Heat riser on Packard 356 engine

[Guest]

The heat riser sping on my 47 Packard Super Clipper is missing but the riser itself is free and of course flops open. I am wondering what the engine running characteristics should be without riser closing when the engine is cold. I notice that on start up the engine stumbles and smokes excessively as though running rich until for about 3-5 minutes and then settles into a smooth idle . Is this what would be expected with a non functioning heat riser?

[Guest JT]

Yep, without the help of the exhaust gases (diverted by the heat riser) heating up the hot spot on the intake the fuel will not vaporize as well when cold and the engine runs rich. Running rich also doesn't help with the cylinder wall lubrication so it's worth spending the time to replace the spring.

[Guest]

Thanks JT. That probably explains the blowby gas coming from the breather as well,I suppose, if gas is getting into the oil and then is vaporized as the engine heats up. I'll get a spring ordered right away.