How to fix my mk1 golf?

If your exhaust system suffers flames and explosions then the cause is un-burnt fuel building up in the pipes...

If you have fuel vapor in the exhaust system then it's not being properly burnt in the cylinder.

Your engine may be suffering a loss of compression - fouled plugs or a weak spark.

I wonder why you felt it necessary to fit an "uprated" fuel pump - will it be squirting more fuel into the engine?

I know nothing about cars - no expertise or experience.

Peccavi
May 2013