Dellorto Idling Frustration - S4 Elan

[William2]

I still can't seem to get the DHLA40E carbs to idle reliably. I start the car from cold using the choke briefly (as is normally necessary with Dellortos) and it starts easily and will idle below 1000rpm initially. As soon as you take the car for a drive the idle becomes erratic an starts to kick in at about 1300/1400 rpm but sometimes if you wait a while it may start to come down. I have tried blipping the throttle at standstill but this has no real effect. Apart from the idling the carbs are working well and the car accelerates with no hesitation. I have also removed the plugs several times and they are the correct colour.
I have stripped the carbs twice and rebuilt them with new jets and gaskets, etc and checked that the butterflies were closing. Today I removed the airbox cover and double checked the carb balance using a synchrometer. All chokes gave the same reading.
The throttle cable is new and correctly adjusted to give a small amount of free movement and I have driven the car briefly with the bonnet up. I have also tried removing the headlight and servo vacuum pipes from the manifold and plugging the holes but to no avail.
Could the problem be within the carb itself? Is it possible for the choke facility to stick or the idle jets and adjusters be the culprit.
I am trying to avoid taking the carbs off the manifold unless really necessary.

[alan.barker]

Imho never use the chokes on Dellorto carbs to start. 2 or 3 pumps like Weber.
To balance it's easier with a Carbtune.
Alan

[LaikaTheDog]

i had a similar problem with my previous big valve on dellortos.
i took it to a specialist rolling toad and it turned out that i had a twisted spindle.
it meant that i could never get a reliable idle... the butterflies never sealed properly

[Robbie693]

Watching with interest - mine has started to do this too recently...

I have noticed that the idle is more like it should be with the headlights on and the fan running, - more load on the alternator presumably.

[bitsobrits]

Okay, this is going to sound off the wall... Take the car for a test drive with the bonnet removed and see if the problem persists.

On RHD Elans, the short throttle cable routing can be such that depending on whether the cable is forced forwards or backwards by closing the bonnet the idle speed can increase once the car has been driven and the cable has shifted. The solution is to set up the car with the shortest cable run consistent with allowing a proper arc for full actuation, and to ensure just a wee bit of slack when the bonnet is fitted.

This issue can occur with Webers or Dellortos running a slightly over long cable.

Of course there are other possibilities, like something causing a vacuum leak when the car gets warm, such as leaking mounts (O-Rings).

[Orsom Weels]

It is possible the choke, or starter valve as Dellorto refer to it, is not completely sealing the fuel off when closed, which will result in fuel bypassing the butterflies & idle system, & therefore effect the idle speed. Another possibility as mentioned above is an air leak at the inlet mountings, a bad O ring or broken/badly adjusted thackery washer can cause an air leak when the butterflies are closed & vacuum is at it's maximum, again this can effect the idle speed. With regard to using choke/not using choke for cold starting, everybody has their own opinion of what's best, but on some Dellorto's, the accelerator pump jets squirt straight down into the venturi, not into the inlet tract & with this type jet, if you pump the throttles without the engine running/sucking, you can get a build up of fuel in the carb venturi which can be a problem if you get a back fire. I have always found full choke & don't touch the throttle until it fires up works fine on Dellorto's.

Tim

[nigelrbfurness]

All my Elans have suffered from this problem at one time or another, Steve's diagnosis is most likely the correct one from your description of the symptoms. A quick way to check it is to move the throttle cable by hand, lightly with a finger, to a position roughly where it will be forced to be when the bonnet is closed (with the engine running, of course). You can also check how free the linkage is to rotate at the same time. It is a matter of adjusting the free play in the cable carefully and also you can polish the bit of the throttle linkage that receives the cable outer and rotates in the throttle lever. A bit of light oil here helps as well. I have also seen people fit an additional return spring. A stronger standard-type return spring can be used too. Once you have established a correct idle with the cable in the right place, look for a way to hold it there - a cable tie fitted loosely perhaps.

Nigel F.

[William2]

I have new Misab rubber O ring plates tightened to the recommended amount so I am hopeful that the problem isn't an air leak. I have not yet tried running the car without the bonnet on so will give it a go to rule it out.
The only other thing that occurred to me is I believe there is an air balance adjustment between the carb throats. I wonder if that may be the problem. I will also examine the choke mechanism. Thanks for all the help so far.

[rgh0]

Have you checked the location of the butterflys at idle versus the progression holes to make sure none of the holes are exposed ?

cheers
Rohan

[William2]

Hi Rohan, I guess my intention was to eliminate every other possibility before having to remove the carbs themselves. I am pretty sure I checked that the butterflies were covering all the progression holes when I stripped the carbs but I will heed your advice and double check this and make sure the spindle isn't twisted.

[rgh0]

That lazy return to idle if not due to a sticking shaft or throttle cable is almost always due to a partially uncovered progression hole. You can check by removing the plug above the holes without removing the carbs

cheers
Rohan

[elanner]

I read somewhere in this forum that a good way to check for O ring leaks is to pour water (a small amount, presumably) onto the rubber mounts while the engine is running. If there's a vacuum leak the water will get sucked in and alter the idle.

I've never done this myself although I keep meaning to. It seems like a clever idea, perhaps somebody can confirm that it works?

Nick

[mbell]

I've had this on my car too, never figured out the cause. For me happens with and with out bonnet on, happens with new weber carbs, I am pretty certain it's not an air leak. It will lower the idle if you manually close the throttle plates a fraction.

My guesses for my car would be not a strong enough return spring, carb balance adjustment mech is slightly opening one carb, dizzy advance mech is sticking. I've bought the standard return spring and cleaned/lubricated my dizzy so I am hoping when I refit the engine this will magically be addressed.....

[alan.barker]

The Dizzy can be checked with a strobe and opening and closing throttle
Alan

[William2]

Still trying to resolve the high idle speed problem. I tried spraying WD40 around the Misab O rings but this didn't suggest there were any air leaks. Had a long chat with Miles Wilkins the other day about it. He suggested I try adjusting the floats to 16.5mm instead of 14.5 to see if that made any difference so that's next on my ever decreasing list!!