Topic: Hesitates Off Idle

[Vintageguy]

Have a 1978 CB750F Super Sport. Usually starts in 1 or 2 cold kicks and runs like a champ through the gears and cruising at speed. However, coming off idle she will hesitate a bit until the rpm's come up above about 1,000. I have heard the the EPA (then in infancy) gave Honda a hard time back in the day concerning their idle circuit smog numbers. Do all these bikes run lean in the idle circuit, or is it something else? BTW; Stock jets. Thanks for any/all responses. 

[scottly]

Your carbs have an accelerator pump that enriches the mixture when the throttle is opened. You might want to make sure it's working properly.

[Pbeattie89]

I did a quick search on stock idle speeds for your bike, and I came across a thread saying that these bikes prefer an idle speed around 1200 rpm. Checking carb synchronization, mixture screws and accelerator pump function will also help the transient response coming off of idle.


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[bryanj]

Your idle is too low

[HondaMan]

The 2 things I know will cause this with those PD41 carbs is:
1. The accelerator pump's diaphragm is old and got stiff from the years of MTBE-laced fuels trying to wreck it (they almost worked...).
2. The teeny-tiny O-rings on the tips of those idle-mix adjust screws are hard and shrunken (from the same cause) and now they will not adjust according to 'normal' settings. Instead they usually need to be set 1/8 to 1/4 turn more closed to make the same mixture as at normal settings.

Note: if you go to replace those idle-mix O-rings, use the ones found in carb kits. DON'T replace the brass with that found in many of those kits. The brass doesn't "wear out" in these carbs until well over 100,000 miles (mine finally showed SOME wear at 120k+ miles) and 100% of aftermarket brass parts for the PD carbs is dead wrong. It will usually make the bike hard to start, nearly impossible to idle, and run very, very lean.

The O-ring kits from PartsNmore for the K7/8 bikes work fine: this is their part #48-1995. It includes a proper O-ring for the idle-mix screw.