Fuel Economy

I was delighted when I first learned that my son's Bug was pushing 30 miles per gallon (36 per Imperial gallon). We got 29.1 mpg on the trip to Utah.

Excellent fuel economy for a 1600tp. The Super is a little heavier too, which counts against it fuel-wise, so 30 mpg US is very good - most folks there report 26-27 as good. My '70 Bug used to get 36 mpg (Imp) overall, and almost 40 mpg on a trip at 60mph.

I occasionally ran my Bug dry just to see how far it would go -- 320 miles on 10.6 US gallons (30.2 miles per US gallon). Once I tried driving very sedately on a whole tankful and got 350 miles -- 33 miles per US gallon. That was before he became a 1600, though the fuel economy was still very good then -- it only dropped a mile or two.

1. Kind of Car: VolksWagen Brasilia 75, the same as sedan or Beetle.
2. Engine: 1600, it has a (vacuum) port in manifold and two in the carb, one to the distributor and the other connected to an additional port in the carburetor?
3. Pulley -- one notch.
4. Carburetor -- 34 PICT/3 Bocar Solex "California" Main Jet 127.5
5. Distributor: Mechanical advance + single vacuum advance.

Important points:

• Electromagnetic cut-off valve disabled. (the "head" is cut off)
• Timing: 5 degrees ATDC
• Points: 0.016"
• Spark Plugs: 0.025"
• Valves: 0.006"
• Carb: Richness screw 2.25 turns out; Bypass 3.75
• Carb. Automatic choke opens fully in 3-4 minutes
• Warm-up thermostat: doesn't exist.
• Engine Oil: SAE 40 most common here in Mexico
• Gearbox Oil: SAE 90

There is a vacuum port at the bottom rear of the carburetor to which is connected the retard vacuum port that is in rear of the carb. And the normal vacuum port is connected to the distributor. Additionally the mainifold has a port blocked.

I don't have a tachometer or stroboscopic timing light, everything was done with the above specifications.

A few points -

• The port you refer to at the bottom rear of the carburetor is set at an angle -- is there also a port sticking straight out of the carburetor -- close to the angled port?
• When used with a DOUBLE VACUUM distributor, the straight port (if there is one) is used for the retard vacuum line and the angled port is used (in California) for the throttle positioner.
• But you say you are using a single vacuum distributor, so the only connection to the carby should be to the vacuum port in the left side -- just above the throttle shaft. THIS is the advance vacuum port.
• When using the 34 PICT/3 carburettor with a single vacuum line, you must block off the port(s) on the rear (in VW-speak, rear is rear-of-car) of the carburetor so they don't leak air into the carburetor.
• And when using a single vacuum distributor you MUST set the timing at 7.5 degrees BEFORE TDC (7.5 BTDC), not 5 ADTC, which is only used with the double vacuum distributor. If you are using a single advance distributor at 5 ATDC timing the car is running very retarded and this will certainly give you bad fuel economy.
• So try making a new mark 18mm to the right of the single notch on the pulley - this is 7.5 degree BTDC (if that existing mark is indeed a 5 degree ATDC mark), and time the engine (static - engine off) at the new mark.
• Poor fuel consumption is usually a result of a blocked carby (the car will run poorly too), incorrect timing (I think this may be your main problem), or poor compression (worn out piston rings or burned valves).
• Have you done a compression test? With a good 1600 engine, you should get about 130 psi or more for each cylinder. As the engine ages, the compression slowly drops, until one or more cylinders are under 100 psi, then the engine needs a rebuild. With poor compression the engine will still run OK but power will be down and fuel consumption rises very fast.
• Type of fuel -- do you have normal gasoline or are you using a gasohol mixture? I know that gasohol (alcohol/ethanol blends) are common in Mexico.
• If you use gasohol, your fuel consumption WILL be higher, because alcohol has less "fuel" in the fuel. And if you use gasohol, you also need a larger main jet, so the fuel mixture is closer to ideal. Using gasohol with a normal 127.5 main jet makes the engine run lean and hot.

10% alcohol/ethanol blend needs a 132.5 main jet.

• Altitude also makes a difference. For each 5000' altitude the engine runs about 2 percent rich, so you need a SMALLER main jet - 125 for example.
• Just to explain that further - if you live at 5000' and use alcohol blend fuel, that's one size smaller for the altitude (125 size) but 2 sizes larger for 10% alcohol blend fuel, meaning one size larger overall (130 size).
• The SAE 40 engine oil and 90 gearbox oil should be fine for a warmish climate, but if you get freezing temps, the 40 engine oil would be better as a 10W30, just to make engine starting easier.