JBugs Video Series

VW Super Beetle Carburetor Tuning:

VW Super Beetle Carburetor Tuning

Video Overview:

With the engine for our 1971 Super Beetle project started and through its initial break in run, we can take a quick look inside the valve covers, fix some minor issues and then continue breaking in the engine. While the engine is running we’ll tune the 38EGAS carburetor for the larger 1800cc displacement and after we’ve run the engine for another 15 minutes, we’ll drain the oil, check the valve adjustment and call it a day! If you have any questions or comments, let us know below and of course, if you like our video, give it a thumbs up!

Video Tips:

The tools you will need are:

12mm Wrench
13mm Wrench
3mm Allen Wrench
5mm Allen Wrench
3/8" Ratchet
10mm Socket
1/2" Ratchet
30mm Socket
Adjustable Wrench
Needle Nose Pliers
Wire Brush
Small Flat Head Screwdriver
Medium Flat Head Screwdriver
Large Flat Head Screwdriver

Chemicals Used:
Copper RTV
Parts Cleaner

Video Transcript:

Hello! Sam here with JBugs.com. In our last video, we started up our 1800cc stroker engine for its break-in run. It went smoothly and we ran the engine for 15 minutes to get the cam and the lifters are worn in together.


Now that the engine had cooled off a bit, we pull off the valve covers so we can make sure everything is as it should be. The first thing we see is that the end bolt on one of our rocker assemblies has come off. Fortunately, no harm was done so it's reinstalled and tightened. We double check that the three other end bolts are tight then the valve covers are reinstalled. We aren't concerned with the valve covers leaking a bit as we will pull them off again in another 15 minutes of run time. The oil return adapter bolt is tightened a bit more and we start the engine up again. We want to run the engine for another 15 minutes for a total of 30 minutes before we change the oil for the first time.


While the engine is running, we can dial in the carburetor. With our timing light, it's very easy to see the adjustments at the carburetor effect the RPM of the engine. The tuning can be done, and some people prefer, tuning by ear while listening for the RPM change. We first set the idle mixture screws to the best lean idle by turning the mixture screws in until the engine starts to stumble. We turn the screw out, a quarter turns at a time. The RPM should increase and the engine will run smoother. We continue turning the screw out until the RPM drops or the engine begins to stumble again.


Next, we turn the screw back into the point where the engine ran its best. This is usually the highest RPM point or where the engine sounded the smoothest. Both of the idle mixture screws, the one at the face of the carb and the one against the fan shroud, are adjusted the same way. Both are adjusted before the idle screw is adjusted. Once the mixture screws are set, we can set the idle screw at the carb linkage and adjust it until the engine idles at about 850 to 900 RPM.


With the carburetor tuned, we'll go back and double check the timing. [The] distributor clamp is loosened and we hook up a timing light. With our timing light advanced to 30 degrees, we point it at the crank pulley at the split in the case. The engine is revved up to about 3000 RPM and we look for top dead center to show up while slowly moving the distributor. When it does, the timing is set and the distributor clamp is tightened down.


Now we can run the engine for another 10 minutes or so to complete our initial break-in run. During this run, we don't like to let the engine sit and idle continuously so we run through periods of revving and idling. This will ensure that the piston rings don't wear the cylinders at any one position. While we are running the engine we noticed that if we accelerate the engine slowly, the RPM increases without hesitation. However, if we accelerate the throttle quickly, the engine will backfire a bit before the RPM increases. This indicates a lean running engine so we need to richen up the carburetor by installing larger main jets and possibly larger idle jets.


After we run the engine for another 15 minutes, we turn the engine off and roll it back inside. Once the engine had cooled down a bit, we pull the sump plate off slightly to drain the oil while looking for any large debris. The oil looks as it should and we can see very small particles that should be expected from running a new engine. With all of the oil drained, the sump plate is removed completely along with the gasket. We pull the oil pick-up off remove and clean the screen which has some gunk and debris on it. The oil passages inside the engine most likely had some old gunk that didn't get flushed out completely. The screen did its job though and once it’s cleaned it's reinstalled on the pick-up tube and pushed into place.


A new sump plate gasket is installed and followed by the new sump plate. The engine is refilled with oil. We pull off the valve covers and turn the engine over to number one top dead center .We check and adjust the valves. The other three cylinders are checked and adjusted as needed. New valve cover gaskets are coated with copper RTV silicone and set into place on the valve covers and the valve covers are reinstalled.


All the oil that leaked earlier is cleaned up and we'll take a break here until next time where we'll pull the carburetor off, rejet, reinstall and retune it. While you're waiting for that video though, check out some of our other videos or stop by JBugs.com for all the parts you'll need for your vintage Volkswagen.