Topic: Ignition way off when timing

[cfeste]

Hi!

Posting here even though it's a CB750A (1977), since I am guessing ignition issues are the same.

When checking/setting the ignition timing, idle fire seems to be where the 2500-3000 RPMs should be. I cannot adjust the points plate far enough for it to fire on the 1-4 F mark where I think it should be on idle. However, the bike idles just fine. Any idea what this can be?

Apart from idling OK, the bike runs horribly on mid to full throttle. It just feels "dead", but with no popping or other sounds indication (to me at least) if it's a timing issue, running lean or rich etc.

Any input appreciated!

BTW: I do plan on getting a Pamco or Dyna-S ignition, but want to give it another go with the original setup. Carbs are "semi clean", and could probably need a proper clean and rebuild parts.

[MoMo]

Points should fire at the F mark, which is 1200 rpm.  Not sure what you mean by this "idle fire seems to be where the 2500-3000 RPMs should be"-that should be where the advance is.  ...Larrry

[cfeste]

Hi! Following the shop manual, I am using a timing lamp to check at idle, which should be +/-950 rpm's. At that RPM it seems to fire where the advance should be, around the two marks to the right of the T-F-1-4 marks. And if I rev it up, there are no marks where it fires, so the whole thing seems to be way too early. Which I thought would lead to poor idling, popping etc. (or not idling at all). Experience with cars, not with bikes, this is my first CB!

[MoMo]

What is your point gap?  I would put the main point plate back so the retaining screw is in the middle, same with the 2/3 plate.  Remove a plug so you can rotate the motor with little resistance. Set 1/4 gap first, between .012 to .016, with the post that holds the spring showing in the window-that should be where the points are at the widest gap.  Then rotate crank till the post for 2/3 shows in the window and set that gap.  Then use the timing light to set 1/4 so that it fires at the F and advances between the two advance marks-you'll rotate the main backing plate to achieve that.  Then switch the timing light lead to either 2 or 3 and use that separate backing plate to get the correct fire and advance for 2/3...Larry

[Davez134]

Also, if you set your idle (using idle adjustment screw on carbs) before you did points gaps, timing etc, you will be chasing your tail. For example if your timing advance was off and you adjusted your idle screw to the idle speed you want, it may only be able to fire while advanced but die out before you can get the timing marks positioned correctly.  Important that valves are adjusted, points plate and points are set as MoMo states, then mess with idle speed on carbs.

[cfeste]

I am not sure what previous owners may have done, but I did adjust the valves and point gaps, while the idle rpm's stayed the same. Then tried setting the ignition. But of course I could go over it in that order again, just to make sure it's all set.

The retaining screw is in the middle, and it actually has less effect than I am used to when rotating it. Also not sure what you mean by "main point plate" and "2/3 plate". There is only one plate to rotate.

I am thinking maybe the points/condensors/coils are bad.

Is it a bad sign that the engine is really easy to turn with all plugs in place? Low compression maybe? Could that manifest itself with the symptoms I am having?

[MoMo]

I am assuming the auto has the same point system as all other 750s, in that there is a large plate that holds both set of points and a smaller plate mounted on top of the large backing plate and holds the points for 2/3.  It has been over 35 years since I worked on an auto...Larry

[lucky]

Stop using the timing light.
Just static time it and make sure the advance unit is not all rusted.

It will run perfect.

[HondaMan]

Hi!

Posting here even though it's a CB750A (1977), since I am guessing ignition issues are the same.

When checking/setting the ignition timing, idle fire seems to be where the 2500-3000 RPMs should be. I cannot adjust the points plate far enough for it to fire on the 1-4 F mark where I think it should be on idle. However, the bike idles just fine. Any idea what this can be?

Apart from idling OK, the bike runs horribly on mid to full throttle. It just feels "dead", but with no popping or other sounds indication (to me at least) if it's a timing issue, running lean or rich etc.

Any input appreciated!

BTW: I do plan on getting a Pamco or Dyna-S ignition, but want to give it another go with the original setup. Carbs are "semi clean", and could probably need a proper clean and rebuild parts.

One very likely possibility: if the points are the Daiichi brand, they can not be adjusted properly. They are mechanically incorrect. Look closely at the points base, see it there is a tiny 3-leafed plant-like emblem that resembles a clover with pointed leafs: if so, the points are Daiichi brand. The only good way to fix those is to replace them. Honda still sells the very best, the TEC brand points, for these bikes. They time up in the first try, every time. Make sure the whole baseplate is also TEC, or at least Hitachi brand. The Daiichi baseplate is very loose in the mounts, which makes the timing problems even worse.