Topic: My CB750a only runs well with the choke on. Ideas?

[Hambone]

My 1977 CB750a only runs well when I pull out on the choke. It runs rough and stalls when I release it. It is an automatic model, does that sound like the accelerator pump diaphram? The carbs are super clean, I just need to find out where to start.

[CB500_k2]

I had the same problem with my CB500 when I was bringing her back to life.  I had completely cleaned the carbs, compression was good, ignition timing perfect but it would only run with the choke engaged.  After much exasperation and multiple carb removals I raised the fuel levels in the carbs by raising float height and she has run perfectly ever since.  I measured the actual liquid level with a plastic tube connected to a modified drain screw.  I set the level 2 mm below the gasket.

[Gordon]

Is the air filter installed?

[Spanner 1]

The carbs on the A are very dependent on the acc. pump at anything above idle...the squirt of fuel increases the rpm enough for the main-jet to take over..blah, blah...!
the 'pump' circuit does not effect idle tho', so i'd be looking at float level ( as previous post) and low speed jets, did you pull 'em out and clean them and flush their air passage from the carb throat ?

[Hambone]

Thanks! I'll get them off. and check the float levels. I have only had the bike a couple of days but I need to get this worked out.

[JS550]

Is the tank clean? I had my carbs off a lot without realizing that the sh!t in my tank was clogging my jets up.

[Hambone]

Thanks for the help guys!