Both oil pumps? The one in the case (the return pump) and the one in the small housing that covers that (the feed pump)?
Does it have the OEM oil pump cover on it with the safety tab sticking out on the inside at the center? If it has a Ready Racing cover (identified by an "R" on a black cover, you can install the oil filter backward and block off oil feed to the engine past that point.
If the feed pump is OK, then you need to verify that the oil passages are clear by pushing oil through them from one end to the other. Get an old gear lube bottle, or any other plastic bottle with one of the conical "squirt" tops on it, fill it with oil, and force it though the oil passages at the pump cover flange. Review the oil diagrams in the manual.
Another possibility is that the return doesn't work, so when you fill the crankcase with oil, it never gets moved to the oil reservoir in the front of the engine so that it can reach the feed pump.