Phase II trial to study the effectiveness of bryostatin 1 and cisplatin in treating patients who have metastatic or unresectable stomach cancer. Drugs used in chemotherapy use different ways to stop tumor cells from dividing so they stop growing or die. Bryostatin 1 may increase the effectiveness of cisplatin by making tumor cells more sensitive to the drug. Combining cisplatin with bryostatin 1 may kill more tumor cells.