1969 CA77 runs erratically

[quidger]

https://www.dropbox.com/scl/fi/r7brfozc ... 3mwk7&dl=0

https://www.dropbox.com/scl/fi/l8w2bwn5 ... q0bfv&dl=0

Here’s a link to videos of bike running.

Coil tested good. Installed new spark plug s and boots and reset the timing. Carburetor cleaned and ultrasonic cleaned umpteen times.Compression 125/130. Valves adjusted. Minimal smoke from exhausts. Some black , drier soot on plugs.
Bike starts on the first kick every time and the engine runs normally for a short period of time, 4-5 minutes . Slowly the bike loses its idle and then it dies. I tried to adjust the idle screw when it was running to increase the idle and it had little effect on it.When it gets warmed up after five or so minutes of running the bike simply has a decreased idle and dies.
Any thoughts would be appreciated.

[Tim Allman]

Things like this are often hard to diagnose but here's one idea.

The throttle cable needs to be really clean and free to move. If it sticks and holds the slide a bit above the idle speed screw it can slowly move and drop the idle speed. WD-40 is a convenient cleaner to inject at the top and catch at the bottom. I use light oil such as 3 in 1 to lubricate the cables.

In the videos the idle speed seems a bit slow. I know you don't have a tachometer so you might want to get a hand held one. (That's what the dimple in the bolt that holds the rotor on the right side of the crankshaft is for.) The recommendation for my CB77 is about 1000 RPM. I doubt yours differs much.

[Nick]

1. Did you confirm that the pilot jet is clear? That is, did you remove it from the carb, hold it up to a light and confirm that you can see through it. If you can't, remove a single strand of copper wire from a piece of wire and used it to clear the blockage. "I cleaned the carb," doesn't mean much if you haven't visually confirmed that all jets are clear. Ideally, you also want to blow the carb out with compressed air immediately after cleaning. Also confirm that the passageway for the idle circuit is clear.
2. Remove the float needle seat from the carb and check that there is no accumulated dirt, etc. in there.
3 Check float level
4. Disconnect the fuel line and confirm good fuel flow from the petcock.
5. Ensure that the fuel cap breather is clear. Or, loosen the fuel cap if there's not too much fuel in the tank.

6. If adjusting the air screw has no effect on how the bike runs, it means the idle air circuit is plugged. Starting point is one and one-half turns out from fully bottomed, with about a half turn in either direction for best running.

[Michael Stoic]

To pile on, in good company, I would add: check the needle position in the slide and the actual size of the carb jet. Make sure both are in spec. Also, you have a nicely painted frame, but the ground connection might be affected. During testing, I'd put some additional temporary ground wires from the coil and battery to the motor.

Mike Stoic
honda305.com/dream/registry