Cold start trouble

C

CJM37

New Member
Have a Honda 78 CB750 that starts great after it’s warm but is almost impossible to start cold. Carbs rebuilt and adjust. Top end rebuilt. Any ideas on what the problem might be. Any help is appreciated.


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The '78 has an accelerator pump, I would put my money on either a pinhole in the accelerator pump diaphragm or something like a stuck choke. Start there, but could also be that your mixture is off or possibly valves too tight?
 
That pump circuit notoriously clogs when they've sat for a while, and it's very difficult to clean.
 
coyote13 said:
The '78 has an accelerator pump, I would put my money on either a pinhole in the accelerator pump diaphragm or something like a stuck choke. Start there, but could also be that your mixture is off or possibly valves too tight?
Click to expand...
I bet you are right I rebuilt the pump but didn’t clean out that pinhole. Thanks a lot I will try that if I can figure out the best way to clean it


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Cold start trouble

Cleaning the pump won’t do you any good if the circuit is clogged. You should’ve checked for squirt on all four holes if you had them apart already. It’s very common for people to clean these PD carbs, but not get the pump circuit clean. Also, while they’re out did you check the timing of the squirt? Fortunately, these carbs will squirt through the choke plates.


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irk miller said:
Cleaning the pump won’t do you any good if the circuit is clogged. You should’ve checked for squirt on all four holes if you had them apart already. It’s very common for people to clean these PD carbs, but not get the pump circuit clean. Also, while they’re out did you check the timing of the squirt? Fortunately, these carbs will squirt through the choke plates.


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Click to expand...
Thanks a lot. Pulled the little spring and ball out of the accelerator pump cleaned that and cleaned the circuit. Problem solved.


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