Scooterotica

Sorry if this has already been covered but anyone using Harry's stg4 200 setup, happen to know the realsitic squish band measurement. the edge of the piston wall sits a good 4mm below top of barrel and I have been advised to swap the 1.5 packer for a 1mm packer. Motor pinks at mid-high revs ignition now set at 17 degerees,

Eibar wrote:Sorry if this has already been covered but anyone using Harry's stg4 200 setup, happen to know the realsitic squish band measurement. the edge of the piston wall sits a good 4mm below top of barrel and I have been advised to swap the 1.5 packer for a 1mm packer. Motor pinks at mid-high revs ignition now set at 17 degerees,

Are you saying you have a 4mm squish??

exactly ! exhaust port perfectly opened at bdc so looks right with packer on. 0.5 mm head recessed into the barrel. Puzzled !?

Something doesn't sound right with what you are saying. Do you have a standard 57mm crank and 110 conrod?

The ideal squish should be 1.2mm but depending on what you want to use it for you can change it either way. 4mm is way to much for any use though

if his head is recessed 0.5 into the barrel then hes saying he got 3.5mm squish, not quite as bad as 4mm LOL LOL

but still about 3x the right amount

Just to know. Does that head have the proper squish angle and band or it is like an original head? I don't know that kit.

One I did with Harry's advice using a 1mm pack plate had the head skimmed and re profiled to drop the squish into the bore by 1.2mm. Prior to that it had 4.53mm squish as standard.

huge /non squishes ,with small head volume combined with huge jetting (to try to compensate the pinking etc ) really doesnt work does it hence the rather low bhp and torque figures that I have seen from these tunes .

I can machine head back further to get the desired squish but I aint convinced the design of the tune could cope with 1.2mm and i cant really find any concrete evidence to tell me this size of squish would work on Harry Barlow tune. I,ve heard the term "non squish" referred to this setup before and I just wanna eliminate the pinking which currently ain't happened with jetting and ignition changes. So do i reduce packer by 0.5mm and machine another o.5mm off head.

has yours been ok Wack

The motor resides in a custom Vespa "Flanders Fields". The owner does the Rallies and wanted something reliable with a bit more umph which he says it delivers. He's not a fast rider but did say the speedo now goes past 70 easily whereas it struggled to do much over 60 before with his weight. So far all been good , I too thought that a squish so large would be detremental but Harry has probably done loads of these tunes and experimented with various squish sizes till he was happy?