Many people choose to get their VW's tuned by a specialist with all the equipment, like Sun or Krypton gear. However, worth bearing in mind is that aircooleds don't have loads of electronics, fuel injection, engine management, exhaust gas sensors etc, they just have one carb and that's it! And also bear in mind that there are only 2 screws to make adjustments with! Any other fuelling problems not tuneable by the two screws need to be addressed by changing the jets in the carb ....... that £50 tuning bill doesn't seem like such good value now does it?! Doing the same job by ear really is simple, that's the beauty of old VWs!

Firstly, get to know your way round your carb, it's a simple bit of kit really, just looks complicated. It sucks air in, mixes fuel with the air, then sprays the mixture into the inlet manifold for the engine to burn. The amount of fuel that gets mixed with the air is adjusted with screws in the body of the carb. This varies from model to model, but all have one large one [air bypass screw- idle speed] and a smaller one which is the main adjusting screw. Don't confuse the adjusting screw on the end of the throttle arm with the idle screw, it's just a throttle stop.

Before any adjustments are made, the engine needs to be hot and you should have checked the timing and valve clearances already. You'll need a short flat screwdriver, and a longer thinner flat screwdriver, oh and a pair of ears to hear the changes as you make the adjustments!

[NOTE:- be very careful of the fanbelt and pulleys as you do this procedure, youll be working round fast moving and hot parts]

Warm up your engine [don't just let it idle! That's a surefire way of wearing the engine out fast, always warm an engine up by driving it under light load.]

Once its warm, open the decklid, and with the short flat screwdriver, unscrew the big [idle] screw by a couple of turns, this will make your idle speed higher, and make it easier to hear the changes you make later.

Now carefully [ you don't wanna catch yourself on the fan belt while the engines running] screw in the smaller main volume screw. Turn it slowly, you will hear the engine note change, depending on how your engine was running before, this change could make it run faster or slower to start with. Either way, keep turning slowly.... after a few turns of this screw the engine note will slow and it will falter and stutter. Don't worry, this is normal, and in fact is exactly the scenario you want [If it dies and won't restart, just wind the screw out a little...].
Your engine is now running at its leanest [least amount of fuel in the mixture].

While it's still running [badly] we now want to wind that little screw out again. As you do this, the engine speed should pick up again, and the more you wind it out, the faster the engine seems to run, this is what we want.
Listen carefully to how the engine sounds while you turn the screw out. As you keep turning, you will notice that after a while the speed doesn't increase much more, and in fact if you keep unwinding you will hear the engine speed slow to a stop again as it did when leaning the mixture off.
You've now reached, and gone beyond the perfect idle mixture for the car, and now too much fuel is flowing through it. Our ideal point is where the engine was running at its fastest, so screw the adjuster in, until you reach that point, listening the whole time... when you think the engine is running as fast as it can, stop turning the screw, youve got your mixture spot on.

If your car is a 73 model or earlier, I suggest leaving this setting alone. The reason for this is that the setting you've just made will make the engine run ever so slightly rich, which in my opinion is good, as a lean engine[less fuel] will run hot, and on a long run that isn't so good! However, if your car is post 73, your emissions will be tested at MOT time and so you may want to give that little screw half a turn clockwise to give a clean burn. I leave mine as is, as i prefer a long lasting engine!

Now after all this fiddling your idle speed will probably be too high. Set it at the right speed by screwing the bigger of the two screws clockwise. You'll hear the engine note drop again, all the books and manuals say set this to 800-900 rpm, but always bear in mind that when the engine is cold, the idle speed will be lower, so i always set it a touch higher than this to account for cold starts.