Will not run once hot.

[M.J.S]

As a long 'refresh' draws to an end after too many years, with virtually everything on the car now new or fully reconditioned, I want to put some miles on her, but have encountered a problem.
The engine is fully rebuilt, with all the induction and ignition also either new or professionally rebuilt. She starts usually first time, ticks over well, revs cleanly and sweetly and pulls like a train, oil and temp both where they should be.
If she gets hot enough for the fan to cut in, weather, traffic or left to idle, etc, after a few minutes she will suddenly cut out. She will restart at first, but will start to fluff if the throttle is blipped, runs increasingly erratic and will keep cutting out until after a few more minutes of this, she will refuse to restart at all. Left for ten minutes she can be coaxed to restart but again, runs poorly. If left to cool right down, she will start first crack and run like a dream - until she gets hot again.
When hot and she refuses to restart, she has a strong spark, the compressions are fine, there is fuel getting to the carbs, but it almost feels as if she has run out of petrol. Just a gut instinct, I might be very wrong.
Tank and fuel lines have all been flushed, carbs are professionally reconditioned, fuel pump is brand new as are all the lines and mounts, etc etc.
Driving me crazy guys. Anybody had a similar issue?
Many thanks.

[alan.barker]

Imho HT Coil. They are not expensive and if it's not that a spare is always handy.
Are you running Points and Condenser or Electronic Ignition.
If running Points get a good Condenser from Distributor Doctor also.
Alan

[Craven]

I had a faulty electric fuel pump that caused very similar problems, a Facet Solid State.

[ericbushby]

Hi MJS
+ one on the pump.
Check your fuel level when it is misbehaving. I had a fuel pump which worked perfectly except when it was a long way from home. With Webers take out a main jet stack and you should be able to see fuel with a small torch. I don`t know about other carbs.
The other quick and cheap one is to replace the rotor arm. They are quite well known for doing just that.
Mine failed after half an hours running when fully heat soaked and recovered when cool.
Best of luck. Let us know how you get on.
Eric in Burnley
1967 S3SE DHC

[englishmaninwales]

+1 on HT coil.

[AussieJohn]

I had a condenser that caused this.

[M.J.S]

It is electronic ignition and the coil is brand new, as is the distributor and all other ignition components. When it's cut out and wont start, pulling a lead and slotting in a spare plug to check, the spark is bright and constant.

I have just fitted a brand new mechanical fuel pump as I thought it might be the issue myself, but it hasn't made any difference whatsoever.

The car is on its original Dellortos, now professionally reconditioned.

It's so sweet until it gets hot, then the change is quite rapid, from crisp to crap in a matter of a minute.

Witz end.

[Craven]

Bummer
Not often adhered too but the carburettor union ( feed ) should be the highest point in the supply.
This avoids air locks from fuel evaporation etc.

[alan.barker]

Put old Coil back and try.
If not refit old Condensor.
The last Condensor on my Sprint lasted 50 miles, Chinese crap. Now i have Simonbloc hall effect and no problems for 6 years.
Alan

[69S4]

Thought it was Strombergs to begin with

The wrong rotor arm did stuff very similar to that on my car years ago. It got past an auto electrician but the AA man spotted it in seconds at the side of the road.

I had a failing condenser give similar symptoms but only once and then it was undriveable, not time after time. Clean the points and then it would run for a minute or two.

[Matt Elan]

The problem is that 90% of fuel problems are electrics and vice versa and are difficult to diagnose, especially remotely
I would suspect it’s the coil as a first call - even new ones can fail, so swap it and see if anything changes. Then do the same new plugs, then the distributor cap, then rotor arm then hit leads and caps.
The restarting instantly when cold makes me think it’s electrics, the fluffing as it dies again says something’s breaking down due to heat soak.

[M.J.S]

Lumination electronic ignition in brand new distributor, therefore no condensor, ballast ignition (new) and Lucas sports coil (new) rotor, cap and leads (all new) and as far as I know, not Chinese shite, sourced from reputable companies. Not to say something isn't duff, it's just feels fuel related, like petrol isn't getting through. Spark is excellent when cranking cold or hot, just makes no attempt to start once hot, almost like there is no petrol in it.

[mbell]

Try some easy start to confirm if spark or fuel?

Have you pulled a plug when it cuts out to check condition?

Have you tested the fuel pressure? I've seen reports of new pumps with too high pressure. If it too high it could be overfueling and choking up your plugs etc. Probably never start with bad plugs and flooded engine.

[Esprit2]

Ignition components are heat sensitive, so I haven't discounted them as causing your problem. But you state they're all new, so I'm not going to argue the point. But I'm also not saying, "they're all good, move on". I still have my doubts.

Similarly, the mechanical fuel pump is new, but what is the fuel pressure at the carb inlets? 'T' a fuel pressure gauge into the fuel line as close to the carb inlets as possible to measure the 'running' fuel pressure. The Dellortos like 1.5-2.5 psi, and can tolerate 3.0 psi. Higher than that, and excessive pressure could be forcing fuel past the inlet needle valves, resulting in an artificially high fuel level. The carbs could still be tuned to run well that way, but there would be very little margin for further fuel level changes. Then the engine gets very hot, as do the carbs, the fuel expands, the mixture goes over-rich, and the engine bogs down. Check the fuel pressure at the carb inlets.

Back in the day, there were three different floats available... 7, 8.5 & 10 grams. And each float had it's own Float Height spec. Correctly installed, each weight with it's own height, they all produced the same fuel level. The difference was in how floats of different mass reacted differently to changes... subtle stuff beyond the scope of most back yard tuners.

According to Lotus TSB 1973-10, the Elan Twin Cam's float heights should be:
Early DHLA 40 = 10 gram floats set to 14.5 to 15.0 mm height.
Later DHLA 40E = 8.5 gm floats set to 16.5 to 17.0 mm height.

At least one of the original weights is no longer available. And of the two that were available the last time I checked, they were reproductions made from new tooling. So...

1) Which DHLAs are installed? 40, or 40E?
2) What weight of float is installed? It's engraved on the top side of the float, so the float will have to come out in order to read it.
3) To what heights are the float's set?

"IF" whoever rebuilt the carbs could not get a float of the original weight, substituted another weight, but still set the Float Height by the book, then the fuel level could be incorrect. And it's Roulette as to whether he err'd high or low. "IF" the fuel level is high, and the carb tuned to run normally when temperatures are low-normal, then the carbs could sensitive to high heat, and be more prone to going overly rich (engine bogging down or flooding out) when the engine runs 'HOT'.

Regardless of float heights and weights, it's important for the fuel "LEVEL" in the float bowl to be correct, at 27mm down from the top of the jet pedestal, with the carb's top cover removed. As the cover is removed, lifting the floats out of the pool causes the fuel level to drop. The 27mm Fuel Level is with the carb's top cover off. There's a higher / smaller number value that applies when the top cover is installed, but I don't recall that at the moment. So you're stuck with the 'cover off' measuring method, as follows.

1) Remove the cover, and remove both "Main" jet assemblies from the carb. Use a syringe of small scoup/ spoon to remove some fuel from the bowl until it is definitely below spec height. Replace the top cover without re-installing the Main Jet assemblies. For start up and idle, the carbs run of the Idle Circuit, and the Main Jet assemblies won't be missed... as long as you don't open the throttle wide, or attempt to drive the car that way.

2a) Either switch the ignition ON and allow the electric fuel pump to run until you hear it slow, indicating the float bowls are full and the inlet needle valves have closed, or...

2b) Start the engine, and allow it to run long enough for the mechanical fuel pump to fill the float bowls to the point that the inlet needle valves close. You won't hear the pump slow, as with an electric pump, so just guess on the long side. But don't run long enough for the engine to get hot enough for the heat to affect the carbs.

3) Disconnect the fuel lines from the carbs' inlets to vent any residual line pressure, and to drain any fuel in the carb inlets external to the needle valve. When the top cover is removed again, the floats will drop as it is lifted, the needle valves willl open, and any residual fuel pressure, or excess fuel pooled outside of the inlet needle valve, will result in more fuel pee'ing into the float bowl as the cover is lifted, producing a false fuel level to be measured.

4) Remove the carbs' top covers... pausing to hold them over their float bowls so fuel can drip off into the bowl.

5) Measure down into the two empty Main Jet wells in each carb. Since engines and/or carbs are often mounted off-level, low to the rear, the fuel level will be different at the front and rear of the bowl. So measure the fuel level in both jet wells, and average them.

Use a vernier/ dial/ electronic caliper. As you open the jaws, a 'stick' extends out of the back of the caliper's long body. That's a depth gauge. Stand the caliper on it's end on top of the jet pedestal such that the depth gauge 'stick' extends down into the Jet well to 'just' touch the surface of the fuel. Read the fuel level dimension for each Main Jet well, and average. 27mm is correct. A smaller number value, like 25mm is too high. A larger number value is too low. You want 27mm. If the level is incorrect, adjust the float height accordingly.

Yes, measuring the fuel level is a pain. The caliper and your hand are both in your line of sight, making it difficult to see when the depth gauge 'stick' touches the surface of the pool. If you simply can't do it, then measure over the side of the jet pedestal, front and rear and average the readings (this is a compromise, and not as accurate, but it's more doable). The fuel's surface tension will cause a 'fillet' radius to form right where the fuel meets the pedestal wall. Measure out from the wall far enough to avoid that radius, yet keep the 'stick' parallel to the side wall.

When you have established a correct 27mm fuel level, carefully measure and recored the resulting float height for future reference.

Oh man, that got long...

Regards,
Tim Engel

[alan.barker]

I fitted a new all metal fuel pump once and it produced too much pressure. It run very bad when hot. I had to fit a pressure regulator to fix the problem.
Alan