Before touching the carburetor :

The VW Engine Health Check as original VW Service Dealer

With the Engine cold:

Check valve clearance:

Check Compression on all cylinders is with a compression test kit such as this one:

https://air-cooled-parts.com/product/compression-tester-kit-petrol-engine/

Remove all spark plugs and insert the relevant component of the test kit into each spark plug hole individually and turn the engine over on the starter only (5 – 6 times) , do not start engine! Ensure coil is disconnected from distributor.

Guidelines:

(140psi per cylinder when new) (100-140psi acceptable) cylinders must be within 5% of each other readings to be classified as healthy, below 100psi means its time for a rebuild or to replace the engine

—main suspect is No 3 cylinder

Check spark plugs – either gap to 0.025” with a feeler gauge & clean

https://air-cooled-parts.com/product/eeler-gauge32-piece-metric-imperial-lt2481/

Replace plugs if due for change correct gap = 0.025”

Correct plug =

Check Ignition Timing = 7 degrees static true— some variation allowed

Check all ignition Leads and cables for wear (scuffing) or bad connections.

https://air-cooled-parts.com/product/ignition-cable-set-bosch-111998031a-2/

Check points for pitting (should be changed at 12000-mile intervals) ensure gap = 0.015”.

Check condenser & coil (general condition, ensure you have spark).

A good upgrade is to fit an electronic ignition unit. (article on this coming soon)

Change the fuel filter and air filter if due.

Take a short run to get up to normal running temperature, check for any oil leaks from the valve covers.

Now attend to carburetor tuning only of necessary.

Should the oil light blink on tick over –manually check the oil pressure using a mini gauge such as this:

Screwed in in place of the oil pressure switch.

Drain oil if an oil change due, clean the oil filter gauze, renew the oil sump gaskets, replace the sump plate. Refill with oil 20W/50 + zinc

Some numbers to verify health of the engine:

Valve clearance for standard beetle in inches 0.04 exhaust 0.06 Inlet

Spark Plug Gap in inches                         0.025”

Spark Plug Type Beru                                W8AC

Points gap in inches                                    0.015

Ideal tick-over speed warm                      850 RPM +- 50

Oil Pressure hot tick-over                         20 PSI ideal, 10 PSI minimum

Oil Pressure 3000RPM hot                        ideal 45 PSI, max 50 PSI,  min 35 PSI

Cylinder Head temperature                    300 C max at spark plug base hot