Topic: Ports on 1979 Honda CB650 carb

[jaffyrider]

Hello,

New to the forum here, so thanks for having me! I've downloaded some manuals in the past which have been very helpful.

I'm currently having some carb troubles. I have a 1979 Honda CB650 which tends to bog when I increase the throttle from idle. The response is good at higher RPM's. It's just at lower RPM's when I slowly or quickly increase the throttle, the engine hesitates and wants to die. I've taken the carbs off again to have another look. My question is, in the picture below, what are those ports (labeled A,B,C)? What do they do and where do they go? That is, what is their purpose and if I blow compressed air/carb cleaner through them where will it end up? This is a view of the #2 carb but all three ports are on every carb. Thanks again, and looking forward to the response.

Best,

Jaffy

[Mr. Mike]

Jaffy,

The carbs should be disassembled to clear those passages out, and a thorough cleaning will be in order after that. I can’t identify with certainty all of those orifices but you should not just blow them in.

Second, edit “D” is the accelerator pump. When twisting the throttle from idle, a brief squirt of gas shoots out of brass nozzle tube marked “E”.

Try twisting the throttle quickly while looking at each nozzle and you should see a steam of gas squirt out. It appears you’ve got your carbs on a bench of sorts, so to test the pump, you’ll have to get gas into that #2 carb to see if any of them squirt fuel.
Hope this helps.

[TwoTired]

A, B, and C apear to be air jets.
In similar carbs they feed air to the emulsion tubes associated with the main and slow jet fuel metering systems.

I'm not sure of the third one.  Maybe it feeds the anti backfire diaphrams during fuel enrichment on decelleration.  I'm not certain your carbs have these, though.

Your reported symptoms of poor throttle response are consistent with a faulty accelerator pump system, the pump being located at the bottom of the bowl (D) on the second carb. The brass post at the carb mouth entrance is the squirt jet facing into the carb.  Upon throttle twist these 4 posts should squirt a pretty strong steam into the carb throat.