I had the same problem with my Mercury's only mine wouldn't hold fuel at idle. Every time I throttled up after a drift or prolonged idling the port engine wouldn't power up. A pair of factory Mercury bulbs and the problem was fixed. When I removed the the Tempo bulbs (I only had two trips on them) the check valves wouldn't even keep the fuel from draining out the "in" side.
If you would like to file a complant, here is their web site;
www.tempoproducts.com
I did.