Topic: Spark advancer '73 CB750 - Help!

[Mark K]

Rebuilding the engine, removed the spark advancer, did not remove the tiny shaft. Do I need to replace the tiny o-ring behind the tiny shaft?

Also, does the collared shaft go over the spark advancer and if so, how does it fit? When I disassembled the engine a year or more ago, I don't remember removing the collared shaft and I don't see it in the parts diagram.

[WideAWAKE]

I can’t comment to the little o ring.

But to get that collar back on you basically spread the weights and align the notches of the collar so it slips down under the weights. There should be a very thin washer that sits between the advance body and the collar.

If it was mine, I’d complete disassemble it, clean it, oil the pivot posts and the collar.

You will notice there is a small mark on the collar, that align with the hole on the advance body. If you put it on the opposite way, your moped will be pedals only haha

[Bigmant]

+1 to the above

Totally agree with taking apart and lubricating everything you can. You’ll be surprised with the results. You can actually feel it even when it’s off the bike.

[Mark K]

Thanks for your help.

[MauiK3]

In all likelihood your springs are weak due to age and heat. This causes early advance, and poor running.
Tell me about it!
Hondaman has discussed this at length, get his book pronto! It’s my savior.
On at least one spring, cut off one winding and re-form the loop.
When the motor is running check total advance with a timing light. About 2500-3000 rpm for full advance

Link
http://forums.sohc4.net/index.php?topic=131339.0

[70CB750]

^^^ That^^^

I shortened advancer springs on Dorothy and it made a huge difference. 

[madmtnmotors]

Make sure you get the "collar" (A.K.A. points cam) oriented correctly. The procedure for indexing this points cam properly can be found in the shop manual. Getting the points cam oriented properly is necessary for proper ignition function. 

[PeWe]

Both my CB750 got both springs cut. My K6 advancer had a huge play with full advance kicking in too early. Not possible to adjust.

Found thread about cutting springs were Hondaman  recommended it.
That solved it. I usually adjust F to line up at idle, full advance happen at 2600-2700 rpm.
I like smooth running engine at take offs and at low rpm.

Here my first cut of the springs solving the problem.
http://forums.sohc4.net/index.php/topic,131339.msg1464986.html#msg1464986