Lotus Elan and Lotus Elan Plus 2 Forums

I had to call a recovery truck for the first time after 18 years of +2 ownership.

Coming off the A130 in 24 degree temperatures and after a fast run I stopped at the roundabout on the A127 and the car stalled and then refused to start. Some kind souls helped push me to the central island, and I spent the next 30 mins trying to start the car. It would fire once or twice but would not run.

Looking at the clear inline fuel filter it was nearly empty, although there was fuel in the glass bowl of the mechanical fuel pump. I then had to call a breakdown truck, and while we were waiting an hour later I tried again - still no joy.

We were taken home and after a further 2 hours I tried again and the engine started and ran normally! The fuel filter was full.

I was running Tesco 99 momentum fuel, and have an original spec fuel pump feeding Strombergs though a clear fuel filter.

Was it vapour lock? (never had it before), and is their a way to confirm it and eliminate it in future?

Dave Chapman.

A. electric fuel pump

B. Keep the mechanical pump and make sure you have the correct gasket/spacer (105E9374) in place to insulate the pump from the block heat. If it happens again pour cold water over the pump to cool it down and wait a bit.

C. I would guess that the priming bulb that some install to overcome the fuel evaporation in the carbs would also push the fuel past the vapor lock in a pinch. ...but that would just be a bandaid for the problem.

Glad you got back ok but it does knock your confidence when the car lets you down like that. Tbh though 24 degrees isn't that hot. I'd have thought for some of our colleagues that live in warmer climates it would be a cool day. If vapour lock is a systemic problem they must have found ways round it. (if they have answers to carb icing in winter I'd like to hear those too )

Having said that I've had so many of those symptoms on my Stromberg S4 over the years (including stopped at the side of the road until it cooled down). I took a brute force approach to it including (first) electric fuel pump and (eventually) pre engaged starter to try and get past the fires once and then stops issue. My GP wife once had to get the patients family to bump start the car when she used it for a home visit.

It still happened occasionally until I rebuilt the carbs. On strip down I found the bias spring on one of the needles had broken causing the carb to run v rich and the temp compensators stuck shut. Since the rebuild its been fine but there's still a will it start heart flutter after 15 / 30 mins of hot shutdown.

Thanks for that both of you.

The only new thing about my setup is the first time use of the Momentum 99 fuel. I went to Norwich 100 miles away and back in similar temperatures with no issues just 2 weeks ago. That was on unleaded 97 fuel.

I am trying to find out the comparative vapour pressure figures for the Tesco Momentum fuel, Esso unleaded 97 fuel and Esso unleaded 95 fuel. before this week I used the last two fuels with no issues.

Dave.

I forgot to mention in the post I just made regarding expectations for modern fuel, but in watching an episode of Jay Leno's garage (on the 1966 Lincoln Continental) he (and the Lincoln guru he had on the show) noted that cars like the Continental that were marginal on vapor lock (this car used an OEM circulation system of fuel from the tank to cool the carb and there were aftermarket fuel pumps that did not have the necessary fittings) have more severe vapor lock issues with modern U.S. fuel. As you see more ethanol across the pond, expect the same.

Don't know that the Twincam should be considered marginal on vapor lock, but it's worth consideration.

I have suffered these problems initially on my Dellorto carb S4. I decided to route the braided pipe from the pump to the forward carb further away from the engine block. Also, both times my car suffered this problem I didn't have an awful lot of fuel in the tank. So far I've not had this problem occur again.

I don't have the vapour problem in my +2 because I put fuel injection on it but I foo have vapour lock on my elite type 14, i solved this by wiring a fan into the intake and ducted cool air on to the carbs, modern unleaded is not petrol and will only get worse as more ethanol is added into the mix soon

Definitely need the pump spacer.
Maybe your filter provides a nice warm place for fuel to sit and pick up radiant heat especially when there's no air flow around it. If you run straight to carbs you may get better results?
I've always found UK fuel very clean. Whenever I've changed fuel filters on mainstream cars after 100k miles they always look as if they'll do the same again.
The fuel pump has a gauze fine enough to save blocking carb jets doesn't it?

This thread may help.
lotus-carbs-f40/vapor-lock-think-t29160.html

Hi Dave,
I had a similar problem years ago with my +2 running on D'ellortos. It was years ago and you may already have cured this problem, but for me it was the tips of the fuel inlet valve in the carbs. They had worn such that a step was formed, When it was cold, no problem, but hot, it would not start. I seem to recall that I fitted "viton tipped" valves in the carbs and have not had a problem since.
Worth checking?
Also,not teaching you to such eggs, but did you try and start it with your foot planted to the floor on the accelerator? Always do this when the engine is hot.

Kind regards
Jeff 72+2

Be careful not to mix 2 different problems.
You can have vapour lock (no fuel) or heat soak (causes flooding).
A modification they did on TVR cars is to have a return from Carb to Tank so there is always flow and supply of cool fuel to Carb. You can also fit an electric Pump in the Fuel line to be switched on when there are vapour lock problems (hot weather)
Alan

Thanks again everyone.

When I broke down I took a spark plug out - it was dry, so I assuming a vapour lock problem, or something intermittent with my pump.
I tried out an old Moprod pump that was fitted in the car when I got it back in 2000. When I started it up everything worked, but the pump sounded like a castanet party under the bonnet - much too loud to be acceptable.

So I have gone back to basics, and dumped the paper fuel filter after the pump. I just have a sintered element filter between the tank and the pump. Although the paper filter does not look too dirty, I am wondering if the back pressure from the filter was enough to disrupt the pump flow and accentuate a vapour lock problem.

The pump does not have a spacer - so that will not help. I have spacers but I recall that the pump arm did not look long enough to use one when I fitted it. Are there different arm lengths?

Anyway I have had the pump in for over a year without a problem before yesterday, with plenty of hot journeys.

So I will try some test runs - with plenty of cold water in the car - and see what happens. It could still be the Momentum fuel.....

Dave.

My worry would be that if it really is the difference between one fuel and another causing it that things are really marginal down there.

I use Momentum from Tesco at Dunmow, not a million miles fro where you were. I've been using it for a long time and never experienced a similar problem, though I do have an electric fuel pump (and would never go back to mechanical, apologies to purists). My suspicion would be a problem with the mechanical fuel pump diaphragm rather than the fuel itself.

Sorry Dave I forgot to mention in my previous post that when I had this problem I had also fitted an additional cylindrical glass fuel filter near the fuel tank. I decided to remove this as it might have helped to cause the problem. In hindsight I don't think any extra filters are required on top of the fuel pump and carb filters. Regards, William.

I have removed the plastic filter, so there is just the pump and R9 hose going to the t-piece at the carbs. I have kept the sintered filter for the moment. The filter is in an aluminium case - I got it from Burton Power if I recall - nice piece of kit IMHO.

I refurbished the pump itself just a year ago, with a new red diaphragm and new valves - so it should be ok.

I went for a quick 5 mile run today with no issues. The glass bowl is handy for seeing the fuel level. When I had the problem the level was only 25% up the glass. It's usually at 80%. If it happens again it might also be an idea to slacken the screw clamp on the glass for a moment and release the vapour - if I can reach it!

I will also make a kit up from the Moprod pump and the required tubing, wires etc. and carry it in the boot so I can fit it if I have to....

Cheers,
Dave.