Topic: CB500 idle issue

[Honda-Rog]

Following my previous thread (http://forums.sohc4.net/index.php?topic=138656.msg1586053#msg1586053) about vacuum leaks - I've now checked, rechecked, reset, refurbished, replaced, almost everything fuel and electric-related in pursuit of the perfect idle - actually just one whichs stays steady will do.

I'm still not sure whether the erratic idle (c.1100 - 1300 rpm, occasionally dies altogether) is caused by a fuel or electrical issue.

Fuel - clean petcock, new hoses, all new jets etc. in carbs (from cruzinimage in Japan), and checked for any possible blockages - daylight clearly visible through all slow jets, new standard air filter, all rubbers etc checked for splits and wear, float heights checked umpteen times, needles on correct setting, air screws to 1.5 turns out, checked for vacuum leaks with WD40 around boots, . . .

Electric - coils are only a year old (primary resistances 5ohm, secondary resistances 16K and 17K - too high?), so are NGK plug caps (all read within 10% of 5Kohm), new non-resistor D7EA plugs, set to maximum gap, HM electronic ignition, wiring connections checked, recent points, reset gap, timing reset, auto advance working correctly, . . .

Other - Tappet clearances correctly set all round, but the nut behind the handlebars failed a recent sanity check  , . . .

Bike drives superbly once off idle, even more so with the new plugs. When it's cold or warm idle is pretty well perfect, around 1200 on the tach. When it's fully hot, the idle goes up and down, sounds very much like one cylinder is not firing at idle, and doesn't pick up cleanly on the throttle - in fact it sometimes dies if I'm too vigorous on the twist.

Several of you have been great in suggesting possible causes, but I've followed them all up and the problem persists.

Somebody, anybody, please help me crack this one - I've read all the other threads which seem to relate, and very often the cause turns out to be something I've already covered.

I need to decide whether it's fuel or electrical.

Thanks in anticipation!

Rog in Northampton, UK

[Honda-Rog]

OK, so I ripped out my aftermarket coils (nasty things, with poor leads), and put in a used set of original coils. Result - one perfectly idling machine! Yes, I know I could have corrected a poor connection somewhere along the line, but I'd already gone through those, and although coils are supposedly pretty reliable, in this case I'm sure there was an issue with one of them - and they're only 18 months old.

No doubt there's a few of you who are sick of my ramblings, so I'll try not to have / cause any more problems for a while. Time to ride, before the great British weather turns to autumn and winter! But, hey, we've had a good summer, lots of sun and good (for the UK) temperatures, around mid-20s celsius.

Again thanks to everyone who's tried to help me. Safe riding!

[calj737]

Brilliant! Delighted that you solved the problem-

[Honda-Rog]

Cheers Calj737.

[Vinhead1957]

Did you do any comparison to the good coils ?   Check the bad ones for splits or intermittent wires?