I had a similar problem with mine a while ago. Needed the flap under the air filter held open to run.

I ended up removing the small block on the metering unit where the 4 red pipes that go to the injectors bolt too and changing it for a spare I had. It's held on by 3/4 small Torx bolts I'm sure.

Could always try removing it and making sure the fuel galleries are clear and not blocked up.

Just a thought. Hope you get it running.

I recently changed from MFI to EFI Defo worth a look these days as parts for the old system are getting hard to come by.