Topic: Advance mechanism springs

[Big Bob]

I searched and came up empty.

Bike in question is a 1972 CB 500.  I suspect the timing advance mechanism springs are shot.  Honda lists the whole advance mechanism as one part.  Anyone have any ideas on a source?

Chasing ignition gremlins.  Ugh.

Also - is there a good test for condensors besides charging them up and tossing them to your buddy?

[Bodi]

The springs just set the advance rpm. This is not a critical setting unless it gets severely wacky. You can check it very easily, with a strobe timing light. The timing pointer should be quite steady under the strobe at or near the T mark. As rpm rises, it gets a bit shaky as it creeps towards the advance (unlabelled) timing mark. By 2500 rpm or so it should be steady at the advance mark and not move with more revs.
You should set the timing at the advance mark. Too much advance can damage the engine, too little gives poor performance. The advance angle is a bit variable, and the exact amount of ignition retard at idle is not very important - especially compared to how important the right ignition timing at normal riding rpm is.

[Steve F]

The springs just set the advance rpm. This is not a critical setting unless it gets severely wacky. You can check it very easily, with a strobe timing light. The timing pointer should be quite steady under the strobe at or near the T mark. As rpm rises, it gets a bit shaky as it creeps towards the advance (unlabelled) timing mark. By 2500 rpm or so it should be steady at the advance mark and not move with more revs.
You should set the timing at the advance mark. Too much advance can damage the engine, too little gives poor performance. The advance angle is a bit variable, and the exact amount of ignition retard at idle is not very important - especially compared to how important the right ignition timing at normal riding rpm is.

Yes...but do you know of a source for new springs that are the correct tension and length?  Does anyone know what the specs are for those springs when new?

[mystic_1]

The timing pointer should be quite steady under the strobe at or near the T mark.

Shouldn't that be, "at or near the F mark"?


mystic_1

[Spanner 1]

Disagree with Bodi.... first @ idle or static timing spark spark needs to be @ F mark, as Mystic points-out,  the two '' max advance marks are just for reference...i.e. the advance is set as the two arms 'fly' out with increased rpm until they hit their stops. So advance marks only prove the advance mech. is turning. Stronger or weaker springs would only have effect on what rpm the advance starts to happen and what rpm advance is completed...,,Honda says advance should start at 1,150rpm ( right from idle ) and be 'all the way' at 2,500rpm.
I'm not aware the springs go weak...easy to check, if weak then full advance marks will appaer well under 2,500rpm. Much more common is stuck/sticky advance unit, take apart ,clean' lube and re-time......

[Bodi]

True, it's the F mark that is roughly static or idle timing. T is top dead centre. Dumb mistake, sorry.
You still want to set actual timing at higher rpm to the unlabelled advance mark. The static/idle mark is accurate if the advance mechanism is exactly correct, but wear will make it advance a bit more. A few degrees later won't make any difference at idle. A few degrees too much advance could cause detonation and piston damage at high rpm.
This isn't really critical with stock timing, but it is common to advance the ignition slightly to get better performance. Honda has the advance set conservatively - to avoid detonation and melted pistons. Going a few degrees more advance makes a difference in mid and top end power: overdo it and you're in trouble. If you do this it is critical to adjust the ignition timing at higher rpm and full advance.

[Spanner 1]

Changing the static/idle timing away from the F mark actually achieves nothing....the advance mech. will still be at max. advance due
to centrifical energy by 2,500 rpm..... all you have done is move the advance ' curve' away from the Honda calculations and automatically deciede your engineering is better for the motor.......IMO

[Deltarider]

This isn't really critical with stock timing, but it is common to advance the ignition slightly to get better performance. Honda has the advance set conservatively - to avoid detonation and melted pistons. Going a few degrees more advance makes a difference in mid and top end power: overdo it and you're in trouble. If you do this it is critical to adjust the ignition timing at higher rpm and full advance.

True. Driveability improves with a little extra advance.

Much more common is stuck/sticky advance unit, take apart ,clean' lube and re-time......

True.
Nachfertigungen (imitations) of these springs are available for members of the German cbfourclub (Clubshop/Harald Dietz). You might send them an e-mail to find out where they get them from. (shop_@cbfourclub.de)

[Deltarider]

You might send them an e-mail to find out where they get them from. (shop_@cbfourclub.de)

.
Well, I just did and will report back.