1980 Suzuki GSX400 Choke issues

[xxenzor]

I’ve disassembled and cleaned the carb on my 1980 Suzuki GSX400 four times now. The bike runs and rides well, but I’m having some trouble with starting. If I have the choke even slightly on (1/4 on), it struggles to start and will stall unless I give it constant throttle. I can usually get it started by giving it throttle with the choke off, and after 10-15 seconds of throttle, it will idle.

I’ve inspected the choke plungers, replaced the O-rings, and ensured they move smoothly. Sometimes, the idle behaves oddly. I’ll set it around 1100 RPM, but after riding for a few minutes, the idle increases to around 1500 RPM. I’ve synced the carbs and adjusted the air screws using the methods on BikeCliff. I’ve also ensured the airbox is seated properly on the carb and sprayed starter fluid on the boots with no changes in RPM.

Any ideas on what might be causing these issues?

[tom203]

“…can usually get it started by giving it throttle with the choke off, and after 10-15 seconds of throttle, it will idle.“

so it idles nicely after this startup hesitation ? About how long is starter motor cranking with 1/4 “choke” applied?

[Nessism]

Did you clean the choke passage through the float bowl? Shoot carb cleaner though the passage to make sure it's open.

Did you remove the choke plungers and make sure they move smoothly in the carb passage?

With the choke plunger removed, stick the spray tube for a can of carb cleaner into the small hole at the bottom of the passage and shoot, visually verifying the spray comes out the choke tube in the float bowl? Spray should come out both the end of the brass tube, but also shoot out sideways near the gasket surface.

[zed1015]

Having to give it throttle ( more air ) with the choke ( enrichener ) closed indicates it is getting too much fuel.