1600 TP running rough.....running on 2 cylinders?

[1970Deluxe]

This is a bit random,but i bought a 1600TP as a shunter engine so that i can rebuild the original.The guy i bought it off took it out a while back as he has fitted a scooby lump and the engine has sat on a pallet since.I put it in weekend and it started first time but was shaking about and running rough on idle.I checked the basics and found that if you pull no1 or no3 plug leads off,it makes no difference to the running of the engine.The compression is roughly the same on all 4 cylinders and has a spark on all 4 leads.It has twin weber carbs which i havnt touched but the plugs that come out of no1 and no3 dont seem particularly wet.
I dont want to get too involved in it as like i said its only a shunter but i am intrigued.Will check the tappets if i get a chance but have got enuff jobs on without carrying out an autopsy :?

 

[sparkywig]

Try changing the plugs.

 

[BJ1]

Carb idle needs sorting on lhs. Blocked jet?

 

[1970Deluxe]

Just a quick update on this as its puzzled me now......

Checked the tappets which werent far off really.Swapped the coil,dizzy,plugs,brand new leads off my other running engine which made no difference.Took the carbs to bits and re-jetted for a 1641 and cleaned them throroughly.
Did a cylinder leakage test which didnt show up any problems and re-did the compressions again with a different guage but the readings are all pretty equal.
sooooo.....my thoughts are now based on 2 possibilities
A) camshaft lobes snookered on the back cylinders(does this happen?)
B) Bad air leak at inlet manifold or inlet manifold faces distorted.

I have sprayed brake cleaner around the base gasket and it does alter the running slightly so have ordered a pair of gaskets.

If this doesnt work i shall swap the good carb/manifold off my other engine weekend so at least i can rule the twin carbs/manifolds out of the equation