Cu engine not running on lh bank

[crazydiamond]

Im pulling my hairout. 
2LT cu Aircooled
 on lpg or petrol, new plugs and leads and tried old leads and plus as well. Found a manifold leak but fixed that with new gasket its still not firing on LH bank of cylinders.
On tickover thats lumpy pulled ht leads of each plug to see the  difference,
Cyl 1 idle drops
Cyl 2 Idle drops
Cyl 3 nothing happens
Cyl 4 Nothing happens

There is a spark at all leads but appears slightly lower on 3 and 4
I did a comression test on cyl 4 it showed 120

Replaced the amplifier  no difference
Tried the paperclip test but couldnt get a spark? 
The engine runs but obviously not very well

Where to go next? Im bamboozled

 

[silverbullet]

Must be the season for it! Sounds like no fuel delivery to that side or - assuming twin carb - the linkage isn't opening the throttle to the LH side so nothing is getting through to be ignited.

[Aidan]

Geoff should have updated the post, his manifold has parted company with the carb flange so pulling in vast amount of air after the carb/gas inlet, too lean to run, hence the wanted post

[silverbullet]

Yeah that would do it!