Lotus Elan

Thirsty +2s130/5

PostPost by: Paul Steer » Tue Jul 20, 2004 10:49 pm

Hi,

I am running a 73 +2S130/5 as an every day car, the best I can get is 17mpg ,on
leaded !! I am having to hide the fuel bills from my wife. The car has dellortos and I have given them a short service. The jet numbers seem correct. The float levels are at 16mm. I have checked for leaks but not found any. The timing & points are OK. The car starts well without choke(I am told this is normal). The temp guage takes a while to get to 85 but once there levels out with the aid of the electric fan.
An oil cooler has been fitted. I was interested in the evaporation comments & will look into it. The car does have a bit of a petrol smell to it but not that bad. If I drive slightly more aggressively I get 12mpg at 117p per litre this is no joke. Otherwise performance is excellent , I just dare not use it. What mpg should I expect. I have been told I can use Shell Optimax unleaded without any worries of valve seat regression , but have not as yet as I wanted to get it right on leaded first. Any advice gratefully accepted
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PostPost by: rgh0 » Tue Jul 20, 2004 11:53 pm

Paul

Your fuel consumption does sound a little excessive. In my 73 +2 130/5 I get around 18 mpg when driven very hard on the road and around 25 mpg when driven in normal traffic. It depends on what you consider normal traffic and hard driving I guess but even so I would not expect to get down to 12 mpg except on a race track. ( I get around 5 to 8 mpg in my Elan on the track !)

My plus 2 has the standard Dellorto jetting and is otherwise standard apart from lumenition and runs much the same as you describe yours. I use Shell Optimax or its equivalent from BP or Mobil here in Australia.

Possible items to check

1. Fuel evaporation, plug up the 2 vent hoses from the tank, leaving a much smaller breather hole in the plugs you fit.

2. Fuel leakage out the filler is a common problem, especially if you fill the tank right up.

3. Any other fuel leakage points between the tank and carbs. if running the mechanical pump check for leakage from the pump. If the diaphram splits it can leak into the sump where the petrol then evaporates off and you cant see the leak.

4. Ensure the choke levers are fully closing off or the carbs.

5. Check for blockages in the intake air side filter or ducting, restricting air flow.


If all the above is OK and ignition timing and cam timing are OK then a trip to a dyno to get the carbs tuned better is probably needed to get the best economy you can.

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PostPost by: john.p.clegg » Wed Jul 21, 2004 6:17 am

Mine averages 29 mpg
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PostPost by: kevin » Wed Jul 21, 2004 1:55 pm

Paul

I'm not sure that I can solve your problem, but here's my experience. It at least will give you something to compare with.

From may +2 (standard twincam 'S' - 4speed) I'm getting 22-24mpg. The car is used daily to and from work - approx 5 miles each way in heavy traffic. As well as this I use it for pleasure - but not as economically as I perhaps ought!

I have been using Shell Optimax for the last few fill-ups. Before this I used supermarket fuel + castrol valvemaster where I was getting 18-22mpg. However the engine is newly rebuilt so I can't attribute the improved mpg to Optimax as it's presumably loosening up all the time. The engineer who rebuilt my head just re-cut the seats and fitted new valves. He was adamant that the seats were perfectly acceptable for unleaded.

I always notice spillage from the petrol cap after filling up the tank but I can't say how much fuel I am loosing here. The tank breather system is modified, so that it vents back into the filler neck rather than to the atmosphere. I'm not sure if this is why I get the leak as I never drove the car before the mod.

I serviced the Webers at the same time as the engine re-build - completely stripped them down. Repaced main and idle jets as they were blocked. Thoroughly washed out the bodies (twice - but thats a long story). I setup the carbs using a CO meter to approx 3.7%. The plugs are currently slightly blacker than they should be, but I get popping / backfiring through the exhaust on runoff. No.4 plug was lighter than the other 3 so i've have to richen this by unscrewing the mixture screw slightly more than the others.

Like you I have an electric fan fitted that I only comes on if standing in traffic for a while on a hot day. The engine heats up to normal within a couple of miles of starting. The mechanical fan has been removed and the radiator has a thicker core than originally.

I don't currently have an oil cooler fitted. There was ione on when teh car came to me, but for one reason or another I have not got round to re-fitting as yet

G
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PostPost by: Hamish Coutts » Wed Jul 21, 2004 8:36 pm

Paul,

I agree with Rohan. I had fuel consumption problems, though not as bad as yours. Mine was caused by a ruptured rubber diaphram in the mechanical pump - the fuel was dripping out of a small drain hole in the bottom of the pump. This only happened when the engine was running so I didn't notice the problem until I was standing outside the car adjusting the tickover setting. Had a lot of trouble finding a new pump so went fo an electronic one - a Facet from Demon Tweaks. Consumption a lot better now.

Best of luck,

Hamish.
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PostPost by: DaveExcel » Thu Aug 19, 2004 8:24 pm

Have you had the carb's balanced, not sure if this would be all the problem but it might not be helping.
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PostPost by: worzel » Fri Aug 20, 2004 10:04 am

Hi

Hate to say this but in my experience (26 years ownership) big valve engines tend not to be economical. I used to use my Sprint as an everyday car for about 11 years and found it was markedly less economical than the bog standard S4 I had before it. The S4 was very low mileage and averaged around 35 plus in town driving (quite trus I assure you) but the Sprint using exactly the same driving style would only stagger to about 22 mpg in town and just under 30 on a run. The Plus 2 130 I had averaged about 18 mpg in town (again same driving style) and on a run about the same as the Sprint.

In contrast, and using the same driving style the Excel I run as an every day car is better than both on a run but averages about 19 mpg in town.

John
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PostPost by: type26owner » Fri Aug 20, 2004 6:48 pm

Paul,
I don't have any direct experience with Dellortos but if they are identical to the Weber then I might be able to point you to a potential problem. If the float valves are leaking or the fuel level in the float bowl is set too high then the fuel could be literally pouring down the passageways leading to the auxiliary venturis. On the weber one can remove the inspection cover from over the main jets and actually remove the emulsion tube while the engine is idling and with a flashlight peer down into the 'well' and see if there is a problem. The passageway is an 6mm diameter opening on one side of the well about 20mm down. A pipette is also a trick way to accurately measure the level. Black smoke billowing out the tailpipe is the dead giveaway.

Don't drive the car if this problem exists. The fuel just trickles down the wall of the induction system and most does not get evaporated so it will not burn. By staying as fuel globules in the combustion chamber it just gets swept out with the exhausting gas. However some of it will wet onto the cylinder walls and will wash off the oil film that keeps the rings from wearing the cylinder oversized in diameter wearing out the engine. THIS CAN HAPPEN QUICKLY. The rest makes it by the rings and ends up in the crankcase where it dilutes the engine oil. The oil viscosity is reduced and this can cause the destruction of the oil fed bearings. Fresh oil will turn black in a few hunderd miles.
-Keith
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PostPost by: JJDraper » Sun Oct 17, 2004 7:14 pm

:o Something must be amiss in the go juice department! My +2 has a big valve head, with QED 360 cams, with Webers, big jets & chokes is has never fallen below 24, and usually returns around 27-29, with 35 available on a long run and a light foot. My best figure was 39 on a trip to Brugge (Belgium) from Milton Keynes, when I went touring. I am quite obsessive about recording MPG (tank, moving average, monthly etc - aren't spreadsheets wonderful?) so these figures are accurate and not due to the odd faulty pump readings...

As I have hardened valve seats, I usually use standard unleaded, unless it is very warm & I intend a little extra fun ;), when I use Optimax. You can tell the difference on full song.

Try tuning the car with a Gunsons Colourtune, so you can see what is going on. Another thought, are the brakes (including the handbrake) dragging?
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PostPost by: cdraper » Tue Oct 19, 2004 5:40 pm

I found on the big valve it worked much better with 30mm chokes than with 33mm and I could drop the main jets a coupls of sizes. Weber agent said I would lose about 3-5 bhp above 6500rpm - so what. Fuel consumption really improved togeather with revised tank venting.
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