If bad fuel you may be able to jazz it up with an octane booster and/or a fill with higher octane petrol. If draining the tank get a fuel syphon & go in via the filler first only then take out the pump. Fuel pressure testers a quite cheap, I got one of these not great quality or robust but only used once & much cheaper than a visit to a garage.
https://www.ebay.co.uk/itm/284354587588?hash=item4234daabc4:g:7vIAAOSwfppg3Wta
