Hello moped nerds out there, hoping to get some input on this build:
new style aluminum metra65, mild -- exhaust widening.
mlm people's pipe sidebleed
19 del @ 82 main
treatland cheapo cdi with pietcard box
really really old "70cc" head from like 2006 without a super defined squish, but has a bit of a slope and a medium sized chamber.
Out of the box, I used aluminum spacers and some paper to boost the cylinder to clear the exhaust. Measured up, looks like it is running about 131deg trans and 170deg exhaust.
Did some riding and break in, ended out with
jet about 82
timing retarding about 21->16
compression tested showed an abysmal 90psi (probably from boosting cylinder 2mm)
Goes about 45-49ish so maybe creeping up to 9.5k-10k? no tach.
Still runs pretty dang hot for such little compression -- gets up to 390 or so after a 2-3 miles of WOT with some up and down.
The main issue here is that it feels lean up top, surges a bit at top speed. If I bump the jetting any higher, then it sputters and 4 strokes a lot mid range on WOT from a stop --> so upping the main makes riding crappy and unfun.
I'm not really trying to go any faster, this is supposed to be a dumb easy around town bike, just trying to shake out this annoying problem.
So, how would you approach this:
Could be a port timing problem? -- seems like a lot of transfer duration for that ex timing.
Could this be because my compression is all low? -- I don't really seem to have the thermal credits to go bumping it, although maybe getting a tighter squish could help with temps.
Would you address this as a carb problem? -- Maybe some airbox or some air passage drilling would help even this out -- although never really had to go ham on a dellorto carb before.
thanks in advance smarty pantses (edited)