TOPIC:

So my 1983 J3 runs well, it has allegedly hotter cams and definately pods with a V&H system, but it is VERY thirsty
with at least a litre per 10 kms normal driving The main jets are ridiculous at 172, someone realy took a shot at the moon and I suspect
this is the main culprit. Where should I start when trying lesser ones, 140?

Try this instead of a wild guess

www.factorypro.com/tech_tuning_procedure...igh_rpm_engines.html

The needle position will play a huge part in normal cruising fuel economy. Cruising a highway at 60 to 70 mph, you will only be in the 1/16 to 1/8 throttle range which is affected by the needle more than main jet, but the main jet still plays a part.