SOHC.co.uk Forums > CB500/550
CB500 runs lean and doesn't want to pull through
Sesman:
I’m a bit confused by this one and I’m watching and learning. I thought Erny began this thread stating he had a very obvious and extremely lean burn? This may have precipitated his subsequent query about appropriate air boxes/filters. Purely out of interest, would a single tooth cam timing error create this lean mixture situation?
Sounds like poor Erny will have to start a sequential diagnostic programme…..cam timing….ignition timing and advance…valve settings….fuel supply. This will then only leave the carbs and air system?
Just wondering…
deltarider:
Ignition always comes first in diagnosing. No matter what ignition you have, concentrate on a correct timing at full advance. I like mine to be just a tad more advanced than the outer mark. Then just accept the timing @ idle it will result in and live with it. Although I recommend using a strobe timing light, I myself don't do the actual adjusting dynamically. I set and then check using the timing light. If I need to readust, I first kill the engine, do an extra adjustment and check again. If necessary, I repeat this. This works best.
The position of the airscrew you have now, is a good starting point. A genuine Keihin one will look like shown below.
You're welcome anytime. I'm interested to see yours, as a 'K(0) 1975' is a rarity. ;)
Oddjob:
I've been talking to Mark Paris (Hondaman) a lot lately. Did you know BTW he's writing a book on the 500/550, the same type as he did for the 750. Anyway, he recommends removing the advance/retard springs and cutting a half turn off the end of them both, reshape to match original curl and refit. The stronger spring evidently changes the engine from its characteristic "switch ON, Switch OFF" torque sensation at 5000+ RPM to one of more linear response with more torque on hand all the time.
Off topic I know but very useful information which is sort of on topic in a way.
I'd second checking the valve timing before anything else, if it's one tooth out there is a great potential there for major damage. Might be a waste of time checking BUT it's worth it for peace of mind, if of course the engine ran just fine then you've clearly got it right but that's not the case here.
Sesman:
I’d love to see a physical representation of the spring modification. Any volunteers?
deltarider:
--- Quote from: Oddjob on February 25, 2022, 04:42:04 PM ---I've been talking to Mark Paris (Hondaman) a lot lately. Did you know BTW he's writing a book on the 500/550, the same type as he did for the 750. Anyway, he recommends removing the advance/retard springs and cutting a half turn off the end of them both, reshape to match original curl and refit. The stronger spring evidently changes the engine from its characteristic "switch ON, Switch OFF" torque sensation at 5000+ RPM to one of more linear response with more torque on hand all the time.
--- End quote ---
What makes you think this will be benificial? So far I haven't read one positive result, not one. One was frank enough to say he has experienced a negative effect... And I have followed it closely. Don't you think Honda was able - in a highly competive market - to design the best overall advance? It was never even clarified what advancer this was about: the Hitachi or the TEC? When you have sloppy springs, it may affect the idle somewhat. Then you can either tweak (no need to cut) the end of the spring or order new ones, about € 12,- a pair.
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