Lotus Elan

Dellorto idle speed too high.

PostPost by: elansprint71 » Fri Jun 05, 2015 7:13 pm

Can't find an answer in the archives!

I have recently had my 40 DHLAs rebuilt and refurbished and they now look like new. I had new jets fitted to the spec in the Lotus manual (as a starting point). Dynamic timing set, new plugs, leads, dizzy cap, coil. Lumentition Optronic ignition.

I am going thro' the adjustment of the idle mixtures screws using the combined wisdom of The 'shop manual, Miles Wilkins TC book and Des Hamill's Dellorto book. My problem is that the idle speed is between 1200 and 1500 rpm. The lever is not touching the throttle stop screw, the throttle cable is not pulled tight so I'm stumped as to what is wrong.

If I apply pressure to the throttle lever, it is possible to slightly move the spindle and close the butterflies ever so slightly and decrease the tick-over a bit; however the combined springs do seem to be returning the spindle to their stop position, my applying pressure kind of feels like I'm forcing it a bit beyond. I've made sure that that one carb is not holding the other open by unscrewing the linkage adjuster.

Any ideas chaps? Am I missing the blindingly obvious?

Apart from this the motor seems to pull strongly, a very slight hesitation on opening the throttle sometimes but it is only slight. I've got a Gunson carb balancer and a couple of Colour Tunes, problem is I'm off to France for 3 weeks on Monday (not in the Elan!) so I will probably have to sort it out when we return..
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PostPost by: billwill » Fri Jun 05, 2015 7:35 pm

I would guess that your idle-bypass screws are open.


Hold on, I'll find a link to how I set up my Dellortos.. ......

OK, this message is where I described setting the idle-bypass screws.

lotus-elan-f19/getting-ogu-roadworthy-again-t26101-105.html#p191111
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PostPost by: elansprint71 » Sat Jun 06, 2015 1:07 pm

Thanks Bill; my Dellortos do not have do not have idle bypass circuitry, there are no screws to screw with!

After doing a lot of reading and a bit of adjusting of the idle mixture screws I have managed to get the idle speed set to the correct rpm; however the plot thickens: I attempted to balance the carbs using the Gunson meter and can get no reading at all on cylinder 2! I can balance cyl 1 against 3 & 4 but nothing doing with cyl 2.

Somewhere in my garage is a four-branch manometer but can I find the bugger?

I've learned that the idle mixture screws are used for more than setting the idle mixture and are very important during the progression phase. Looks like the Des Hammill book will be coming on holiday with me.
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PostPost by: billwill » Sat Jun 06, 2015 9:11 pm

Oh, I thought all the Dellortos had the screws, but none of the Webers.
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PostPost by: oldchieft » Sun Jun 07, 2015 11:29 am

Have the throttle discs been centred correctly?

I would slacken the screws in the shafts and operate the shafts to centre them, it means getting the carbs off again.

When it is right the disc should trap the thinest feeler gauge you have, and it should be the same in both barrels.

When you put them back, have the stop screws slackened back, connect the linkage and it should still trap the feeler.

Screw in the stop screw till the feller comes free.

Then do the same to the other carb at the linking screw, that should be a starting point before you fire up the engine.

Jon the Chief
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PostPost by: elansprint71 » Sun Jun 07, 2015 6:08 pm

@ Bill; seems that both makes do, or don't, according to Des Hammill.

@ Jon, I gave them a good eye-balling when they came back and shone a light through to look at butterfly vs hole. They looked completely closed but I'll investigate when we get back from France.

Car is running really well too! :?

Keep the suggestions coming folks! :D

Thanks.
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PostPost by: Galwaylotus » Mon Jun 08, 2015 2:45 pm

Vacuum leak or too much idle advance .
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