Hello I have recently changed the engine in my mk2 fiesta. It had a 1.6 cvh carb in before and have just changed the engine to another 1.6 cvh carb, using the same carb from the first engine. I have pretty much changed everything to new. I am no mechanic and this is my first engine change. Very proud of myself lol.
so my problem is It will start up after a few cranks but won't idle on its own without constant throttle.
is this a timing issue?? Its not fuel or spark.
thanks for reading

 

It could be a multitude of things, but I'd start with ignition timing if the distributor has been disturbed (or if you swapped it from your original engine). Then cam timing.
Then it will be a setup of the carb - just cause the engines are the same, doesn't mean they breathe identically so it may have put the balance out of whack.

 

Even the MK2 Fiesta had two different XR2 engines. Pre- and past-86. Early ones are LUB, hemi, ESC-ignition, Weber 32/34 carb. Later ones are LUD, heart-shaped, distributor without external ECU, Weber 28/32 carb.

There could be something wrong with the "new" engine or you might have forgotten a hose and now have an air leak -> engine running too lean -> cutting out. Also when you think you didn't change anything on the carb's setup... might still need a new setup. Plus moving it around might have damaged a seal or something else.
Won't be a bad idea to take the carb apart, put in a repair kit with new gaskets etc. and give it a proper setup.