I’m surprised you only have 4 gears... I thought all later cars came with a 5 speed gearbox? Have you a picture of the gearbox?
If your problem is fuel related fitting a different engine may not fix the problem as you will still have the most of the same fuel parts still on the car....
Try what mr Brown said in your other post?
Mk1 78 Scirocco GLS 1.6 FR, weekend toy.
Mk1 88 Golf GTi cabriolet 1.8 DX. Daily drive.
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