3A Problem

After all the hassle of putting a 3A in my MK1 I have started it up to find it has a misfire on number one and Two Cylinders.
Can anyone who has done this conversion help?
I have done it slightly different to most I have seen as I have used the original 3A Head, I had a plate made up so I could fit the Twin 40 inlet manifold to the head and I have not removed the breather? on the side of the engine block were the fuel pump is fitted on older engines, do I need to do that?
I have Twin 40 Dellortos fitted that have just been refurbished, so hopefully they are OK.
I checked the compressions before i started the motor and they were good, 175psi.
After finding the misfire I checked the compressions again to find 1&2 only had 70psi!
I have had the head off and crack tested and skimmed, the bores seemed to be OK as did the block and Head gasket.
I fitted a new headgasket and the misfire is still there.
I have a good spark although i am using the old 1600 dissy with points and i have swapped the drivegear off the original 3A dizzy.
As you can see I have been through quite a few checks and all to no avail.
I just wondered if i need to fit the 1800 carb head and blank off the plate on the engine block, does anyone know the main reason for doing this?
My only other thought was that with it missing on 1&2, was that the Carb was flooding the cylinders and washing oil off the bores? as both plugs are wet with fuel, I am running an electric Facet fuel pump through a Pressure reg set at 2.5psi.
Hope somone can shine some light on this for me.

the blanking plate is used when a mk1 head is used, as these breath through the rocker cover. this should not interfere with the compression issue though.
 seems odd that the comp would be o.k., then not. the fact that the missfire is on 1 and 2 would make me think that either the ht leads are on wrong or that carb is not running correctly.
  are they matched carbs? both jetted the same? linkage all right?

I bought the Carbs from a Carb specialist who had refubished them and he had set them up for 2.0 Motor so i asume they will be right!
The linkage is quite basic on these Dellortos as they just have a link betwwen the two carbs that you can adjust and the throttle cable fits onto one carb.
I may just take them back to him and get him to check they are set right though.
I have set the dizzy up right as far as i know it rotates clockwise and has firing order 1342, i have folowed the leads and they all correspond.
I was wondereing if the valve seat could be worn but as you say on two cylinder would be a real coincidence.
I think i will go get the carbs checked first.
Cheers.

you should be able to check the linkage by moving the throttle and seeing if both carbs butterflies open and close the same. not sure how the co is adjusted on twin carbs. do you adjust each carb? if so, that could be your problem. could also be an air leak at the inlet manifold. either head or carb end.

Just to let you guys know, I have sorted the problem.
Thanks Wooders for you advice it worked a treat.
The carb on no 1&2 cylinders had the throttles fully closed when i was doing the compression test and at tickover so she was really struggling to get any air in. As soon as i opened the throttles the compression went straight up tp174psi and 165 psi respectively and she ticks over and runs well now i have adjusted the the throttles, something as simple as that.
Sounds awesome too!
Thanks for all your help and advice

:y:

go have some fun now.