CB500s with G (Germany), E.D(European direct) or NL(Netherlands) designation had it along with 649a carbs instead of 627b carbs like the rest of the world.
As a matter of fact the 649A carbs were also on 500s shipped to Italy, Switzerland and other countries.
I don't know if apart from the jetting there are more differences between the 627B and 649A carbs like in venturis. What I
do know is that my 500 perfoms best overall with the 649A in standard set up and the air duct in place. Out of curiosity I've tested with 100 main jets and duct removed and so did others. Result: no gain but a lot more intake noise. I've imitated the setting as prescribed in the American Honda booklet and was not satisfied at all. I suspect an error or... (see below).
Why Honda had the 649A carbs for many European countries I don't know. There were no demands on emission or restricted power output. On the contrary: German, Dutch and Italian markets have always been the most competive markets for maximum performance. Countries like Germany, Holland, Switzerland and Italy always had the best gasolines for high tuned engines. There may have been a maximum on intake noise in Germany but that is not confirmed. There may have been a desire for a better shielded air filter (to prevent ingress of water). Overhere motocycles are serious means of transportation and not just for recreation. When with #78 main jets I remove the air duct there's a slight hesitation in midrange (flat spot) when accelerating. That's it and with airduct in place all is fine. At top speed (179 km/h in various tests, 170km/h with 90 kg and 196 cm of me, 185 km/h on the dyno) it runs on the rich side as it should.
Jetting recommendations for USA differ from ours
but also from the 500s shipped to France and UK that also had #100 main jets, no air duct. That is strange and leads me to the conclusion the 500s in USA had to run leaner at/near idle than in other countries, since for France and UK the recommended needle position was, like on ours, in 3rd (middle) grooove and the airscrews were one turn out +/- 1/8. All these variables play a role and don't be fooled by schematic graphics that always are a simplification. That's all I know.
