I have a nissan sunny fb13 - engine type ga15ds - carburettor. I have a problem with the carb. The mixture control solenoid has an o ring that goes at the bottom end of the solenoid. I have replaces the rubber but my car bogs on accelaration, if I ease onto the accelarator pedal it will run fine but if I try to gun it it stumbles badly. How can I fix this please?