Lotus Elan

Sticky throttle

PostPost by: greg.harvey » Sun Jan 14, 2007 11:15 am

Hi all,

I finally got my +2S back from a local classic car mechanic (guy turned out to be "steady" at best - he had it seven months!!) and it was all polished up and running sweetly. I drove it 20 miles, decided to nip on to the motorway to open her up a little, put my foot FLAT to the floor on the sliproad and when I was rolling went to change in to 5th and **Vrrroooommm** - throttle stuck open!!

Girlfriend had had similar issues with an old Fiat Uno told me to pull the pedal back with my toe, which worked (thankfully!! stuck on the motorway with a wide open throttle is pretty hellish!)

So, limped home carefully, pulling the pedal back after each acceleration - once I got back to the garage, I did a little experimenting - seems it does return (slowly!) on its own if you leave it, so my guess is it's shed a spring somewhere. I'm loath to return it to the mechanic who kept it for seven months, so I'm going to try and sort this myself.

I dug around and found this thread, which has given me some ideas:
http://www.lotuselan.net/forums/viewtopic.php?t=2238

I'll pop out and look later, but here is my summary - is there anything I've missed in my checklist?

- Seems there is a balance screw between the two carbs (twin Delortos in this case) - could've slipped somehow? I guess not, but don't know how the mechanism works.

- Could simply be bad luck/timing and the cable's knackered? (I don't think it's this as it happened too suddenly...)

- Maybe one carb has shed a return spring and the one on the other carb isn't quite strong enough to return both butterflies?

- Or perhaps when I over-vigorously applied the throttle I actually dislodged the return spring on the pedal?!

Anything else?

Cheers,

G
Greg
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Epping, Essex, UK

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PostPost by: lotuselan2 » Sun Jan 14, 2007 5:32 pm

Greg
Do not count on the internal return springs in the carbs. They are only strong enough to close the carbs and not pull back the throttle cable. Between the carbs there should be an external return spring. One end is attached to the throttle lever near where the cable is attached. The other end is often fixed to the air box in a little hole that has a brass ring. You may or may not have an airbox. My Delortos have a nice home made two-legged tripod (must be a bipod) mounted between the two carbs with a hole for the other end of the spring.

The spring can be found in a hardware store but select wisely as the spring extension can be about 100%. Mine is about 1/4" diameter and has a good 1 1/4" or more of length when at rest. Spring should extend easily by hand; you don't want a door closing spring!

Also look for your cable binding at one end or the other or crimped in the middle. Cable should be well oiled with liquid moly. Disconnect cable from carbs and be sure if moves freely. This is the most common problem.

Let us know what you find.
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PostPost by: nhhiker » Sun Jan 14, 2007 7:26 pm

Just one more thing to check. See if the pedal moves freely by itself. If you are pulling the pedal back, the cable may not move if is stuck at the carb but will return if it is the pedal. The +2 I just got, had the pedal needing lube on the pedal/brake shaft. That was my problem. The biggest problem there is get the oil up to the shaft.

Bill
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PostPost by: rgh0 » Mon Jan 15, 2007 8:51 am

Greg

Unlike Webers, Dellortos have a much more substantial return spring incorporated in the carbs. They are external at the rear of the carbs between the barrels. Check that they are properly in place. The Weber internal return spring is much weaker and cannot be seen.

The standard Lotus installation also had a hairpin style spring between the Carbs. It connected between an arm on the intake back plate below the carbs where the end of the cable inner connects and the central arm on the carb shaft where the cable outer connects.

There is also a stop adjuster on the back of the accelerator pedal this should be set so that it hits the firewall when the carbs just reach fully open to avoid overstressing the cable and carb levers / shafts. This can distort the system and create return problems

The balance adjuster is a screw and spring loaded plunger arrangement on this lever arm between the carbs and is unlikely to be the source of your problem

If the three springs are in place and the pedal and cable and carb butterfly shafts are all moving freely and properly adjusted then you should have no problems. If anything is binding in the system then it may jam and cause it to take a while for the carb to close.

If you dont have the Lotus standard setup ( eg tension spring replacing the centre hairpin spring etc ) then whether it works or not depends on how well its been designed and installed

cheers
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PostPost by: greg.harvey » Tue Feb 20, 2007 5:59 pm

Well, I fixed this myself in the end - closer inspection (when I got around to it) revealed the throttle cable looks nearly new (was probably fitted just before I bought it, four years ago - it's still shiny - I don't do many miles), however the return spring (the torsion spring at the end of the cable) is positively ancient!

When I put my foot flat to the floor, I sheered off half of the hook which holds the return spring in place at the end of the throttle cable. The spring was just dangling there! Fortunately there was enough of a hook left to bind it back in place with some garden wire, which ought to hold while I source a replacement.

Throttle "springyness" returned to normal! :-)

Cheers,

G
Greg
+2S 130/5 Elan <== FOR SALE! PM me if you're interested...
Epping, Essex, UK

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