After 44 years of owning a CB500, the only advice I can give, when you are 100% sure it's fuel related and your bike is stock, is: to interpret your #38 or #40 jets just like Honda has called them:
slow jets and not 'idle' jets or whatever. Think auxiliary jets. Realise that these carbs lack acceleration jets. As a consequence the aircrews position
does play a role in acceleration/driveability.
In the past I've had a wonderful idle, the engine purring like a kitten, but I wasn't satisfied with the driveability. Then I remembered what a Honda mec (who owned a CB500 himself), had told me: that these slow jets also play a role somewhat higher up. He was right. From the rpm where the bike didn't accelerate well, when I pulled the plugs, they were whitish. When I turned the airscrews
in again to within the by Honda recommended position range, the idle was
not as nice as before,
but I was rewarded with a much better driveability and the flat spot was almost completely gone.
To some degree that flat spot
cannot be cured at all. Has to do with the engine design: 4 cylinder, displacement, bore x stroke, rpm range etc. I have forgotten the exact details, but I haven't forgotten how, when these bikes were tested and reviewed in the 70s, some expert had commented on this phenomenon and had related it to the design characteristics I have mentioned above. I seem to remember the word was: oversquare.
Then... if you say 'flat spot', what exactly do you mean? If you want to accelerate from say low midrange rpm without shifting down, you
will certainly experience what one could call a flat spot. But, if you accelerate from a standstill, revving in each gear to 7000rpm or more, there will be no flat spot. At least, there shouldn't be.
Here's my guess. Most older Americans ride their bike, the same way they were used to drive their cars of that period, the ones with ridiculously oversized engines: @ low rpm with plenty of torque, making childish
gurgle-gurgle noises. How I dare say that?
Well, look where there is a lot of complaining about deficient charging systems designed by Honda. It's only
here, not in the other fora, not in France, not in Germany, not in Italy. Realise how stupid the hidden presumption is.
As if Honda did not know how to make an adequate charging system!And exactly this has annoyed me for years now. If you want to profile yourself as an expert, it doesn't help you to praise Honda for this and for that. A much better strategy is to point at a 'shortcoming' and then come with a 'solution'. It works the same in advertisement: the advertiser says, or at least suggests, you have a problem and/or you are missing something. TATARATAA!! They have the solution. Isn't that wonderful?! It works the same in political speech. It won't help a candidate to praise what his predecessor has done and then promise he (the candidate) will continue the good work. Much better is to blame the predecessor for failings and if there aren't any, well, you can - just like in advertisement - make them up, in other words:
lie and exaggerate in the process. Also good: point to 'them from over the border', those that have always been contributing to the economy and prosperity - and picture them as criminals and blame them for poisoning... but let me stop here.
