Haven't posted here in a while, been trying to get the bike going

It runs, but then again it doesn't...
The bike had not been ridden for some months.
I have siphoned the fuel out and filled with 10L of shell 98.
It starts fine on choke, but periodically cuts out, if i push choke back in, it will run for a bit then start do drop[ in revs till it dies. if i quickly pull the choke back out the revs lift again.
Now, that said, even if the choke is out it will still eventually drop and die...
I do not know what to do, i have exhausted my knowledge....
It seems that the bike is only running on the right cylinder, but im not 100%
im going to get new plugs and try again...
Any ideas?
Adam