[Shiny]

Originally Posted by dataway

Is the problem of evaporation any worse with the later carbs with the larger vent tube than the early ones with the smaller tube?

If you think of the carb as a jar with a hole in the lid, then yes, all other things being equal, the bigger hole will allow a higher rate of vapor loss.

But that "all other things being equal" thing makes it pretty complicated. Gas evaporation happens. How fast it happens depends on both the "drivers" (temperature, composition/vapor pressure, surface area, concentration of vapor in the air outside the vent, etc.) and the "limiters" (concentration gradient, geometry, etc.).

So my guess is GM knew the answer to this question, but IMO other differences in the carb designs, engine designs, operating temperatures, etc. would make it VERY difficult to confidently say it's practically worse with the later carbs.

Just for grins, my car hasn't been started in a few months so I'm going to measure the time it takes to start. I expect the bowl to be empty from evaporation. I normally just pour some gas down the vent but I really don't know how long it will take to fill the carb just by cranking.

I do know it takes so long I want a primer pump. My tolerance may be different than others, though. 5 seconds cranking may seem OK to some, may feel like forever to others...

I plan to let it warm up, then shut it off and measure the carb temperature as it cools. I'll try to monitor the fuel loss inside the carb, but not yet sure how to do this.... any ideas (I won't open it up for this)? Maybe a dip stick down the vent?

Mike