TR4/4A Stumble Off Idle When Hot

[Geo Hahn]

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.

 

[TR3driver]

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.

 

[Crankshaft]

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.

 

[TR3driver]

Makes sense to me. Anything to help keep the carbs cool.

 

[poolboy]

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.