Time for an addition to this section of the forum I think.
After a little backgroung reading it occurs to me that the position of the fuel filter is incorrect in our Interceptors. At the moment the filter on my car is located between the tank and the fuel pump; between the pump and carb is the fuel vapour seperator. As far as I can tell this vapour seperator also functions as a fuel filter therefore making the other filter unnecessary? (see page 14-78 in the 1975 440 workshop manual - Robey reprint) There is also a small cylindrical plastic filter on the end of the fuel pick-up pipe in the fuel tank.
It has come to my attention that if the car is not used for many weeks it takes an age of churning to get fuel up to the carb. I wonder if this is due to the pump having to draw fuel through a completely dry fuel line and empty filter?
I'm thinking of removing the fuel filter and relying on the vapour sep/filter combo only, gentlemen any thoughts?
Fuel vapour seperator
The filters are positioned to keep the dirt in certain places. The nylon filter on the pickup is there to filter particles up to a certain size and keep them in the fuel tank. The main fuel filter keeps the smaller particles from entering the fuel line and the pump, the vapour seperator is to allow a return flow to the tank and provide a final filtering after the pump. It's not an optimal system though.
If you look at the cutaway view Fig.6 of the vapour seperator, it's not a very good filter as it has an outlet from the filtered side back to the tank through the orifice which is shown unfiltered.
The fuel filter is also prior to the pump on the Interceptor and would be better fitted after the vapour seperator. As most of these filters are of the paper element type, they give a restriction to flow as a pre-filter, moreso as they become blocked, they work better under pressure. Let's discuss this further, I think it will be interesting!
Mike
If you look at the cutaway view Fig.6 of the vapour seperator, it's not a very good filter as it has an outlet from the filtered side back to the tank through the orifice which is shown unfiltered.
The fuel filter is also prior to the pump on the Interceptor and would be better fitted after the vapour seperator. As most of these filters are of the paper element type, they give a restriction to flow as a pre-filter, moreso as they become blocked, they work better under pressure. Let's discuss this further, I think it will be interesting!
Mike
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bobclevenger
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The best solution I have for getting quick starts after sitting unused for a lengthy period is to fit an electric fuel pump (preferably near the fuel tank). This will pressurise your fuel system prior to starting the engine. It will also make your car immune to vapour-lock (if mounted at the tank). You may choose to remove the mechanical fuel pump as it is no longer required, or to retain it for a more nearly original look under the bonnet.
All original filters should remain in place.
All original filters should remain in place.
Bob
1972 SP 132/5577, aka "Pirate Jenny"
"Shall we kill them now? ... Or later?"
1972 SP 132/5577, aka "Pirate Jenny"
"Shall we kill them now? ... Or later?"
Wallace not sure about me adding anything further that could be considered useful as I'm usually at the outer edge of my knowledge envelope when fixing 'stuff' on the Jensen. However I have investigated the fuel pump and may have found that the reason for the excessive churning could be the fuel pump. I can't get the car started at all at the moment, so after disconnectimg the fuel line into the carb and cranking the motor I only get a pathetic dribble of motion lotion. I will hold on removing the fuel filter until I get a new pump and try that. The pump fitted at the moment is the cheap Federal Mogul type so I'm looking to fit something a bit more meaty that can take the job on!
Well after replacing the fuel pump with the same type there was of course no difference. Head scratching and a call to our Jensen Guru and a possible cause was identified, a worn fuel pump rod the only part of the engine that wasn't renewed. Typical. A new one was fitted and hey presto loads of fuel and a very quick start. It doesn't take too much to be worn from these rods before the output from the pump is affected. Only 0.2" and there will not be enough push on the fuel pump arm to suck fuel from the tank. The rod should be 3.2" in length. How is this possible on a rebuilt engine? Well after a call to the builders it seems that they never replace these rods, as this problem has never occurred before in their long experience of American engine rebuilding. Looks like we all learn something new every day. The point being that it isn't the destination that's important with Jensen ownership but the journey itself......amen