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N/A Idle Jets


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I'm having some problems with the persistent acceleration stumble between 2000- 3000rpm and thinking that although they're clear and the carbs have been rebuilt in the last couple of years, the original jets might have gummed up a bit over 20 odd years. I've read here that because the jets are on the limit of what's required due to emissions control, even a small restriction can cause a problem. I've also seen here that a few folks have had success going to a slightly larger jet.

I'm on DHLA 45s and (from DeRoure) it looks like standard idle jets for an N/A car are 56. Is it worth going up a size or two (the Turbo uses 58) or just getting new 56s?

Edited by eeyoreish

Not worth starting anything now...🍺

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I'd have thought you'd be running on the main jets once the RPM rises over 1,500.

Are the carbs perfectly balanced & the idle mixtures correctly set wih something like a Colortune:thumbup:

Cheers,

John W

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I think they're a touch out of balance just now but the stumble is still there when they've been balanced. Having driven it to Goodwood today the stumble is probably a bit lower than I guestimated when I was posting. If I keep the revs up above 2000 between changes it's fine so I'm pretty sure it's on the changeover from idle to mains.

Not worth starting anything now...🍺

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I followed the manual recently to get the mixture better, closed the screws down gently then 6 half turns open again. I kept a note of how many turns each screw took to close just in case I needed to put it back as it was.

I have the same engine setup as yourself and I feel it made a difference once I'd set the revs at idle to just below 1.

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I'm 6 half turns out now but the air flows do need balancing again. It seems like there's a knife edge of getting it right and being even slightly off the perfect settings results in this stumble. Hence I was wondering if slightly larger jets would help.

Not worth starting anything now...🍺

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The method in the manual is just a starting point for carbs & engine in perfect condition.

If you're not using something, like a Colortune, to correctly set the mixture then you're just guessing.

Good luck. 😕

Cheers,

John W

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Better renew all jets, even it looks little suspiciously . You can also change idle jets to 58. not really necessary but better for cold starts.

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  • 2 weeks later...

You can easily whip the jets out and have a quick look to see if they are cruddy. Mine were, and I cleaned them by running a load of carb cleaner through them and into the jet housings - It did make a difference (mines a turbo)... I had a pretty fierce hesitation/stumble from 3000+ rpm

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