Benny and the Jets

A whole bunch of stuff arrived today and I was most keen to try the new jets I’d orderd.  I’ve gone up one size for the primary and secondary main jets;  1.2 for the primary and 1.25 for the secondary and have half sizes to try as well (1.15 & 1.2).  The new idle screw and 'O' ring arrived along with new lock nuts for the air filter and 8mm spacers.

Installation is straight forward just be careful not to damage anything or drop anything down the carb venturi's!   A cloth stuffed down them helps.  The jets are accessed without having to remove anything other than the air filter...the factory fitted jets are 1.10 & 1.15 and both where a bit stubborn and refused to pull out of the emulsifier tubes initially but they gave way eventually with a little persuasion.  With the new ones installed I fitted the new idle screw and set it 1.75 turns out as previously.

I had to operate the choke manually due to the broken cable and BART fired up on a the first turn of the starter.

When he had warmed up I noted the idle was higher than before and the exhaust smelt a bit rich, I adjusted the idle screw and found the default factory setting of 1.5 turns was just about spot on.

Time for a test drive.  Ive written previously how well BART was now driving and willing to rev.  well things have just got a whole lot better.  To get BART to rev previously did require quite a large input from the throttle but now with the larger main jets the engine is much more responsive and eager even on small throttle openings...a slight press of the gas pedal now gets an eager response from the engine.  From 4K rpm opening up the secondary choke produces a real surge from the engine which was somewhat diluted before.  I'm not sure I'll need the half sized jets after this, I'll check the plugs after a few miles and see how they are holding up.  The car is now even more a joy to drive.

Next I need to play with the ignition timing, I've read that a little advance with the exhaust and increased jetting may bring benefits from the factory 5deg BTDC...

Addendum:
I tried tweaking the timing advancing to 10 and 15deg BTDC but didn't really notice any difference in performance, there may have been a bit of a loss in fact especially at 15deg but I wouldn't swear to it, however, what I did find was the engine seemed to run a little hot and I had to increase the idle mixture after a drive so it would idle cleanly...in the end I decided to set the car as Fiat intended at 5deg BTDC and 2 turns out on the idle screw.  This seemed to be the best setting so far.