Judge my CB550F2 1977 idling

[McCabe-Thiele (Ted)]

This is the direct link to the boots!

https://www.ebay.de/itm/361837356740

Ok so have you checked old against new,

[Oddjob]

Any chance you fitted them back to front? Easy done

[alexdecker]

I've used the right boots for the intake. They are easy to differentiate, as they have the lips that go into the airbox. Unfortunately I can't measure them up against the old ones, as I chucked them when the new ones was installed in a pre-mature celebratory moment of relief of finally having done this task, as un- and reinstalling the carbs is such a pita! 🙁

[Oddjob]

Forgot to mention, the inner 2 are sort of handed. The originals have a small tab which sticks out of the part that goes into the plenum chamber. These fit between 2 bumps on the chamber, it's to ensure you get the correct orientation. They face inwards towards each other.  Plus you can remove the boots in situ. Just unbolt the airbox and slide in backwards. You can then refit them with a little difficulty but it is doable.

[alexdecker]

Okay, this story is slowly unfolding to a grim nightmare. Got the boots fixed on all 4 intakes and exhausts, but now 2 & 3 are not firing at all.

Here is what I have done so far:

• When I had the carburetor out, I cleaned it, before putting it in with new boots (just carb cleaner, but had the top lid off and the float bowls)
• I replaced the points with new original Honda points
• I then set cam chain, valves (kept them to the looser side of around 0,08 mm intake and 0.1 mm exhaust). I then set timing.

Measured the coils and they measure a 3.2 ohm resistance each. The points are getting power. The timing is dead on. I got spark on all the plugs.

What on earth could cause 2 & 3 to just set out all of a sudden?

- Alex

[deltarider]

Do contactbreaker 2+3 connectors accidently make contact to the plate? Check carefully that these forked connectors are well isolated from the plate.

[Oddjob]

Check the connectors near the rear brake light switch. You may have disturbed one. Also check the connectors near the coils. Just done a z1000 where 2-3 weren’t firing, it was the coil. Yours however is more likely to be an electrical connection issue.

[exvalvesetdabbler]

Pull the plug cap off 2/3, connect up a spare spark plug and lay it on the engine to earth it.

Turn the crank so points 2/3 closed,
Ignition on.
Open close the points with your thumb nail, spark?

Do the same with volt meter across the points, 12v open , 0 volt closed.

Where the wires connect to the points, are the insulators in the right place or have you grounded them to the points base?

Regard
Dave

[Oddjob]

He has mentioned that he has a spark on all 4 plugs. You haven’t made the mistake of mixing up the ht leads have you? You wouldn’t be the first tbh. That normally means 2 and 4 don’t work though not 2 and 3. The middle 2 cylinders don’t share a fuel feed so it can’t be that. I wonder if the coil is breaking down under load.

[exvalvesetdabbler]

Floats stuck closed?  Any fuel in the bowls?

[alexdecker]

Oh my god, Deltarider was right on the money! Rechecked everything and was slowly going insane. After reading his comment, I was like "surely that can't be it". Went down, one of the wires on the second point had slightly moved towards the plate and was making the tiniest of contact. Cleared it, started the bike, and it went ahead and puuuuuurred like a kitten (albeit a kitten who needed a vacuum sync), firing on all four again.

Shit, these old bikes. It can be anything, but sometimes it's just the tiniest stupidest of things.

We are back! I vacuum-synced it today. Will be back with an idle video tomorrow and ask for comparison with the old one. To my ears, it sounds beautiful now. Also it revs so cleanly.

- Alex

[deltarider]

It is often missed, when it occurs intermittent.

[alexdecker]

Okay, here is the original idle: https://youtube.com/shorts/xxPyy_B_-Uw?is=KRgiZOVffDpVbALb

And here is the idle now, after new boots and a full service, finished off with a vacuum sync. Best I could do: https://youtube.com/shorts/o2YUFxFuxzQ?is=LzYdFp6CxF26aIb0

Does this sound fine to you?

[deltarider]

It's fine now. Go for a ride, in town, minor roads and highway. Have it run at a maintained 6000 rpm or higher for some time to burn of all the carbon caused by all this idling. You'll be surprised.

[alexdecker]

It's fine now. Go for a ride, in town, minor roads and highway. Have it run at a maintained 6000 rpm or higher for some time to burn of all the carbon caused by all this idling. You'll be surprised.

Ah, interesting! Theoretically, what can happen with the build up of carbon? I never really thought about that (like so many other things obviously)…