help engine cuts out

i got a 1.3 and changed it to a 1.8 as when at hight revs it would cut out so was going to gange the gear box but did the engine too. i thought this ould help but the bug is back.

when at high revs it judders and when you clutch it it dies then is a pain to start for a while.

i know the endgine is good and have a new rotor arm cap and plugs so please any ides

If you changed the engine and a similair problem is still there, i would be checking the fuel system. Sounds like its needing a clean out. check the filter thats is in the fuel tank as these clog up and cause problems.

Did you change the other things you need to run the 1.8 engine?  I think there is a lot more too it than a straight engine swap i.e fuel pump, tank etc.  As above, if it's always been there I'd check your fuel lines, your fuel filter and check that your filler neck is not corroded?