Lotus Elan

Stumbling Dellorotos

PostPost by: vxah » Tue Nov 01, 2016 8:56 am

Gradually opening the throttle under load and it dies? Isn't going to be the accelerator pumps, Whole thing dies when accelerating, not just loss of one or two cylinders? Your not likely to get dirt block all 4 main jets at once?
Lack of fuel supply to carbs... Full load, float bowls run dry as supply can't match demand, engine dies.. Back off throttle, trickle of fuel is enough to keep float bowls topped up and keep running.. If you are sure the fuel pump is good fit a "T" piece into the fuel line before the pump and attach a vacuum gauge with a long enough hose that you can mount it to be visable while driving... Go for a thrash and if you start to pull vacuum when it dies, you need to look at the tank? Some vehicles can pull air into the fuel line but I think that's unlikely on the Elan as the tank is higher than the line so a fuel leak would be evident when not running?
Just me thinking what I would do although I would probably have fitted a fuel pressure gauge on the feed to the carbs, not easy though due to the low pressure used.. That and connecting it safely.. Another thought, give it some stick on the road until it cuts, soon as that happens kill the ignition and coast to a stop in neutral, pop the lid off a carb and see the fuel level! If it's normal full level forget everything I wrote ;-)
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PostPost by: frogeyesimon » Tue Nov 01, 2016 12:09 pm

Some good tips here I think.

It's definitely more of a total power loss than a misfire and it only seems to happen when the car has been driven hard for a couple of miles.

Accelerator pumps all look fine and squirt petrol as I'd expect. Nothing is stuck, no leaks, small ball bearing in valve is free to move, all rodded-out and blown-through, no crud anywhere, diaphrams look sound.

Just as you say "Your not likely to get dirt block all 4 main jets at once?" - it also seems to me to be unlikely that both sets of accelerator pumps would fail at the same time....

Next time it happens I will do the "freewheel to a stop with ignition off" and check the float levels.

I'm becoming ever-more convinced that the fuel pump is not delivering sufficient volume of fuel. Perhaps now is a good time to change to an electric pump. If for no other reason than it should make starting after prolonged lay-up periods easier.

Simon
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PostPost by: ncm » Tue Nov 01, 2016 12:47 pm

I had a similar problem a few years ago. I bought the car as a non-runner..seized engine..and when I got it back on the road I experienced the same symptoms. As suggested above, check for fuel in the float chamber when it cuts out. The cause in my case was crud in the fuel tank blocking the outlet. ISTR that the outlet union sits in a slight depression in the bottom of the tank...

Brian.
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PostPost by: billwill » Tue Nov 01, 2016 7:38 pm

alan.barker wrote:Clean and make sure accelerater pumps are not seized in bottom of carbs
Alan



There's a spring-loaded teenie teenie, ball bearing valve at the bottom of the accellerator pump on a dellorto; be carefull not to lose any bits.
Bill Williams

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PostPost by: toomspj » Tue Nov 01, 2016 9:55 pm

From what you describe, it does sound like fuel starvation. If car is ok for a mile or so before it fails, then it sounds like the fuel isn't filling the float chambers fast enough. I once had a similar problem which I traced to an air leak on the fuel line upstream of the pump which stopped it getting good suction. I presume you're reasonable sure that the pump is working ok? Alternatively, could you have blocked suction line (in tank or in a filter), or (less likely my view ) a block fuel tank vent?

On my race cars I fit a Rebco fuel pressure warning light (you can purchase them from US) which massively cuts down the diagnosis time for is it fuel or is it ignition. The switch conveniently screws into a Filter King pressure regulator. If you do fit an electric pump, you might well want to fit a regulator too or else you risk flooding the carbs.

Paul
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PostPost by: frogeyesimon » Wed Nov 02, 2016 8:26 am

I'm struggling with determining whether the fuel pump is delivering an adequate volume of fuel. After I stripped everything down at the weekend, the carbs were completely empty of fuel. It took the best part of a minute of engine cranking before the car would fire, so I'm guessing that most of this time was taken filling the carbs. Is this about right? - it seemed like a long time to me.

Simon
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PostPost by: ericbushby » Wed Nov 02, 2016 9:41 am

Simon,
It seems a long time to me also.
I would have expected the accelerator pumps to have worked much sooner than that and the engine would have started on them until the carbs reached the correct level to supply fuel normally.
My experience is with Webers.
I had random intermittent breakdowns at one time. The car would leave home happily, but didn`t seem to like going back. It was some time before I found on one occasion that the float chambers were empty.
The pump was obviously quite old and not the glass top version, so I bought a new one from Sue and it has been OK since.
I tested the old pump but could not make it fail. I pumped water manually up a plastic tube fixed to the house wall with no problem. I suppose It only needs a piece of grit or a weakness in a valve to cause a failure.
If you are sure the fuel supply to the pump is adequate then I suggest you replace it.
If the old pump is original, then keep it for the next owner.
Eric in Burnley
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PostPost by: Orsom Weels » Wed Nov 02, 2016 9:57 am

A minute is a hell of a lot of cranking to get fuel up, with a good pump & supply line I would expect no more than 15-20 seconds. That should be plenty of time to provide enough fuel to make it start if not brim the float chambers to the top. I would check the supply from tank to pump, make sure there is no possibility of air being sucked in, if that's all good, then perhaps time to try another pump.
I have an old Ford Corsair, which has the same pump, I had similar issues & eventually replaced the pump. Now it will lift & start squirting fuel within a few swings of the engine, & the tank is lower than the pump so it doesn't have the advantage of gravity.
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PostPost by: persiflage » Sun Nov 06, 2016 8:46 pm

Simon,
My experience of fuel starvation on Dellorto.
Attachments
image.png and
Fuel starvation.
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PostPost by: frogeyesimon » Mon Nov 07, 2016 8:32 am

OK, I got there in the end. It was as simple a problem as a blocked tank-pump fuel line. The intermittant way in which it presented itself made diagnosis rather confusing. Anyway, for my efforts, I now have a car which starts and runs far better than it did before, largely, I suspect, due to the fitment of electronic ignition and the other new ignition bits.

Thanks for all your contributions
Simon
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