While working on the distributor as u advised i got little confused as normally vacuum advanced distributors are fitted with one vacuum line but mine is connected with two lines. can u plz explain me purpose of these two lines and plz also let me know if this configuration is better or single vacuum line distributor ??? as i read following in some auto discussion forum on net
"""""""Dual vacuum advance distributor
When I got my '68 302 it got 8 MPG in a '68 Galaxie. It also ran like a dog, hardly moved off the line, and didn't have much oomph up top either. My '67 Gal with a 289 and the same drivetrain got 14-15 MPG typically and was rather quick, blew away the '68.
Just going from the dual vacuum advance/retard unit to an adjustable advance unit got me up to 12 MPG. Not a single other change to the car. It also worked wonders for acceleration. It could actually get out of it's own way! After advancing initial timing a little too and rebuilding the carb and a whole tune-up I managed a high of 17 MPG highway and 14 around town. Timing is not everything, but it's damned close!
The purpose of the advance/retard unit was to control emissions. It also has a side benefit of if the car was overheating it would switch the advance vacuum from ported to manifold to give more timing at idle, raising the engine RPM and thus pulling more air through the radiator helping to cool the engine down. Not sure how much it actually helped but I do know that on the couple occasions I've overheated simply raising the RPM a little cooled it back down pretty quickly. The more timing the cooler an engine runs, the less timing the hotter it runs (since more energy and burn time of the fuel is wasted)."""