Fuel system problem, with photo, advice needed!!

[Feneris]

I've got what's hopefully a simple problem with the fuel system. I think the fuel is syphoning back down into the tank. The tank is lowest, the fuel filter on the right is higher, and the carbs are highest. If I leave the boat for along period (months), the fuel line from the filter to the engine contains only air. The fuel pump is on the side of the engine, it has a manual primer on it, but it doesn't seem to do anything. Cranking the engine doesn't help either. I suspect the fuel pump isn't willing to self prime when the line is full of air. It pumps fine when the line is full of fuel. Previously I used a syringe to fill the line with petrol.

Options are, fit a primer bulb in the rubber pipe from the fuel filter to the fuel pump. This is cheapest and easiest.

Or I could buy a Delphi fuel filter, which as a manual primer on it, see link below:

http://www.thornycroftparts.co.uk/C...HAND_PRIMER_-_GLASS_BOWL/p207754_3527633.aspx

I could also fit a non-return valve to the fuel line. On my current fuel filter, I can't turn the bleed screw at the bottom, it's seized and will probably snap off. So there's an advantage to buying a new Delphi. Avoiding a rubber primer means I could also replace the rubber line, from the filter to the engine, with a metal one for fire safety..

Or have I missed something, should I be able to make what I've already got work??

 

[volvopaul]

Hi, I sometimes fit the hand primer pump but I don't think it's suitable for petrol use.

I'd say your lift pump either has a split diaphragm or one of the valves has debris it it holding it off it's seat.

 

[LittleShip]

Hi, I sometimes fit the hand primer pump but I don't think it's suitable for petrol use.

I'd say your lift pump either has a split diaphragm or one of the valves has debris it it holding it off it's seat.I assume Paul is talking about the small one way valves in the lift pump

You could concider fitting a small electric pump if all else fails, but I would go with Pauls answer and renew the pump and fuel lines first.

Tom

 

[Feneris]

Thankyou for the above replies;

I opened the pump to check the diaphram, it looked ok. At £75 for a new one, I'm not replacing it just-in-case!! I have now found a complete new pump for £112 new (Coastal rides).

I will check the valve seats, if I can get to them. Could it be that this pump is just very inefficient with air, and it's got a long line of air to clear while lifting the fuel behind the air???

I guess normally a fuel pump should be able to deal with air??

 

[LittleShip]

I would have thought that you could buy a refurbisment kit for the fuel pump.

It does sound like air getting in. The little valves in the fuel pump are set up so that they wont allow fuel to pass backwards down the line, if they are in good condition you must have a leak on the fuel line/filter somewhere.

It would be good practice to renew those fuel lines and clip them. Look very closely at the aluminium washers on the top of the filter, joints, unions and any other connections, it is possible that it will let air into the system but not show any signs of fluid loss.

Tom

 

[moonraker 36]

why not turn off the fuel tap when not in use. to stop the petrol syphoning back into tank?
but like every said must have an air leak some were.

 

[burgundyben]

If the engine stops in such a position that the cam that operates the lift pump is in the fully lifted position then the manual lever on the lift pump will not have any affect.

Half a turn on the crank with solve that and the manual lift lever will operate.

 

[Feneris]

Thanks for all the replies. I removed the top of the fuel pump, and found that I could blow down the fuel line, the wrong way. There must have been some debris in the valve, after a bit of fiddling with it, problem solved and the pump's valve provide the one-way valve on the fuel line. Now the manual primer lever works as well.

I removed one of the banjo bolts, to the first carb, and had to replace the crush washer. I couldn't get crush washers locally so got some off ebay. I don't know if they're overly hard washers, but I had to do the banjo bolt up really tightly to stop any leak. The faces of the carb, fuel connector and bolt were all perfectly clean and free from damage.

The other washers were identical, not sure if it needs to be uber tight, or if the washers aren't the best?? Obviously I was very wary of striping the thread in the carb!!!

 

[kashurst]

they shouldn't need to be overly tight, if you are worried try dressing the faces of the carb and banjo etc with a fine file to take off any corrosion. Were the new washers copper or some other material?

 

[pappaecho]

had the same problem ona yacht 15 years ago. Fitted a "rubber bulb pump" in the petrol line. It reprimed the system in 30 seconds.

I dont know exactly the name of the unit, but chandlers stock them, and I think they also have a non return valve. They are fitted to big outboards, which have an external fuel tank.. on a rib for example