Very high oscillating revs at temperature - Eclat

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Lotus-e-Clan
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Re: Very high oscillating revs at temperature - Eclat

Post by Lotus-e-Clan »

Come to think about it, surely there must be a few detailed videos on YouTube showing DHLA rebuilds, including the idle screw assembly.
I know Andy Jones on Shrigleytube has done a few but his videos are not well indexed so it's a job to find out which episodes show more detailed DHLA builds. Tonight's episode was just a quick reference to a rebuild, not detailed.
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Re: Very high oscillating revs at temperature - Eclat

Post by rbgosling »

barbicaneclat wrote:
Sun Jan 19, 2025 01:11
I'm not quite sure what you mean by the spring connecting to the airbox - if you mean the springs at the back of the carbs, those are present, and the throttle goes back with a good amount of force when released, so the spring there seems fine too. There is a very (very) small amount of slack on the throttle cable, yes, it needs to be moved a few mms before it straightens out and starts pulling.
Spring 004 in the picture below. It links between the throttle control and the underside of the airbox, to help pull the throttle closed. Well, it does on an Excel, to be honest I couldn't say for certain whether it's fitted to the Eclat. In any case, it sounds like you've checked and the throttle is closing properly, so that's probably not your problem.

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Re: Very high oscillating revs at temperature - Eclat

Post by barbicaneclat »

In good news, replacing the idle jet rubbers fixed the unpredictable problem. It did not, however, fix the problem of very high revs as soon as the accelerator is pressed. Turns out these were two separate issues.

I’ve found on examining further that the throttle plates are in fact much too far forward on both carbs. They are balanced between the two sides of each carb at least though. See pictures. This is at idle without any pressure on the throttle lever.

I presume I have to get these quite far back now. How do I do this without twisting the throttle plates further or breaking the whole throttle rod? Any advice appreciated…
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Lotus-e-Clan
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Re: Very high oscillating revs at temperature - Eclat

Post by Lotus-e-Clan »

If the linkage and cable between the carbs is not stopping return, and the throttle stop screw and or the throttle lever itself is not preventing return, then we are back to the centralisation of the butterfly plates within the barrel. Doesn't take much decentralisation to keep the throttle open. And it only has to be one plate catching.

When you had them off did you shine a light behind each plate to ensure no gaps?
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Re: Very high oscillating revs at temperature - Eclat

Post by barbicaneclat »

Throttle returns fine physically and seems to be in its proper resting position when at idle, so I think it must be the butterfly plates. I didn’t shine a light through and I stupidly took a spanner to the nuts on the side of the carbs at one point as they didn’t seem properly tightened. I imagine that might be why it’s now so far forward.

I’m wondering how to twist the whole thing back without messing up the relative position of the throttle plates at each side of the carb. Do I just put a spanner both sides and twist the nuts at the same time, with the throttle plate static, until the butterflies are behind the first hole?

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Lotus-e-Clan
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Re: Very high oscillating revs at temperature - Eclat

Post by Lotus-e-Clan »

I guess you should carefully loosen the spindle nuts to see if you have already twisted the spindle. Hopefully you've just caused the spindle bearings to bind, but if you put too much torque into the spindle, may have twisted the spindle. Either way you want those plates to close properly before you can resolve your issue.
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Re: Very high oscillating revs at temperature - Eclat

Post by MetBlue »

Do you have the book about building / power tuning the twin chokes? Around page 35 there's good info about refitting butterflies into the spindle. A photo shows the butterfly being held with long nose pliers whilst torque is applied to the spindle nut.
You've checked you have the butterfly's the right up in the spindle I assume.
What goes together.... Must come apart.

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