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TR4/4A Stumble Off Idle When Hot

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Geo Hahn

Geo Hahn

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My TR4 (ZS carbs, stock everything) does fine on hot days except when I have to sit through a long stoplight. Then it wants to stumble a bit when first coming off idle.

This occurs in 100°+ heat and only after the car has been driven long enough that everything under the bonnet is thoroughly heat-soaked.

If I can anticipate the stoplight change and blip the throttle a bit it will not stumble but if I simply take off as usual it will sputter for a few seconds.

Am I correct in suspecting that a heat shield for the carbs may improve this?

Not driving in 100° weather would mean not driving at all, so that isn't really an option here.
 
I suspect so as well. Worth a try anyway, it certainly made my TR3 a whole lot happier in even 90+ heat. You could also try leaning out the mixture just a tad and see what that does.

 
I seem to have helped my problem in this area by wrapping the float chambers in foil covered bubble wrap (I don't know what the official term for this material is). I say seems because it could be the placebo effect, however I've not had a "vapor lock" symptom since.
 
Makes sense to me. Anything to help keep the carbs cool.
 
It does sound like the fuel in the float chambers of the ZS carbs is percolating.
I had this problem on hot days..not at stop lights because there is only one, but difficulty in restarting the hot engine after a good long run on hot days.
The ARE heat shield is easy to install, but it got so hot it created it's own problem.
I ended up putting a couple layers of heat shield insulation on the floor of the ARE heat shield and that was that.
 
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