Have you checked to see if the choke butterfly is properly aligned? Most of my gas engines have been DA and 3W, I have seen issues with the clone Walbro carbs. I recently acquired a 3W 70 twin that had a Tillotson carb that even after a rebuild would not seal. I ordered a Walbro from DA because I know that DA only sells genuine Walbro that are built and inspected to Walbro standards. I paid double what a clone would have cost however after the conversion the engine started right up and has not skipped a beat.