Lotus Elan

New Mechanical Fuel Pump

PostPost by: 111Robin » Tue Oct 04, 2022 12:26 pm

I purchased a new pump from one of the well known suppliers a few months ago for my Plus 2. Comparing it with the pump I removed (not an original), there is approximately 8mm of travel in the lever arm before it starts to operate the valves. On the old pump there is almost no free movement, it immediately starts to function when moved. Both arms sit at the same position to start with. Can anyone else confirm if they have a pump showing a similar issue ?. I have to assume that this would result in a very inefficient operation, unless there is sufficient offset in the cam to overcome this "slack" ?.
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PostPost by: snowyelan » Tue Oct 04, 2022 2:00 pm

When I replaced my pump recently there was a fair bit of preload against the cam lobe. Can you put the old pump back on and try to determine if you have the same preload? The new pump may have the 8mm of slack taken up by this.
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PostPost by: Craven » Tue Oct 04, 2022 2:53 pm

Pre-load is a good description on fitment, there is quite a push down on the pump to align the fixing holes.
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PostPost by: 111Robin » Tue Oct 04, 2022 3:06 pm

Yes I understand the preload aspect when fitting the pump, however, both pump levers have the same standoff relative to the pump face so irrespective of the installation preload, there is 8mm of travel on the new pump that is doing nothing when compared with the old pump.
I should also add that on the new pump the ports can't be oriented correctly. The outlet port faces into the block at an angle that puts a severe bend in the fuel line going to the carburettors. I removed the screws thinking I could just rotate the top to suit, as you can on most other pumps, but on this one the valves are fixed to the lower body so there is no means of rotating the outlets. Pretty useless really but as usual " no one else has complained".

https://youtube.com/shorts/Yx55PR_bdKI
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PostPost by: Craven » Tue Oct 04, 2022 4:12 pm

It’s a long time since I looked at this but I think all that is happening here is the stoke of the diaphragm is moved to a different place, after all it’s the suction/pressure that operates the valves.
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PostPost by: snowyelan » Tue Oct 04, 2022 4:28 pm

The replacement pump in you video looks about the same as the one I have, supplied by RD in the States, which is working fine. I re-plumbed the fuel system, so the cap orientation was a non issue for me

I wonder if the free play has something to do with incorporating the primer lever mechanism?

The mounting face isn't the important bit. The vertical distance between the bolt bores and the cam lobe is. The 8mm of free play is irrelevant unless it falls within the lobes working window.
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PostPost by: gjz30075 » Tue Oct 04, 2022 4:41 pm

I have the same amount of play in my aftermarket (RD) pump. It works fine when installed but I removed
it for the same reason Robin mentioned. The outlet port points toward the engine which puts a severe
bend in the fuel line. Orientating the the output port to the next position counterclockwise puts the
port facing the footbox.
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PostPost by: 111Robin » Tue Oct 04, 2022 5:00 pm

Time will tell. I've driven the car four times and been recovered by the AA each time. Diagnosis was originally ignition but replacement of each item made no difference. Fuel starvation was more likely, tank is clean, new lines, new pump (as per this post), carbs fully overhauled (this was all done before I drove it and broke down). Since the last failure I removed the carb covers, no dirt, cleaned the filters, again no dirt, and pumped the tank dry, no dirt retrieved. So I figured I'd remove the pump to check it and this is when I found the difference between this and the old pump. I've refitted the old pump and I'm trying to pluck up courage to take it for a test drive. If this doesn't solve it I'm at a loss.
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PostPost by: ericbushby » Tue Oct 04, 2022 5:10 pm

Hi Robin,
When you say that you replaced all the ignition components did that include the rotor arm. My car would leave home running smoothly, run for half an hour and then would not go home. Just checking because I have been there.
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PostPost by: 111Robin » Tue Oct 04, 2022 5:19 pm

Eric,
I replaced it with a rotor arm from the Distributor Doctor, original Lucas cap, new leads, new coil and new Aldon Ignitor. I hate replacing parts without good reason but just can't diagnose this fault. It certainly feels like fuel starvation (tank is definitely not vapour locking) but the time to failure varies as do the driving conditions. It doesn't fail pulling up a long hill for example, but on the flat at light throttle or just anywhere basically. It spits back a few times then goes down on power until it can't take any load at all. Roadside checks are confusing as there is fuel delivery at the carbs and there is ignition. Hopefully the pump is the issue (although I now have my doubts) and it just wasn't delivering sufficient fuel over time at which point it starts to run weak and cuts out. I hope.
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PostPost by: Donels » Tue Oct 04, 2022 5:50 pm

Carbs spitting back before stopping is a clue. This usually happens on webers (not sure about Dellorto's) when the fuel level runs low. I would suggest it is a pump problem.
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PostPost by: alan.barker » Tue Oct 04, 2022 5:59 pm

Craven wrote:Pre-load is a good description on fitment, there is quite a push down on the pump to align the fixing holes.

That depends if you have turned the Engine so the Fuel Pump Cam is at it's lowest postion to make fitting Fuel Pump easier.
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PostPost by: 111Robin » Tue Oct 04, 2022 6:06 pm

Donels wrote:Carbs spitting back before stopping is a clue. This usually happens on webers (not sure about Dellorto's) when the fuel level runs low. I would suggest it is a pump problem.

I really hope so, I'm at my wits end with this.
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PostPost by: gjz30075 » Tue Oct 04, 2022 6:38 pm

You might try installing an electric fuel pump, temporarily, in the boot.
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PostPost by: ericbushby » Tue Oct 04, 2022 7:05 pm

Robin,
The suggestion of a temporary pump in the boot is a good one. A cheapo. facet cube look alike is about £14.00 on ebay and will work any way up.
I have one of those fitted just for priming the Webers Just consider the fuel pressure may be higher than usual, but it would provide more information.
Eric in Burnley
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