Ice cold carburetors

Hey guys, I have a 79 Kz400 and I fabricated a stainless 2 into 1 intake and used a mikuni vm32 carb. It starts and idles great howerver after idling for a couple minutes the intake and carb get frosty cold. The ambient temperature doesn't seem to matter, happens on a cool 50 day and a hot 85 day. The bike is rideable but bogs when the throttle is snapped open or under WOT. It seems to be running rich or dripping gas into the engine with white smoke that smells like gas coming out of the exhaust when warming up. I then switched to the stock carbs and it ran okay but even those get ice cold as well. Does anyone know if this is normal or had a similar experience? Thanks

I think what your experiencing is called " latent heat of evaporation". The evaporating fuel causes the temperature to drop . Usually the carb is too close to the engine to cool down that much.

The atmospheric air gets rapidly decompressed when it enters the vacuum of the intake. That causes rapid cooling. But on an 85 degree day, the carb(s) should eventually heat up. For cold weather riding, some people put shrouds on to get engine heat to warm the carb.

Thanks for the input guys! Im going to do some research and play around with intake design to see if I can get this figured out

While taking flight training we learned that an average carb will cool the air about 30 deg F while in operation. So on a standard day of 59 Deg F the carbs would actually ice up with the 30 deg drop. It's caused by the Bernouli principal inside the carb, which is needed to suck gas out of the bowl. The air is compressed on the intake side of the carb, then forced through the venturi of the carb throat, then rapidly expanded in the in intake manifold. Now your motorcycle usually won't be a problem because the carbs are very close to the cylinders, All carbs do this but usually we don't go putting our hand on the carb bodies while riding to notice it.
Long story short unless the carb actually ices up and stops working it's not a problem and completely normal.

Single carb feeding two, as the factory had two 36mm carbs, depending on year, your using one. Did you use the factory carbs with dual or your one into two manifold? Seems to me, running a single carb with dual manifold you should have at least twice the size carb for your engine, you feeding 2 cylinders with one carb now. Twice the vacuum through a carb originally designed for that bike running on one carb, shouldnt work properly. You should be running two 36mm carbs not one, or one carb with at least the same capacity as two. Drawing much more air through one carb may be causing much of your problem of icing, or carb getting colder than ambient air temp. More air velocity through a single carb, try both carbs, with factory manifolds, rebuild stock carbs, then see what happens.

It doesn't need a carb twice as big as stock since it is still only feeding 1 cylinder at a time. However, it is feeding the engine twice as often as a 2-carb setup, so there is twice the air/fuel flow over a given amount of time/rpm, and that could be contributing to the icing. Ed

Correct, Carb size as fuel requirements, no, but amount of air has doubled, because now 2 cylinders using same carb, fuel consumption and operation has now has doubled, causing icing problems. Possible larger manifold runners to reduce velocity may help.

You have to make a careful distinction between "average", and "instantaneous", when you are dealing with pulses.
If you connect a 5" hg, average, vacuum source to another 5" hg, average, vacuum source, the total vacuum is still 5".

The average amount of air flow has doubled through the carb, but not the instantaneous amount of air flow, because the pulses are perfectly offset on a 360 motor. The instantaneous vacuum peak does not double. Whether the average goes up or down is dependent on volume and RPM etc.

In practice, as it's been done many times, people find the carb size does not need to increase much, if at all, and report troubles if the single carb selected is much bigger than the original carbs.

also, to the OP, you are going to have to rejet the carb. the carb was jetted for a smaller cylinder as it has a smaller diameter than the stock one.
I would not be surprised if you have to drop the needle and raise the main jet size, but that is a wild ass guess.
dripping gas is obviously a big problem worth starting with.