The year, make, model and engine info needed.
with a subway sandwitch
This is a complicated process and is individual to each make and model engine. Basically adjust valves, adjust turbo waste gate, adjust injection timing, ensure the pump makes correct pressure and volume, ensure the nozzles or injectors perform correctly and don't leak.
I believe it a engine on the back with valves
This question is not answerable without make model year and control system for the engine.
What make/model/engine size is it?
hai iam manu i haVE A ford laser gl 1992 model in 1990 model for laser engine is different from that of 1992 gl model its engine is quite new the engine is mazda b platform engine with 16 valves but the old engine has only 8 valves so that the performance figure is different compared to the old drivetrain has also been immproved simultaniously a lpt. they are different series engine no similarities
If it is a 1.8 or 1.8t it has 20 valves. (4cylinder 5 valves per cylinder). UK model with 2.0 engine different but so slow does not deserve to be called GTi.
you don't the lash on a 90 model is not adjustable. the valves are hydrolic,unless they have been replaced with manual ones.
I'm no mechanic, but from what I have read, the later model engines have hydraulic lash adjusters that can be tested and replaced(Haynes manual).
The most popular place I know of for instruction is the YouTube site at the link below.
It is not possible with many vehicles now. The year, make, model and engine info would help.