Topic: Idle Information

[Vintageguy]

My 1978 CB750 F runs well in all ranges, but does not come off idle well. There is a "catch" around 1500 rpm that does not appear anywhere else. The bike has the original jets in the original carbs. The bike is a 1 PO, 9,000 mile survivor from California and is about 95% original or OEM. I have been provided various suggestions to remedy this condition including replacing idle jets, or replacing main jets. Does anyone here know from previous experience which is correct (or both?) before I dive in? Thanks to all responding.

[ekpent]

 I think those have what are called "pumper" carbs and possibly that circuit is clogged or the pumper membrane is old and not working right. Supposedly with the airbox off gas should squirt and be visible out a little orifice in the carb mouth when the throttle is twisted open. Easy enough to test while troubleshooting.

[TwoTired]

Stock air box filter and exhaust?  That's what the carbs were originally tuned for.

You sure the accelerator pump is doing it's proper job?  It should shoot gas 4-5 inches into each carb throat when you twist the grip.

Cheers,