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Purge Pump.. alternatives?

Posted: Thu Nov 25, 2021 11:24
by Zaphod
Me again! looking at the purge pump it was obvious that it had been opened up, it was also obvious that it was not working when 12v was applied to it. I took it apart and found an old MFA (Model Flight Accessories!) motor in it, loose and not really attached to much and a lot of black dust.. the motor does however work but it's unlikely the original and even less likely to do much as the shaft is way too small for the pump.. (the motor literally fell out when I got the unit open). So I guess it's as dead as the infamous parrot. While I know its not overly important I would like to put something else in its place to do the same job, has anyone found anything suitable?

On another subject, I have the breather 'valve' back on the block, and one end fits to a pipe to the air cleaner, and I have that, but I do not have the pipe that attached the crank case breather to the thermal valve at the back of the inlet manifold, what size pipe is this, it looks to be different diameters at each end?

Re: Purge Pump.. alternatives?

Posted: Thu Nov 25, 2021 11:30
by hodders

Re: Purge Pump.. alternatives?

Posted: Thu Nov 25, 2021 12:35
by Zaphod
Hi, I was reading that which was why I took a look at it, but I think the actual pump end is too far gone

Re: Purge Pump.. alternatives?

Posted: Thu Nov 25, 2021 14:03
by AndyC
If you were to replace the whole pump then it would need to be something that is pretty much sealed from the electrical part to the part holding air/fuel mix. Perhaps not a perfect hermetically sealed arrangement but at least one that reduces the potential for an explosive mix where the motor may spark.

Re: Purge Pump.. alternatives?

Posted: Thu Nov 25, 2021 16:18
by bash
My older car never had one from new and I dont think I missed it either......add lightness and bin it.
Bash

Re: Purge Pump.. alternatives?

Posted: Thu Nov 25, 2021 17:44
by AndyC
They do make a noticeable difference in one situation. Warm engine left for the right/wrong (PoV thing) time.
If the engine is cold, then no need. If the engine is warm and left a long time, no need. If the engine is warm and only left a few mins, no need. it's that period of time where a lot of the petrol in the carbs has evaporated but stayed in the airbox / venturi, before dissipating further. Try and start the car then, and you get a too-rich mixture, especially if you allow the carbs to be completely refilled by the fuel pump. In those set of circumstances, the purge pump will have basically vented that rich mixture to atmosphere, and you'll be OK to start normally.

Re: Purge Pump.. alternatives?

Posted: Thu Nov 25, 2021 18:00
by Hawaiis0
I did a repair to mine and got it working . I did notice a difference with the hot stars

Re: Purge Pump.. alternatives?

Posted: Thu Nov 25, 2021 23:49
by bash
Perhaps the later jets made a difference but I never had a problem hot or cold. When it was hot I held the throttle open slightly when cranking but it never failed to start or gave a hint that it wouldnt.
Bash

Re: Purge Pump.. alternatives?

Posted: Fri Nov 26, 2021 01:16
by Lotus-e-Clan
The classic need for this device is to save face after filling-up with petrol (especially on a hot day -but not exclusively so). You return to the car after paying for petrol, and it won't start (airbox fumes = too rich as pointed-out previously) . And the bloke who was previously admiring your car from the neighbouring pump notices you churning the engine, turns to his partner, and says "Ha! LOTUS, Lots of trouble...".
If you're thick-skinned, you don't need it as Bash says. :wink:

You can replace the purge pump with an alternative, but I do recommend modifying the circuit so you can switch it off when you intend not to restart anytime soon. This is to save the purge pump motor from overheating when running-on too long.

Mine is an aftermarket in-line washer motor with the supply connected to the central locking circuit. The circuit is adapted to cut the supply to the pump when locking the doors (ie when you leave the car for long periods)

Unlike the Lotus OE pump, the aftermarket pumping section is already isolated from any sparks generated by the pump motor, so there is no issue with saftey (fume ignition). The OE Lotus pump was designed to fail because the method of isolation actually overheated the pump (no ventilation) - must have been designed on the back of a fag packet by a Drawing Office slave under pressure.

I replaced mine many years ago and it's proven 100% reliable.

If fact I filled up with petrol today in CattericK (E5 = £1.55!! :shock: ), and it restarted on the button.
Sooo glad, because I'm pretty sure that those Army lads and lassies filling-up their BMWs were willing it to somehow fail just so they could 'take the P' :wink: .

Re: Purge Pump.. alternatives?

Posted: Fri Nov 26, 2021 13:25
by DavidOliver
I am sure Colin Chapman would cringe at the thought of a purge pump, my 85 has no such thing and here in Malaga I have not had any starting hesitation.
Anyhow, flush the airbox with an open throttle, no pumping. I don´t like electrics around fuel systems.


Dave the cog.

Re: Purge Pump.. alternatives?

Posted: Fri Nov 26, 2021 17:13
by Tanz
DavidOliver wrote:
Fri Nov 26, 2021 13:25
I am sure Colin Chapman would cringe at the thought of a purge pump, my 85 has no such thing and here in Malaga I have not had any starting hesitation.
Anyhow, flush the airbox with an open throttle, no pumping. I don´t like electrics around fuel systems.


Dave the cog.
Mine broke 24 hours after buying the car in 2007. Haven't bothered to replace it as it's such a small problem. As you say Dave - just put your foot to the floor and hold it there till it starts as if you had flooded the engine. Starts pretty quickly.

Re: Purge Pump.. alternatives?

Posted: Fri Nov 26, 2021 20:12
by Lotus-e-Clan
If I ever I get myself to a meeting one day (say a LITP), I'd organise a 'hot start competition'. ... a timed event.
It would go like this:
  • 1) Everyone warm their engine by idling until the fans cut-in.
    2) Switch-off and leave for 3 minutes.
    3) prepare to start as you would normally (open throttle or closed)
    4) One turn of the key to restart the engine ...and the key turn must last 1 second or less( ie one flip turn)
My guess is that the purge pump users will win because it will start on the button, like a modern.

Never gonna happen 'cos I don't go to car meetings. It would be a hoot though, especially after a pint or two in the car-park. :lol:

And I don't mind failing, all part of the fun! :mrgreen:

Re: Purge Pump.. alternatives?

Posted: Wed Dec 01, 2021 14:47
by robertverhey
Something like this would do the job I reckon

https://www.ebay.com.au/itm/High-Torque ... 635-2958-0