Cleaning the Advance Mechanism | Honda CB750 Ignition Timing | Motorcycle Project | Part 27

Cleaning the Advance Mechanism | Honda CB750 Ignition Timing | Motorcycle Project | Part 27
In this episode, I clean the advance retard mechanism on my CB750 project bike. I am building this bike to be a road-going runner, not a full restoration.
Items I used in this video.
Holts Electrical Contact Cleaner: ebay.us/wKVST2
Graphite Oil Spray: ebay.us/Dal2tH
JIS Screwdriver set: ebay.us/xJj4ad
The advance and retard mechanism is a simple pair of weights controlled by springs behind the points plate. As the weights move out when the engine revs increase the cam that opens the points moves clockwise by a few degrees so that the points start to open earlier.
Petrol and air burns at the same rate no matter what speed the engine is going at. To make sure that the maximum power is given from the petrol and air burning, it is set alight so that it is giving the most power just after the piston reaches top dead centre. As the revs of the engine increase, it needs to happen sooner so that the maximum power is maintained. If it was set that way all of the time then the engine would kickback when starting.
On a mechanical system like this the timing is advanced at around 2000 revs then stays at the same point for any higher speeds. With a more modern electronic system, the advance can be tailored to any speed that the engine is running at. This is one of the reasons modern ignition systems give better fuel efficiency and more power than older systems.
I simply clean the system to make sure it is free using some electrical contact spray. I then give it a light misting of graphite oil to give it a little lubrication for the future. I could have used any light oil, but using the graphite oil should provide lubrication for longer.
After I had completed this the engine ran much better giving more power and generally feeling much livelier.
For more helpful how-to guides and restoration project logs, visit our blog: www.spannerras...
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[@rodofsteel6662]

I have been looking for ever. My bike gets warm and as soon as I stop and pull In the clutch it’s 4,000 rpm and then slowly goes down. As soon as I take off it’s fine, it shifts fine and runs fine. I believe this is my problem.

[@SPANNERRASH]

I wouldn't think that is a advance problem. I would check the throttle cable first, it could be sticking slightly, it doesn't take a lot to keep the revs up. Then I would check for air leaks on the inlet side, maybe a split in one of the manifold rubbers or one of the clamps loose. I hope this helps you find your problem.

[@jamesrichardson1901]

I had an airhead BMW and could tell when the gap needed adjusting by the way it ran. Have you thought about converting to electronic ignition? Surely there's a kit out there.

[@SPANNERRASH]

Ahh there's definitely CB750 electronic ignition kits out there, and to be honest I am planning to put one in at some point. But there's a certain enjoyment to getting these old points ignitions set up just right, so as long as the CB750 runs well, I won't rush to do the upgrade to electronic.

[@Kpdadon87]

If I cracked the points case can it be replaced

[@SPANNERRASH]

I'm not sure what you mean by points case. If you are saying part of the crankcase then that would be quite a big issue. Anything can be repaired and replaced, it is just the cost and time involved that would stop you. If you have damaged the crankcase then depending on what has happened to it you may be able get it repaired in situ, otherwise it is a full engine strip. Good luck.

[@korkie6666]

What tool are you using? The one with a light? Does it adjust the top dead center? Is that just a circuit tester?

[@SPANNERRASH]

It is a circuit tester! You take the timing marks from the backing plate of the points for TDC. If you clip the circuit tester to the spring on the points, and to a ground then it lights up when the points open. I hope that helps.

[@josedinis1205]

you forgot to grease the came.

[@SPANNERRASH]

Good point, must mention it next time.