Mechanical v Electric fuel pump?

[David C]

That's an interesting idea but needs some refinement. If you just use a pressure switch then you will get no fuel until you crank long enough to build oil pressure. A less ideal solution than a mechanical pump.

[dwomby]

I agree reverting to the original mechanical pump has advantages but to fit one back in my car now would be a big job and I want it on the road. I'll add it to my list of future 'improvements'.

David

[Kevin H]

I've had a Carter fitted in the boot of my 411. It makes enough noise so you can hear it fill the carb when you turn the ignition on, but once the engine is running you can't hear it. However, they seem to be unreliable and don't like being unused for long periods of time. My first one seized and just got hot - not ideal for a petrol pump, and it's replacement doesn't appear to working properly either. So I can't recommend them.

As for pressure, I don't know what the 313/318 engines need, but the 411 needs 5-5.5 PSI; I have a pressure regulator mounted inline next the carburettor unfortunately I can't tell you what flow rate is required.

As an aside, I once saw a 412 which was fitted with an electric pump which was used just to prime the carburettor before starting by pressing a button in the cabin, but still used the mechanical pump when running.

[AndrewA]

On mine when I swapped from SU to Facet I checked the specs of the carb to make sure I knew what it wanted in terms of pressure and flow. The silver top pump seemed most appropriate for my small block but a red top is probably what you need.
I bought the kit which includes new bobbins etc and a selection of springs from Facet so you can alter the pressure of the pump by unscrewing the bottom of the pump and swapping the spring over.
I had two goes at mounting it until I found a spot where it couldn't vibrate against anything.
On mine it's very quiet (inaudible when running) and I'm happy with it.
I didn't use a regulator and all seems fine.
On previous cars (not Bristols ) I've used them and mounted them in all sorts of places - so I wouldn't worry too much about whether it's below the bottom of the tank or not - they seem to cope.
Hope this is of some use!

[dwomby]

Originally Posted by AndrewA

On mine when I swapped from SU to Facet I checked the specs of the carb to make sure I knew what it wanted in terms of pressure and flow. The silver top pump seemed most appropriate for my small block but a red top is probably what you need.
I bought the kit which includes new bobbins etc and a selection of springs from Facet so you can alter the pressure of the pump by unscrewing the bottom of the pump and swapping the spring over.
I had two goes at mounting it until I found a spot where it couldn't vibrate against anything.
On mine it's very quiet (inaudible when running) and I'm happy with it.
I didn't use a regulator and all seems fine.
On previous cars (not Bristols ) I've used them and mounted them in all sorts of places - so I wouldn't worry too much about whether it's below the bottom of the tank or not - they seem to cope.
Hope this is of some use!

Thanks, Andrew. Supply chain issues have led me to obtain a Carter P4070 to install this weekend. If it is too noisy or fails, I have a backup on order. I do plan to mount it on rubber 'bobbins' to help reduce noise/vibration. I'll let the forum know how it goes.

David

[David C]

I quite like the idea of an auxiliary low volume electric pump to prime a system with main mechanical pump. It would be easy to control with brief timer as used with diesel injectors. That said it seems to be a fix for an unlikely problem. I understand the concern of pump running and leaking fuel with engine off and ignition on but there are other safety issues I would deal with first. The most notable is lack of headrests in the early V8s but thanks to a suggestion from Giles Parsons I hope to be sorting this soon with some from an MGB.

[dwomby]

Originally Posted by David C

I quite like the idea of an auxiliary low volume electric pump to prime a system with main mechanical pump. It would be easy to control with brief timer as used with diesel injectors. That said it seems to be a fix for an unlikely problem. I understand the concern of pump running and leaking fuel with engine off and ignition on but there are other safety issues I would deal with first. The most notable is lack of headrests in the early V8s but thanks to a suggestion from Giles Parsons I hope to be sorting this soon with some from an MGB.

David, I'd be interested to know how you plan to fit those MGB headrests. I have opted for an easier install that screws into the back of the seat which I believe is wood. There's a pic here http://www.bristolcars.info/forums/8...html#post10710 but they are not installed yet. I suspect the MGB ones would probably provide better resistance to a whiplashing head.

David

[Kevin H]

Originally Posted by David C

I quite like the idea of an auxiliary low volume electric pump to prime a system with main mechanical pump. It would be easy to control with brief timer as used with diesel injectors.

I don't see the need for a timer, unless you want it be fully automated with the ignition switch. You could just use a momentary on-off switch, which you press for a few seconds to fill the carburettor before depressing the accelerator pedal and engaging the starter motor, (ideally a reduction gear starter motor).


It may only be required when starting from cold when the car hadn't been used for a long time.

[dwomby]

Originally Posted by Kevin H

I've had a Carter fitted in the boot of my 411. It makes enough noise so you can hear it fill the carb when you turn the ignition on, but once the engine is running you can't hear it. However, they seem to be unreliable and don't like being unused for long periods of time. My first one seized and just got hot - not ideal for a petrol pump, and it's replacement doesn't appear to working properly either. So I can't recommend them.

As for pressure, I don't know what the 313/318 engines need, but the 411 needs 5-5.5 PSI; I have a pressure regulator mounted inline next the carburettor unfortunately I can't tell you what flow rate is required.

As an aside, I once saw a 412 which was fitted with an electric pump which was used just to prime the carburettor before starting by pressing a button in the cabin, but still used the mechanical pump when running.

Sorry to hear that , Kevin, especially as a Carter is what I just took delivery of and plan to install this weekend! My first two choices were back ordered so I ordered the Carter P4070 as it's pretty inexpensive and I could have it now. If it fails, I still have my first choice of a Mallory Comp 70 on order or I might even try a Carter-clone.

David