very odd problem

[judgie]

just fitting up a 1915 type 1 motor with 041 heads, 110 cam and a pair of kadrons. all brand new.
will only run on the front 2 pots.
have changed dizzy (trehaft 010, 2x 009), cap, leads, plugs also tryed a pair of 40 dells with no differance. valve clerance is all good and valve lift looks good and even between all pots. have chacked to see if the heads are for long reach plugs. retimed the engine from scratch at least 4 times.
this was a turn key motor and ment to have been bench run so all should be ok.
getting to the piont of pulling the motor out and pulling it apart, but customer is reluctent to have this done as has spent a lot of money on a built engine.
i did not build this motor and will not give out detials on who did, unless it proves to be somthing they have done.
thanks in advance for any ideas