Topic: 1977 cb550k backfiring on ignition

[Fortune]

As the title says, I'm having trouble getting up and running at the moment. Bone stock cb550 - stock airbox, stock pipes, stock jets. When I use electric/kick the bike starts like it's going to idle for a few seconds but feels like its waiting to die as soon as i drop throttle too low. If I give it a little gas during either, it will sputter like it isn't getting gas (it definitely is as I've flooded the carbs and had to drain them while doing this) ((running clear gas line so i can double confirm))

If I keep at this for a few seconds, it will start backfiring inconsistently, and send me to the kitchen for another beer.

I've since replaced all condensers and points, done timing, set valves, run gas through the carbs to see how the gas looks (crystal clear), unsuccessfully searched for vacuum leaks, and ultrasonic cleaned the carbs.

What could cause ignition to be so abhorrently off despite everything appearing perfect? Is this... an air issue?


I'm out of beer.



Love you guys 🫠

[Cruiser]

Have you checked the static timing with a light just to be sure its firing at the exact time it should be firing? If so, check with a stroboscope on all leads.

What was the initial reason to do all the work you've done? Has it been sitting for a long time? Did it run good before?
Are the floats at the correct position? Did you check all needles and jets?

For me it sounds like spark issue (timing or actual spark).

I assume no rebuild work was done to the top half (camshaft hasn't been of the bike?)? You can always manually check if the valves open/close on the expected moment.

[calj737]

Confirm your coils are wired to the correct pairs of cylinders too. One coil for 1/4, the other for 2/3. These need to match to the Blue/Yellow wires.

Once you get it fired and stable, that’s when you need to vacuum synch the carbs and set the idle.

[Fortune]

What was the initial reason to do all the work you've done? Has it been sitting for a long time? Did it run good before?
Are the floats at the correct position? Did you check all needles and jets?

For me it sounds like spark issue (timing or actual spark).

It was running and ridden every day for months prior then suddenly encountered this issue. After reading this I triple checked coils and timing and realized one of the wires had torn from the coil! I replaced with a new set all around and... backfiring has (almost) ceased! It's far more infrequent, however it seems like cylinders 2 and 3 aren't firing correctly now...

Endless journey here!

[Deltarider]

First check the ignition.
Step 1. Make sure the connectors at the 2+3 breakerpoints do not ground to the crosshead and/or the plate. It happens that after assembling, they can easily touch ground and when that contact is intermittent, it is often overlooked.
Step 2. Check for arcing. a) From plugcaps to the head (best seen in the dark) and b) somewhere at the breakerpoints. OEM breakerpoints and condensers? Plugcaps and their resistance OK?