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Special Sports fuel issue

JT7196
Posts: 1072
Joined: Sat Feb 13, 2016 7:22 am

Re: Special Sports fuel issue

Post by JT7196 » Tue Dec 17, 2019 9:40 pm

Hi, check that the Vent in the Fuel Tank or Cap is not blocked, I had similar problems with my Lanchester , turned 5hat the new Gasket I made for the Fuel Cap needed to have Vents cut into it to prevent a Vacuum building up in the Tank.
I did notice in an earlier thread, that you said that the Corks in the Fuel Valve were “Dry”, this would be indicative of Fuel starvation in the line .

Cheers Al 😊😊😊

Noelex
Posts: 38
Joined: Wed Jul 13, 2016 11:27 am

Re: Special Sports fuel issue

Post by Noelex » Sat Dec 21, 2019 10:19 pm

I have found on all my old cars that it is essential to acid treat and ReCoat the fuel tank. All old cars have rusty dirty fuel tanks. Even relatively good tanks contain significant debris which will effect reliability. I have often found that tank breathers are also blocked or partially blocked. Many people blame mechanical fuel pumps when in fact the tank, fuel lines or breather are in poor condition. I also replace all flexible fuel lines if they are over 10 years old and check them when they are newer. Modern ethanol fuels I found not only destroys old rubber and seals but also new stuff that is supposedly suitable but actually goes brittle. Very much belt and braces. But worth it. Cheers and Happy Christmas or Happy celebrations all..
Hugh Spencer

Crossley Stephenson
Posts: 251
Joined: Wed Feb 10, 2016 9:15 pm
Location: Victoria, Australia

Re: Special Sports fuel issue

Post by Crossley Stephenson » Wed Jan 15, 2020 2:33 am

After messing around and feeling relieved that I had fixed the fuel supply problem it returns. Sometimes the AC pump will prime really easily and other times it just won't prime. Everything has been checked and rechecked and I am now giving up in frustration on the AC pump (been rebuilt twice) and going electrical. I intend to mount the electric pump (solid state) in the boot to push the fuel forward. I intend to take the keyed live connection from the fuel gauge sender. My question is: is it best practice to use a relay between the pump and the fuel gauge connection and if so what amperage fuse would I use?

Another question: can I remove the innards of the AC pump and leave it in place - for appearance sake?

Cheers
Michael

Norfolk Lad
Posts: 586
Joined: Wed Feb 10, 2016 8:23 pm

Re: Special Sports fuel issue

Post by Norfolk Lad » Wed Jan 15, 2020 5:08 am

Just wonder if the cam that drives the pump is lifting the arm to the highest point will this stop you working the hand primer, so depending on position that cam has stopped you can or cannot prime carbs.
Try turning engine to allow movement in the pump so you can then hand prime.

qantasqf1
Posts: 149
Joined: Mon Mar 07, 2016 10:13 pm

Re: Special Sports fuel issue

Post by qantasqf1 » Wed Jan 15, 2020 6:59 pm

What’s the ‘keyed’ live connector from the sender unit? Is it the wire that connects to the unit? If that’s what you mean it can’t be used for the electric pump, which needs 12 volts to operate and the tank unit wire’s current varies with the fuel level. A wire from a 12 volt source that is activated when the ignition is turned on is needed. I would doubt a relay for an electric pump would be needed since they draw very little current, although I stand to be corrected on this.
If you fit a pipe completely bypassing the AC pump all its innards can be discarded except the hardened steel pin (plus 2 circlips) that the camshaft operating lever pivots on.
Incidentally, if you bypass the pump, please don’t throw away the lever that the camshaft operates. These vary with the car it’s fitted to so it’s compatible with the DB18.
Steve

Crossley Stephenson
Posts: 251
Joined: Wed Feb 10, 2016 9:15 pm
Location: Victoria, Australia

Re: Special Sports fuel issue

Post by Crossley Stephenson » Thu Jan 16, 2020 5:05 am

Thanks Steve, of course you are absolutely correct - voltage on the wire I was suggesting varies with the level of fuel in the tank. Saved by the Forum again! What I need is a green or white wire that are only live with the ignition on but a quick look at the wiring diagram and I can't find anything suitable at the rear of the car. This is probably why most electric pump conversions I have seen have the pump near the old pump where it is easy to find a feed point. Anyone ahave a clever idea?
Cheers
Michael

Crossley Stephenson
Posts: 251
Joined: Wed Feb 10, 2016 9:15 pm
Location: Victoria, Australia

Re: Special Sports fuel issue

Post by Crossley Stephenson » Thu Jan 16, 2020 5:14 am

There is a purple wire - constant live but fused - that I could use in conjunction with a switch to the pump - an added security feature?

Cheers
Michael

qantasqf1
Posts: 149
Joined: Mon Mar 07, 2016 10:13 pm

Re: Special Sports fuel issue

Post by qantasqf1 » Thu Jan 16, 2020 7:47 am

Not a good idea! It’s not simple to find a terminal that activates with the ignition switch because of that stupid control box- no wonder Daimler discarded it for the DB18 Consort. However, there aren’t any wires that fill the bill at the rear end of the car so a wire needs to be run from under the bonnet or the dash. I don’t have a wiring diagram in front of me, but I THINK the active side of the reverse light switch comes on with the ignition switch, so that would be a good source. I’d run the new wire through a line fuse fitted near the switch as a precaution.
Steve

qantasqf1
Posts: 149
Joined: Mon Mar 07, 2016 10:13 pm

Re: Special Sports fuel issue

Post by qantasqf1 » Thu Jan 16, 2020 11:27 pm

Not a good idea! It’s not simple to connect a wire to the control box terminal that activates with the ignition switch because of that stupid design - no wonder Daimler discarded it for the DB18 Consort. However, there aren’t any wires that fill the bill at the rear end of the car so a wire needs to be run from under the bonnet or the dash. A good candidate for a 12 volt supply would be the active wire to the wiper motor because it activates with the ignition switch and it’s easy to access. (This wire is constantly active with the ignition switched on, the wiper switch itself merely earthing the wiper motor). To identify which of the two wires to the motor is the one you’re after disconnect both wires and switch on the ignition. Only one will be active - that’s the one! I’d run the new wire through a line fuse fitted near the pump switch as a precaution.
Steve

Db n j
Posts: 267
Joined: Sun Mar 13, 2016 8:55 am

Re: Special Sports fuel issue

Post by Db n j » Fri Jan 17, 2020 9:04 pm

Michael, think Norfolk Lad makes a good point- it’s possible to position the fuel pump arm in such a position that the manual priming handle won’t work (the pump works off the camshaft). Before you give up on the mechanical pump, try pressing the starter solenoid to reposition the pump arm, and then try the manual lever.

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