Not likely to be an ignition problem.
I have found that having the jets adjusted slightly too rich results in
an idle that is smooth when cool but gets progressively rougher as the
engine gets hotter. Lean the jets a couple of flats.
It also seems that there can a great variation of carb temperatures at
idle, depending on air intake temperature & fan flow. A cold air intake
& a high flow fan reduce temperatures regardless of heat shields or
insulator spacers. I've never experienced fuel boiling in the float
chambers even with no insulators or heat shield. My H6 carbs have
Neoprene grommets between the carb bodies & float chambers which may
help. The HD carb has a completely different float bowl attachment which
doesn't provide as much heat insulation. Possibly my tube header also
causes less heat to the carbs.
As Greg says, a faster idle helps, maybe partially due to more fan
cooling of the carbs.
Just rambling about carb heat in general. If it takes shields,
insulators & whatever to make it better than that is obviously what is
needed. Try the faster idle & leaning the jets first.
Greg Lemon wrote:
> When I used to run SU carb cars with lucas electrics year round in Nebraska,
> where is gets very hot in the summer, I would turn the idle up a bit in the
> summer, because when the car (any of them that I owned over the years) got
> really hot idle would fall off and it would run rougher.
> Maybe simplistic and a patch rather than a cure, but it worked for me.
> Greg Lemon
> 54 BN1
> ----- Original Message -----
> From: "John Peak" <firstname.lastname@example.org>
> To: "Healey List" <email@example.com>
> Sent: Tuesday, June 29, 2004 6:01 AM
> Subject: Poor idle when hot
>>Perhaps some of you can help me diagnose a problem. My BN7 (HD6 carbs)
> runs great and idles smoothly until hot. By hot I mean like after driving
> for half an hour in 90 degree temps (I live in south Florida). It then
> becomes unable to sustain an idle. It just idles rougher and slower until
> it dies. I suspect an ignition problem although all components were
> replaced within the last 18 months. Any suggestions as to likely culprits?