Originally posted by Big Jim:
The hole in the copper pipe needs to be enlarged to overcome the cold stalling, especially in colder weather. Some actually have two plugs, one for cold weather and one for warmer weather.

The plug should have no impact on fuel use. I suspect that there are other factors, probably seasonal adjusted fuel blend.



Also colder conditions requiring longer periods of rich mixture for engine warm up, and perhaps different driving habits after initial install of the cap - i.e. testing to see if performance is hampered.

Must be that jumbly-wumbly thing happening again.