power loss at 4000 rpm

Hello I'm a new mg tf owner, I have a 135 and have just installed an air induction kit picking up from the near side air in take, magnecor ht leads and nology silver core spark plugs, when re fitting the spark plug transformers they didnt feel like they fully engaged the spark plugs but there didnt seem to be any way of changing the ht plug length.

while test driving after putting everything back together the car feels fine at low revs and pull away but once I hit 4000 rpm the power drops out and the engine starts to chug.

the car ran great before the parts change.



Any ideas where to start looking

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