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Have you tried the mixture screw as this can affect small throttle mixture as well as tick over . Supa 5 carbs are now all over 40 years old and worn so standard settings are mainly only good as starting points. Most supa5’s I have set up in recent years respond best with the needle on the leanest or leanest but one position and MZ’s carb parts vary I have seen two needles marked C6 but have visually different taper and lengths and some carbs with slides marked 70 and others not marked . Most of the carbs I am talking about were 30n2-4’s but parts may been changed over the years . Could your carb be off an early ETZ as I have never seen 30n2-5 on Supa5.
I run a supa5 race bike in the BHR club and I run 1mm clearance and have no problems revving to 7000rpm and the bike seems fine at lower revs . but in theory the tighter squish should reduce the chance of detonation but the higher compression ratio should increase the risk but as these engines are generally quite low compression this should not be a problem. generally high compression gives an increase in torque but tends to reduce power at the very top of the rev range and lower compression seems to give a flatter lower torque curve
most crown heights are measured from the top of the gudgeon pin hole ( check the Matika pistons sight though the do not list MZs ) . This seems to be what is used by most manufacturers , but I have seen tuning manuals where my have measured from the centre of the pin.
hope this is helpful.
Big Bill ( Dunstan )further to my previous reply a piston for Kawasaki ke175 ( disc valve ) may be closer to what you require.
billI tried to do something similar with ts150 but could not due to the head sealing arrangement, but did find that a Suzuki ts185 piston was very close to the mz ts piston which I think is different to the etz. the bantam big bore piston is a modified Suzuki ts185 piston. I believe the etz has a higher piston crown, but it may be possible to use the piston by shortening the barrel . by the way bantam racing pistons are available with a 15mm small end asper the mz in a various bores.
Bill
