As Buffy mentioned, there may be no way to do this without ruffling feathers. Any "normal" excuse (I'm moving institutions, etc.) indicate that you don't have enough time to devote to polishing the paper, therefore your authorship should be adjusted down (i.e. from second to third author, or something), rather than removed entirely. Asking to be removed from a paper will always be interpreted as you saying very clearly that the paper doesn't meet your standards.
Thus, if your goal is to ruffle the fewest feathers, rather than trying to extricate yourself from the paper, determine what would elevate the paper to meet your minimum bar for co-authorship. Then, try and (respectfully, but straightforwardly) bring these points up with the coauthors.
Because think about what "leaving" the paper says: I don't have confidence in this work, and, furthermore, I don't believe you are careful/conscientious/ethical enough to listen to or address my concerns. If you respected these people enough to get involved with them in this project in the first place, respect them enough to at least air your concerns with them first. Then, their response can dictate your next steps. Then you will be on firmer footing if later you decide you really have to get off the article. You can say something like:
"Sorry that I really feel that the alternative explanations need to be explored prior to publication, but I can understand that you feel the additional experiments required don't match our current funding/timeline/whatever. In that case, especially because I'm moving and can't contribute to the future work, I'd ask you to remove me from the author list, but wish you the best in publishing and hope we can work together again in the future."