TECH TIP Technical Index

Carbí Adjustment


Yeah, right! That ainít the way MY VW IDLES. So it isnít? You put new spark plugs in, new points or adjusted the old ones, and set the timing. After all that, your carburetor may not be adjusted correctly. Iíll guide you through the right way to adjust your carb on í70-up VWís. Thereís no rocket science about it, just a few tools and a little information is all. Grab a small regular-tip screwdriver, a medium-sized regular-tip screwdriver, 13mm combination wrench, a handheld tachometer or one of those fancy timing lights that has one built in, safety goggles, and carburetor cleaner.

I am going to assume here, that all vacuum hoses, intake seals, and carburetor gaskets are new or good condition. If not, take care of those before you touch the carburetor, as vacuum leaks or fuel leaks will make any adjustments useless. Also, make sure the carb mounting is tight; check with the 13mm wrench. If the carburetor is gunky-looking, put on your safety goggles and spray the carb cleaner on it. Make sure you clean the moving throttle mechanisms and the adjusting screw areas especially well. And PLEASE wear the goggles. Iíve made the dumb mistake of not doing so in the past, and if you get just a tiny bit in your eyes, it will be painful, to say the least. After you have cleaned the carburetor down to the gray metal, you are ready to begin the adjustment.

On the throttle lever near the top left of the carb as you look right at it, there is a screw that contacts an extension on the carb. Take the small screwdriver and undo the screw until it doesnít touch the extension anymore. Now turn it back in until it juuuuuust barely touches the extension. Then turn it in ľ of a turn (or 90 degrees clockwise). You have now adjusted this part correctly. After you have done that, this screw will be off limits for any more adjustment! No toucha this one from this point on! What you just accomplished is to set the throttle blade in the correct position for metering some idle air and proper metering of idle fuel at the idle transfer slot. If the throttle blade is not adjusted in the above manner, you will have idle problems along with some off-idle "stumble". With the correct adjustment, the rest of the idle air and fuel mixture will be set with the adjustment screws on the left side of the carburetor, which is the next stepÖbe sure the engine is warm and the choke is off.

Now peep around the left side of the carb, behind the throttle lever. See the big screw on top and a small one on the bottom? The big one is the idle-air screw and the little one is the idle fuel mixture screw. Take the small screwdriver and slowly, gently turn the fuel mixture screw in all the way until it just seats. Donít force it. Now back it off 2 Ĺ to 3 turns counterclockwise. This is a baseline setting and should get you running. Connect your hand-held tachometer to negative side of the ignition coil and start the engine. Take the big screwdriver and adjust the big screw until the idle speed is around 900 rpm. Now take the small screwdriver and turn the small screw (fuel mixture) until you get the fastest idle speed. Now turn it in slowly (clockwise) until the idle just starts to drop a bit (20 or 30 rpm). Now adjust the big screw (idle air) to get back down to 900 rpm. Tip Ė if the weather is cold, you may not want to adjust the fuel mixture to where the rpm just drops a bit. Colder air requires a richer mixture to get the job done, so consider this if the temps are below 50 degrees. Remember on the idle fuel mixture, counterclockwise makes for a richer mixture, and clockwise is leaner. I may go into some of the scientifics in a later tech article.

Hopefully, this will help smooth some things out in the idle department.

Your VW maniac and Tech Specialist,

Mike C. Ė