I have a 1976 Shadow with stock electronic ignition, it seems to be average approx. 11 miles per gallon, slightly better on the highway, but we don't drive excessively.
I did recently change the plug wires to a heavier silicone wire and converted the spark plugs to the Pulstar Pulse Plug, part number Be1. I e-mailed the company regarding any possible issues with these new style plugs being used in an RR and they were quite confident with their product as several other RR owners have experienced success with them.
While some may feel they're a bit costly and not worth the price of $24.99 per plug, I just had to try them.
I haven't checked my mileage after installing them, but I will honestly say, the vehicle runs incredibly smooth. I also balanced both carbs with pot-mount gauges with Sherbourne Mews.
The Shadow passed smog with flying colors three weeks ago, in fact, the smog station owner was very impressed at how clean the engine was running.
You can read about the plugs on their web site:
Overall, I'm very pleased! Our Shadow just purrs, starts easier, runs smoother and the acceleration does feel a bit more responsive.
Some may not recommend these new style plugs, but I've since installed them my daily driver (2005 XB) and can actually feel a bit more power
If you try them, please let me know what you think.
OH!!!! Be careful installing them as I cracked one by accident (front left) while installing in the Shadow and you can only by them in pairs. Well at least I have a spare.