Foam comes from over pumping. For most of my keg beers I (with a CO2 tank) use about 11-15psi). For a hand pump this is more difficult. You will have to resist the urge to over pump. If you are a little more engineer-minded you can look at THIS article to gauge more consistently your tap pressures. Make sure you let the keg settle after moving as well. Just like shaking a soda can, a lot of jarring will make the CO2 come out of solution.
A trick I use on my homebrew system (I use 5 gallon kegs) is gently placing the keg on its side and slowly rolling it about 3 feet forward and then 3 feet back. Then, I place it back in the fridge and repeat 3 times throughout the day. This helps the CO2 re-dissolve into the beer. However, if you are pulling the keg out of a trunk, throwing it in a trash can and packing it with ice...this solution isn't viable. In which case you want to let it settle and resist the urge to over pump.