I have a missfire in cylynder No 4 , I have changed the plugs and leeds but the problem persists

Mr Hans. You said replaced the sparks as no7 was missing or missfiring. I take it for missfiring. Now you removed 8 ht leeds and removed and renewed 8 spark plugs. Possible cause of the random missfiring you have is, either not properly clicked the leeds to the spark plugs, or your leeds are old and by removing them are cracked, or slightly moved from the distributtor cap. Check for these issues. To disconnect the battery is not the solution. I believe you have HT leeds issue.

over haul the carby as the problem will be in blocked jets and float levels

SWAP COIL LIKE FROM CYL NUMBER 1 TO 4 AND ROAD TEST UNDER LOADS IF CHANGE THE MISS TO CYL NUMBER 1 NEED A COIL OR BAD PLUG AT CYL NUMBER 4

ECM may require a CKP relearn. Use of scanner required.

Has the timing belt or chain ever been replaced?

I would be concerned about sediments in the fuel rail. The fuels we use these days cause a lot of corrosion.

Hi,
A plugged fuel filter will cause these symptoms. Also a plugged air filter.
If the filter has been changed then the turbo and all related connections need to be checked, If problem still persists the one must check the injector pump.
Good Luck,
WAYNE

If it has miss and hesitation only warm not cold you may have a coolant temp sensor problem . but if the service engine soon light is off i would chek ignition system(plugs, wires ,boots).most likely one of the cylinders missfires when hot.

do a compression test ?? about 180lbs anything less and it could need a valve regrind ,if compression seems ok then plugs and leads and use the bosch plugs with the 3 electrodes (for voltswagon) champion are **** and missfire.if still persists change dist cap and leads

its only an idea but the engine management on the early beetles was a bit primative if your confident swap the injectors over from nos 1-4 and then see if the random missfire moves from cylinders 4 to 1 if it does then you have an injector fault if not let me know as i am a vw master -tech hope this helps
as far as jennablackies fault goes it could be as simple as damaged plug leads which would cause a missfire have you got any fault codes because its obviously nothing to do with cat/lamda probes