I've been experiencing a weird problem lately that I THINK is because my belt needs to be tightened.

What happens is when I accelerate hard and then take my foor off to change gears, I can hear the roar of the engine die but then there is almost an echo as another sound dies out just after. Is this the belt?

If so, how do I tighten it myself?

You can tighten the belt by removing a couple of shims from between the pulley halves. You can check is the belt needs tightening or not by pushing it with your fingers. The amount of movement from the straight position should be less than an inch. Does it make sense?
Raf

All except the removal of 'shims'.
Should I go to a mechanic?

If you are not confident - yes.

Otherwise read a manual

Idiots Guide
Gregorys
Haynes

These manuals will cover things like this and much more.
Yes - it is daunting the first time but these are simple things that will save you money.
Belt, valve, poit, timing adjustment are all really simple - once you know how.

By the way - shims are the spacing washers between the pulley halves. You either put them between the pulley halvesto loosen or behind the nut to tighten.
The trick is locking the pulley to stop it turning to undo the nut.

Hi

You can sometimes get that noise if you get a leaf or bit of rag stuck in the fan, just put you hand in the back of the fan and make sure all the blades are clear, its a good idea to have your keys in your pocket while doing this, for obvious reasons.

1302Steve

yep, sounds like the belt. make sure your pulley is not bent as the belt will go tight and then loose as it spins, hence making the roar as the belt vibrates. just start you engine and pull on the handbrake, out of gear, not on a hill, chock the wheel and then operate the accel from the engine compartment. you should see the belt vibrate as you accel and de-accel. then tighten the belt as described in your trusty VW book.

Another thing is to make sure the pulleys aint "flogged" out. The outer can round out and not mate properly especially if it is a new anodized one.
The best are original - even better are the ones with the mating tangs.

In you want another step ann even better thing "apparently" is i have read the a 356 pulley will fit. Unfortuneately i have lost the part number from a post i wrote down.
The 356 pulley is slightly smaller in diameter and spins the fan a bit faster annd cools better. Obviously you need the matching belt to go with it.