter. Replacing this O-ring fixed the problem. It's possible that an O-ring seal would act as a one-way valve letting in air but sealing against positive pressure, so it never let out any diesel and hence the leak was impossible to spot.

So if you've a CAV (with Lucas/Delco/Delphi HDF296 or equivalent element) could it be this?

Digression on a sure fire way to trace air leaks into a vacuum: while an undergraduate I spent a fun summer helping in a very minor way to build the Oxford 'folded-tandem' particle accelerator. Naturally we needed very high vacuum - 10^-10 torr - and so chasing tiny leaks became an obsession. The way we did it was to put a mass-spectrometer into the vacuum chamber, set it to detect mass/charge ratio of 3, and go round every mm of joint with a small 'aerosol' canister containing Helium 3. As soon as the detector registered any current, bingo! I could pinpoint tiny leaks to about 2mm like this. Might be cheaper to buy a new yacht 'tho...
 
The leak might be inside the lifty pump. A pin hole in the diaphram? Or just gunk in the lift pump filter? Perhaps the lift pumpn cap is not tight or the O ring or gasket perished?

Just being 'new' doesn't mean it hasn't been sitting on a shelf for ages?
 
Had a similar problem when I first bought Mojo. Engine just "serviced" by marine engineer, but only ran for around twenty minutes a time and needed bleeding to get it going again. It turned out that the compressed ends of the rubber hoses had softened to a gummy consistency. With the old ends cut off the joints were fine again and the engine would start after standing for weeks and run continuously.

Rob.
 
I've had a similar problem with a 1GM10 for a couple of years. In the end, I've changed both fuel filters (including a completely new housing and set of connectors for the filter by the tank) and new hoses. Hopefully now fixed. One definite problem I had was that the fuel filter on the engine was gummed up with diesel slime, which I'm sure made matters worse - could well have been the cause as it meant more suction for the lift pump (I think). I've put it down to using ordinary white diesel from a petrol station - seems to breed diesel bug very easily.
 
get a u tube manometer from a plumbers merchant. use your bulb to give you the suction needed. dont ignore the bit of pipe in the tank! nor ignore the new pump diaphram or its lid, if removeable.

suction leaks are the bugger to find.
 
I had a very similar problem with a 1gm10. It turned out to be the engine fuel filter - tightening the knurled ring didn't manage to pull the filter bowl up into the O-ring sufficiently tightly. I bought some fatter O-rings and the problem was cured instantly. I only found the problem after stripping and re-assembling the rest of the fuel system, and installing a temporary 'day tank' above the engine. This was on a brand new installation.

Try www.simplybearings.co.uk for small quantities of O-rings.
 
I think that your problem is not a leak allowing diesel to leak out but air entering through a leak allowing fuel to run back into the tank! This happens particularly where the pipe runs are higher than the pipe into the tank. Absolute bu**er to find! A non-return valve helps.
 
Juggler7823 said:
I think that your problem is not a leak allowing diesel to leak out but air entering through a leak allowing fuel to run back into the tank! This happens particularly where the pipe runs are higher than the pipe into the tank. Absolute bu**er to find! A non-return valve helps.
Click to expand...

I don't have diesel leaking out. I definitely have air getting in and it has to be on the suction side of the lift pump (or as one poster suggested, the pump itself).
The priming bulb has two check valves; one on the inlet, one on the outlet. When I crack a union nothing drains back to the tank.

My problem is most likely the CAV filter housing with it's myriad of seals (2 inlet ports, 2 outlet ports, a bleed screw, the bolt that holds the assembly together, the 'O' rings above and below the filter cartridge, the 'O' ring below the clear bowl, and finally the drain connection) What a carp design for a negative pressure system!

Think I'll fit a Racor.
 
If your tank is sound you could pressurise the tank via the breather pipe, you will only need a low pressure.
I have found that shaving foam on the possible subjects normaly works as this will vanish when exposed to fuel vapour.
Another tip is to fit a peice of clear pipe on the fuel return line as a temporary indicator of how much air (and fuel) is going through the system.
 
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