Bleeding diesel line

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eddystone

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I always have problems with this but often manage it through random actions and I can't remember what I did on the previous attempt. Managed to get the bowl on the CAV Primary to fill after about x00 operations of the lift pump but whatever I do can't get any fuel to come out of bleed nut on said CAV. Should I have both bleed nuts, primary and secondary open or have secondary closed whilst working the primary?
 
You are using the lift pump to pull the air out of the primary filter ... right ? ... it may not pump air all that efficiently!
The filter bleed screws are closed .... right ? .. or you'll suck air in.

Do you have a bleed screw down stream of the pump open for the air to vent ? or are you attempting to shove it through th secondary filter and back to the tank via the spill back line ?

Is the filter below the level of the fuel in the tank? Once primed fuel should flow out of the filter bleed screws but it wont it they are above the fuel level in the tank and if you operate the lift pump with them open you'll suck in air.

Maybe the geometry of your fuel system would make a squeezy bulb between tank and filter a good idea
 
If your CAV bowl, horrid things, is beneath the level of the fuel tank if should fill by gravity, once you have 'flow' that might need some suction to start. Once things are going then open the bleed valve at the primary filter until fluid seeps out, then move the the secondary filter (always good to fill this with clean fuel) and pump until fluid seeps out. I've usually been lucky and not needed to 'crack the injectors' but if you do more pumping is required.
 
eddystone said:
I always have problems with this but often manage it through random actions and I can't remember what I did on the previous attempt. Managed to get the bowl on the CAV Primary to fill after about x00 operations of the lift pump but whatever I do can't get any fuel to come out of bleed nut on said CAV. Should I have both bleed nuts, primary and secondary open or have secondary closed whilst working the primary?
Click to expand...
What engine?
 
VicS said:
You are using the lift pump to pull the air out of the primary filter ... right ? ... it may not pump air all that efficiently!
The filter bleed screws are closed .... right ? .. or you'll suck air in.

Do you have a bleed screw down stream of the pump open for the air to vent ? or are you attempting to shove it through th secondary filter and back to the tank via the spill back line ?

Is the filter below the level of the fuel in the tank? Once primed fuel should flow out of the filter bleed screws but it wont it they are above the fuel level in the tank and if you operate the lift pump with them open you'll suck in air.

Maybe the geometry of your fuel system would make a squeezy bulb between tank and filter a good idea
Click to expand...

Vic is exactly right here. If the bowl of the primary filter isn't filling and it IS below tank level, it's likely that there's a blockage. Mine was always caused by the diesel bug black jelly covering the pipe, blocking the filter in the tank. The lift pump on my engines has always been a mechanical cam operated pump and if the cam is pointing at the lever, you'll not get a good stroke and bleeding up to the fine filter will be a tedious operation. Once you have fuel at the fine filter bleed point you can move on to the injector pump. using the lift pump again. After this I run the starter to turn the engine with the decompressor on to get fuel to the injector. This lightens the load on the starter motor. Dropping the decompressor after a minute or so usually starts the engine. If you have a multi cylinder engine, you'll need to decompress each cylinder. The injectors bleed excess fuel back into the tank and this takes out any residual bubbles. I have never needed a squeeze bulb between mt tank and the primary filter, but I know many who have one and they tell me it speeds things up, especially if you have a long fuel line.
 
Laysula said:
Chuck the CAV away and fit a Racor 500 copy and a squeezy bulb between the tank and filter.
Click to expand...
You may want to ask Racor about this...... I did for a fifty hp engine, and they advised their product which looks and works very much the same as the CAV unit......!
Racor's tech advice is excellent by the way!
 
Nothing wrong with CAV filters, the problem lies with users.

The filter type has absolutely nothing to do with the OP's problem.
 
My fuel lines aren't fire resistant - nor are my tanks, so that bulb going up would be the least of my worries.

As for leaks, yes, they would be a pain, but at change for a tenner, it wouldn't hurt to carry a spare. One of the things I have to look at on Jazzcat is the fuel supply. The filters are big beasts and above the fuel level, so I'm wondering about fitting these. I really don't know how I'd bleed the system as it stands.
 
I have found that brimming the fuel tank and filler neck ensures a head of fuel will force any trapped air to bleed points on primary and secondary filters without need to use the lift pump.
A few tickles on the lift pump and you will hear any remaining air in the injector engine pipe work bubble into the tank and usual exit the vent.
Simple trick lets gravity do the work for you if you don't have a bulb fitted.

I have considered fitting a bulb but access to my tank feed line or primary filter is not exactly easy so I just prefer to pour a bit of red out of the spare 10litre Jerry can.

It also tests if you have any pick up blockage in your tank.
 
OK so what have I done wrong!?
Have come back to boat for another go. Closed both bleed nuts and did some pumping; turned the engine over from flywheel nut but makes no difference to movement on lever (it’s a Beta30) open up primary nut and pump- no fuel coming out; close primary and open secondary and pump again - some fuel but can’t make bubbly disappear
Try engine and it starts quite easily and idles continuously; put it under load at about 1500 and still runs; I have to try under greater load to purge any air out of the cooling system but so far so good
But this shouldn’t be happening - have I forced air into the recesses of the injection pump which will subsequently explode and destroy the engine?
 
BTW I haven’t properly checked the relative levels of CAV and fuel tank but last time I did this the bowl filled under gravity when fuel turned on (so considerate of Sadler to put the fuel shut off valve underneath the tank) this time it needed a bit of assistance from the lift pump
 
eddystone said:
OK so what have I done wrong!?
Have come back to boat for another go. Closed both bleed nuts and did some pumping; turned the engine over from flywheel nut but makes no difference to movement on lever (it’s a Beta30) open up primary nut and pump- no fuel coming out; close primary and open secondary and pump again - some fuel but can’t make bubbly disappear
Try engine and it starts quite easily and idles continuously; put it under load at about 1500 and still runs; I have to try under greater load to purge any air out of the cooling system but so far so good
But this shouldn’t be happening - have I forced air into the recesses of the injection pump which will subsequently explode and destroy the engine?
Click to expand...
Every time you open the bleed screw/nut on the primary filter, which I assume is before the lift pump, you will be sucking air in. So, when you open the bleed screw on the secondary filter, which I assume is after the lift pump, you will then release some of that air. You must only open bleed screws that are after the lift pump. What engine do you have?

Www.solocoastalsailing.co.uk
 
eddystone said:
OK so what have I done wrong!?
Have come back to boat for another go. Closed both bleed nuts and did some pumping; turned the engine over from flywheel nut but makes no difference to movement on lever (it’s a Beta30) open up primary nut and pump- no fuel coming out; close primary and open secondary and pump again - some fuel but can’t make bubbly disappear
Try engine and it starts quite easily and idles continuously; put it under load at about 1500 and still runs; I have to try under greater load to purge any air out of the cooling system but so far so good
But this shouldn’t be happening - have I forced air into the recesses of the injection pump which will subsequently explode and destroy the engine?
Click to expand...
We have a Beta 50 and can’t say I’ve ever managed to get the manual lift pump priming lever to do anything (apart from generate a few laughs at whoever is frantically jiggling away!)… maybe it’s just me/us?!

So instead I just get as much air out as possible (fill our racor copy with diesel) and then crank away (taking breaks every 10 seconds as required). May not be pretty, but after a few tries it catches and starts to ‘self bleed’.

No danger to the pump/engine, AFAIK, so long as you don’t stress the starter too much.

I plan to fit an electric lift pump long term, but will try the priming bulb thing for now.

Pumps on top of filter housings can also leak. I had particular trouble diagnosing rough running on a Jap pickup fitted with a Denso style pump/primer filter housing (the membrane inside had deteriorated letting air in - but think there it is a non-return setup so no tell-tale fuel leak to give it away). No option is perfect or future-leak-proof.
 
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