Aprilia SR50 DITECH/general 50cc 2t compression ?

[modd1uk]

Have an aprilia sr50 ditech scooter here that i bought as a project to learn a bit about scooters as ive never worked on one before.

I dont suppose anybody knows what sort of compression reading i should be getting on it ? It had seized in the past so fitted a new piston and there was little damage to the bore...but the compression ratio is listed as 12.5:1, and at sea level my compression reading is only 90psi...i get the feeling it should be well over that ?

Anybody any idea ? or just a general 50cc 2t scooter compression reading.

cheers guys

https://www.youtube.com/watch?v=wEllJ7ySQGo
Trying to start.

https://www.youtube.com/watch?v=7WzD74cBUo4
Showing spark/fuel/air. The injectors are all in working order but it just will not work
____________________
2005 ZX6R ( 636cc ), pazzo levers, Jardine dual exit carbon, k&n, R&G everywhere, Black DB screen etc etc

[cheekythomas]

Cranking pressure on the ditech will be low for a while, as it uses some compression pressure, to back feed the compressed air circuit which is needed for the injection system to operate.

Youll see the injection system has a compressor unit fitted onto the crankshaft assy to supply the high air pressure... to save the engine having to whirl over for ages to allow the pressure to build up when started, it opens the injector without adding fuel, which allows air pressure to escape into the pressure regulator and pre-prime the system ready for instant use...

Its the reason why even a perfect running example wont fire up straight off the button, it needs a couple of cycles to sort itself out first hence the slight delay.