Runs great when warm, rough when cold, thoughts?

[Healey Z]

1963 Austin Healey, L28 with round top SU's.

I have the motor dialed in and it is running great. When it is warmed up (160 degrees+) it accelerates wonderful, no stumble at steady speed, really a joy to drive. Now that it is cold, when the motor is below that 160 degree mark (perhaps 5-10 min of driving) it flutters on slow acceleration or steady speed.

The chokes are there and operable. The chokes help some when cold, but I think mostly because it raises the idle 1000 rpm. The motor is stripped of all the smog parts, intake warming tubes, air cleaner vents etc.

I know, I know...what do you expect?

The question is. Do you think the poor running when it is cold is due to the missing parts, perhaps wear in the carbs that expansion takes care of when it is warm or perhaps these motors just run a little rough when cold?

[Gary in NJ]

Do your carb's have the ports for coolant? These ports were added (in '72 and higher Hitachi's) to aid with warm-up and cold drivability. If you have the ports but aren't using them, consider putting them into service.

[Travel'n Man]

Great photo - I think you should post a few more! My L28 is a little rough until she warms u,p and then she is fantastic!

[FastWoman]

My L28 runs perfectly when stone cold in the dead of winter. As long as you have the right fuel/air mixture (richer when colder), it should run fine. Your engine probably wants more fuel than it's getting when it's cold. I don't know how that's achieved with a carb (mild choke?). I have EFI.

[olzed]

These engine need fuel when cold. The chokes are there to use when cold.

My stock 240 stumbles badly when cold, but is fine when warm. Takes six or eight minutes.

[Walter Moore]

When the engine is cold I have to keep the chokes on at idle or low speed operation. I have the heat tubes, but on the 71 they only heat the intake manifold. When the engine is dead cold they don't do anything anyway.

It runs a little rough until the temperature comes up, but then all cars from that era ran badly when cold.

BTW, when I say cold I mean below 40F. What does cold mean in Sacramento? That is a serious question, not a slam.

[LeonV]

Your engine is operating properly, use the cold start device when cold. If it runs great in the cold without the "choke" then you're running too rich.

[Healey Z]

Thanks for taking it easy on me. It sounds like it is running as good as I should expect. The intake does have the water passages blocked off and I will consider hooking them up. I drive the car regularly, including to work a few days a week. Cold here in Sacramento is low 40's.

[Jetaway]

Thanks for taking it easy on me. It sounds like it is running as good as I should expect. The intake does have the water passages blocked off and I will consider hooking them up. I drive the car regularly, including to work a few days a week. Cold here in Sacramento is low 40's.

I'm an hour south of you and while my 1972 sounds like it may run a bit smoother than yours when chilly, your symptoms don't seem out of line to me at all. I've bypassed the intake water passages, so that can't be the difference. Instead of going through the mess and bother of draining coolant to hook up what might very well be clogged passages anyway (mine were) why not try using the heat riser? $5.00 -- $6.00 for the flexible tube and no possibility of a drain **** snapping off or getting sticky cold liquid on hands or shoes.

Chris