Sprint '99 St Poor Running

Newbie here and I'd like to finish off a thread with a result, rather than all the others I've read that just stop.

Apologies if it's a bit long but the more info given helps a lot..

Owned my '99 Sprint ST for coming up 2 years, never had an issue. Did a short 10 minute ride, started the bike again and there was a pop like a balloon popping followed by a whistle/squeak. but running fine. Rode back home just with the noise, engine running smooth but lacking a little power. Removed tank/air box and found number 1 vac hose broken (replaced with Triumph ones about 18 months ago) replaced all 3 with silicone hose, everything back on and missing on number 1 cylinder. All through this there has been no engine warning light on. thinking maybe coil/plug (plugs replaced with Iridium ones about 12 months ago) but tuneecu doesn't show any faults. I then went down the valve route, seeing pressure had returned up through the vac hose, compressions at 200 give or take 5 either way over the three cylinders. I've now replaced with standard plugs. I know it's not running on number 1 as that down pipe is a lot cooler than the others. injectors have been removed and cleaned/checked and number 1 ignition coil replaced. I have also noticed the fuel lines are opposite to the triumph manual 'suggestion' as in supply and return but doesn't even start if I connect them that way. Anyone able to shed some light? I've been trying to sort this for 3 weeks now and possibly read every forum thread on running issues.

 

Have Tuneecu and shows no fault codes