JBugs Video Series

VW Super Beetle Carburetor Rejetting:

Video Overview:

With our 1800cc Stroker Engine running and through it's initial break in and tuning, we can get our 38EGAS carburetor dialed in. We'll replace the primary idle jet along with both the main jets to better tune the carburetor for our larger than stock displacement engine.

Video Tips:

The tools you will need are:

Flat Head Screwdriver
Phillips Screwdriver
3/8" Drive Ratchet
6" Extension
13mm Socket
13mm Wrench
Needle Nose Pliers
Angle Grinder
Timing Light

Video Transcript:

Hi! I'm Sam with JBugs.com 

Now that the engine for our 1971 Euro Look Super Beetle has had some run time, we'll get the carburetor better tuned for it. The biggest issue that we've seen so far is that there is a small backfire if the accelerator lever is opened quickly. Other than that, once the mixture and idle screws are dialed, we've been very happy with the performance of the carburetor.

The small backfire tells us that the carburetor is running a bit lean on the top end. Another minor issue we can see when operating the carburetor with the engine off is that near throttle the accelerator pump linkage touches the alternator. This prevents the car from being able to go full throttle and that just won’t do.

So off comes the carburetor; we grind the pump arm down where it was contacting the alternator, and test fit the carburetor to verify that it no longer hits. With the clearance out of the way, we can now check and note the adjustments of the mixture screws.

The front primary idle screw is at two turns out and the back secondary screw is at one turn out. In general, if you're between a half and one and a half turns out the idle jet is the correct size. In our case the secondary idle jet is fine but we are out too far on the primary idle jet, so we'll bump it up one size. The primary idle jet is attached to a screw to the right of the choke. With the screw removed, the .45 jet is pulled off and replaced with a .50 jet and threaded back in place. Then we set the mixture screw below at the baseline one turn out.

With the idle jets taken care of, we will address the main jets and to access them we'll remove the top plate of the carburetor and set it aside along with the top gasket. The gasket is reusable as long as it isn't torn or dried out. Inside the float bowl at the very bottom are the two main jets, one for each barrel. Both of the jets are unthreaded. We verify the sizes at 145 and swap them each out for one size larger 150 jets. The top plate and gasket are reinstalled and the carburetor is reinstalled.

We’ll head back outside with the engine to run it and test the new jet sizes. With the engine running we check the primary idle screws first by turning them in until the engine starts to stumble. We turn the screws out, a quarter turns at a time, the engine RPM increases and the engine will start to run smoother. We continue turning the screw out until the RPM starts to drop again. We turn the screw back to the highest RPM point or where the engine sounded the smoothest.

We double check the secondary mixture screw using the same method and it was exactly where it needed to be. We reset the idle screw at the carburetor linkage and again adjust it until the engine idles at about 850 to 900 RPM. With the carburetor tuned, we'll go through and double check the timing to make certain we're at 30 degrees fully advanced. With the timing set and the carburetor dialed in we can note that the larger jetting has eliminated the backfire.

The engine is shut off and we can check the primary screw position where it is exactly one turn out, right in the middle of the adjustment range where we want it to be. We'll repeat the engine run cycles where we vary the RPM for a total run time of about three hours before we drain the oil again. Then we'll pull the engine down to the long block, we'll paint all the engine tin and other accessories; we'll check the torque on the cylinder heads and then reassemble all of the components. Then we can set the engine aside so we can get to work on the car its self.

Until then, check out some of our other videos and say hello in the comments below. Otherwise, feel free to check out JBugs.com where we've got thousands of parts for your vintage VW.