I just swapped out a 1.6 to a 1.5 in my Honda civic. I am not getting any codes or any engine light on. The car seems to be running okay and idling good. But when I am driving and switching gears mainly in second gear the car starts hesitating like if I switched in to a higher gear but once it starts going then it s fine. I get the same problem sometimes in first gear on take off and through the rest of the gears if I put the throttle to far down it’ll start having that hesitation. But really noticeable going into second gear it seems like if I run the rpms to about 4-5000 before switching to second then it won't do it but anything under 3500prms then it starts hesitating until the rpms get back up then it goes back to normal. I thought that the clutch may be needs adjusting, but I don’t know why its doing this. Other then that the car is running great. Any help would be great. Thanks

You should check your timing if your timing is too much in advance your car will fire to urly and cause a lack of power same principale for a retarded timing your timing.
The timing for a d15b8 is 16 degres in advance and b7 12 degres or the other way around.
Check that out should be a good bet.