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Sudden drop of idle speed in my Dart

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John-B
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Sudden drop of idle speed in my Dart

Post by John-B »

Has anyone else noticed a sudden change in idle speed recently?

My Dart used to idle at 600 to 700 rpm for years until last weekend when it started idling at less than 500 rpm and creeping down to 200 when it stalled.

I'm wondering if it could be caused by a change of fuel to 97 octane E5 super petrol compared to 95 octane previously. I'm surprised that it would make a difference.

It's easy to adjust the idle mixture screws but I like to know the reason why something unexpected has happened. I had to turn the screws about 1.5 turns which was a lot more than I expected. The engine still runs evenly and I haven't done anything to the engine for seven years since it was reconditioned. I thought it might be caused by the carb floats getting pinholes and sinking but there's no overflow.

I suppose I might need to adjust the main mixture or the timing, but as the car runs well I don't want to change anything yet.

Any ideas?

mikemillen
Posts: 307
Joined: Mon May 03, 2021 8:34 am
Location: Bognor Regis

Re: Sudden drop of idle speed in my Dart

Post by mikemillen »

Just an idea... before you touch anything else, just make sure that the nuts holding the carburettor(s) are still all tight and not allowing an air leak.
Likewise the inlet manifold nuts.

Ian Slade
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Joined: Sat Feb 13, 2016 9:54 am
Location: Sevilla Spain

Re: Sudden drop of idle speed in my Dart

Post by Ian Slade »

Perhaps it got tired of idling at 600 -700rpm, the idle speed should be 400-500 rpm, it's an 8 cylinder engine 600 to 700 rpm is equal to 1200 to 1400 rpm on a 4 cylinder engine, way over the top :)
Owner since the 70's, Genghis is slightly to my left.

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