SOHC.co.uk Forums > CB500/550
CB550 - full trottle performance
Erny:
to avoid misunderstanding - tubes on pic are both keihin, left one is from 069A carbs right one from 022A carbs, both are used, coming from carbs refurbed by Gerben.
Keyster (new) tube is NOT on the picture (forgot to take comparison photo), but it looks EXACTLY as 022A, so all holes equal, OD, and other dimensions are the same.
I edited previous post - put text comment into pic to avoid confusion
Laverda Dave:
--- Quote from: deltarider on May 26, 2021, 10:50:29 PM ---When your 022A carbs are stock, there's only one notch left to raise the needles...
My gut feeling is somehow air intake is not correct. Also realise today's gas is not the same as in the 70s: with ethanol you can expect a leaner running. Like K2-K6 suggests, you could try a bigger MJ. But me personally, I'd first try - strange as it may sound - with the airscrews turned in half a turn.
--- End quote ---
That's a very good observation. Maybe try a thankful of super unleaded first and see how it performs. Less hassle than fiddling around with jets, tubes and needles. Personally I use Shell V-Power in the Jota, anything else and it feels flat and pinks if given full throttle quickly.
Erny:
With regars to fuel - I only use premium fuels to my bikes where possible, usually 100 octan, with 5% of ethanol max (E5). Standard fules here have 10% (E10)
I still suspect too lean issue might come from tubes being too small ID (Keyster). Need to check that before hassling with MJ and/or needles
deltarider:
I don't know where your airscrews are set now, but I'd give it a try with them. Honda specifies 11/2 ± 3/8. I can almost predict how theorists will react, but let me put it this way: my CB500 never understood that theory. It's done and undone within a minute. Could be the easiest fix.
K2-K6:
Octane in absolute terms is associated primarily with compression ratio and wouldn't change the mixture. It's mixed in with the causes of "pinking" with lean mixtures but the two reasons (too low octane induced, overheat conditions) need to be considered separately.
The overall experience from plugs and riding description are saying too lean, although not by much, which need to be addressed to bring it into more normal combustion performance.
The idle jets won't affect the upper ranges of rpm from adjustment of the air screw, but only if you changed their size. Once the idle jet reaches maximum flow it can't contribute more however the screw is set. The adjustment alters the slope of gain for idle jet flow and not the maximum.
Air screw further out will bring maximum flow at higher speed, in comparison to turned inwards when the idle circuit will reach maximum flow at lower rpm.
Worthwhile for some contingency protection while running is to raise the plug number by one to mitigate against plug tips going over temperature potentially causing pre-ignition, which you really don't want.
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