Topic: CB 400/4 ignition adjustment

[MDW]

I have been slowly getting the bike running well and had it at about  95%. Then I changed the screws that hold the points in place since the originals were completely chewed up. Now I wish I had just left them because the timing has gone haywire. I could get 1/4 firing pretty much on the F mark but only if the points gap was less than 0.3mm (spec). 2/3 I cannot seem to get anywhere close to the fire mark (I am using a 12v test light). I guess it must have something to do with the position of the points on the cam. Any recommendations what to do in this situation? Thanks

[newday777]

Where did you get the points from?

[M 750K6]

Assuming you only changed the points screws without touching the plate adjusters, it must be points gap. That's the variable in what you've touched. If the gap and timing were correct before you changed the points screws, then, if newly gapped points were right and the same as prìor to swapping the screws, 1 and 4 should still have been firing on F. Likewise, not having changed the relationship between 1/4 and 2/3 plates, 2 and 3 would automatically be correct.

I know points gap is meant to be basic maintenance, but I find I need to re-check a few times after a few rotations, before I'm happy I'm there. Also check your spring advance is operating smoothly and definitely returning to the stop.

[MDW]

M750K6 - The points are from David Silver.
newday777 - I follow your logic but I decided to check the timing and did that before checking the gaps (rookie error) so was moving the back plate etc. I spend over an hour trying to everything how it should be but didn't manage to. Now nothing is how it should be.  If I set the gaps then the firing is wrong. If I manually adjust to have the plugs just opening on the F mark then the gap isn't right at its widest point. I am not sure what my next step should be.

[Bodi]

The usual problem is getting the plate centred in the little nubs it sits into. Adjusting the 1-4 points is via rotating the entire plate, then the movable sub plate adjusts 2-3 once 1-4 is done and the main plate is locked down.
Some plates fit really snugly in those nubs. Some are pretty loose.
The plate does not have to be perfectly centred (ideal though) just unable to shift around other than rotating.
If my plate is loose I use shims to get the plate snugly set in place. Only a few though at each screw is usually needed, I take some shim stock and make a little piece maybe 1/4" by 1/2", punch a hole, then set it so the screw goes through that hole and a bit of the shim folds up against the nub (must be a better name for that). The plate being a few thou higher doesn't matter, the cam is considerably wider than what the points use.
Do not try to knock the nubs in with a hammer to snug up the plate! The metal is very brittle and knocking one off ruins your whole day.
Once the plate is secure, set your 1-4 gap at its widest opening to 0.0014" or very close, have the plate screws snug and rotate the entire plate to get opening at the 1-4 F mark, tighten the plate screws . Then set the 2-3 gap and use the movable sub plate to get the 2-3 points opening at their F mark.
If that isn't possible there is something wrong with your points. There are aftermarket sets that have the pivot point wrong and are an absolute nightmare to set... but DSS shouldn't be sending those.
I would use a strobe with engine running to make final adjustments, and personally I set to the advance mark at about 4000RPM. The bike will spend almost all riding time at the advance mark, so in my opinion that's the critical one. Idle timing is not critical, it's going to idle the same at a few degrees off. I also set the timing a bit advanced from the mark and use premium fuel but that is a bit risky, Honda set it up to not knock and melt pistons with typical fuel but there is a safety margin you can play within a bit.

[Deltarider]

[...] Adjusting the 1-4 points is via rotating the entire plate,

That's not correct. The 1-4 timing is done by rotating the entire plate, but prior to that the points gap can be set, by adjusting just the breakerpoints.
When a timing strobe is used, I advise not to adjust the timing with the engine running. Check using the strobe, then stop the engine, adjust, then check again with the engine running and if needed repeat these steps.
When a dwellmeter is used, you can adjust the points gap dynamically. Timing adjustments however are best done with the engine stopped. It's too much a hassle with this more or less loose plate, which moves about by the springloads the breakerpoints exercise.

[Bodi]

"That's not correct. The 1-4 timing is done by rotating the entire plate, but prior to that the points gap can be set, by adjusting just the breakerpoints."

"set your 1-4 gap at its widest opening to 0.0014" or very close, have the plate screws snug and rotate the entire plate to get opening at the 1-4 F mark"
Your point is...?

[Deltarider]

Your second sentence -  Adjusting the 1-4 points is via rotating the entire plate - was not correct.
Personal note: I haven't moved the plates in years. If you had a correct timing before, you can arrive there by adjusting the breakerpoints to the gap* they were before. It is unfortunate all manuals describe the full procedure, which is only needed when the plate has been removed. Normal maintenance is limited to just readjusting the gaps to as they were before and as a bonus you'll have the correct timing again. I mean, it's simple: the plates are fastened well and are not likely to move at all in use. 
* I've made it a habit, once I'm satisfied with the timing, to write down the dwell for 1+4 and 2+3 for future reference. Once the timing is of (the wear is at the points), I simply restore the dwell I had before and - tadaaa! - the timing is correct again. I didn't invent this practice myself, it was an old Honda mechanic who tought me this.

[M 750K6]

How are you measuring dwell?

[Deltarider]

Dwellmeter. Select the 8 cyl scale and aim at 23 - 24 degree. If it has only 4 cyl scale, aim for around 47 degrees (53% in Duty Cycle). Back then they were costly. Nowadays I advice to opt for an automotive one, if you need a DMM. Although I have a digital one, I prefer to use my old analogue one*. All dwellmeters - analogue as well as digital - offer tach reading too.
* Tip: look around for a second hand one on E-bay or similar platforms. You can find one for around $ 15 easily.

[M 750K6]

Thanks for the reply.

[MDW]

I had another go at fixing the problem at the weekend and the bike is now running well again except for vibrations around the 3-4K mark. Not sure what's causing that but at least I have something new to work on!