SOHC.co.uk Forums > CB750

Hesitation after @ 4500 rpm

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Oggers:
Not a Honda - but I feel you gents may be able to point me in right direction as the solution may be similar for CBs . I have another bike - 78 Kawasaki KZ650 - which has performed wonderfully since restoration a year or so ago. I took it out on Friday and it ran beautifully. Saturday took it out on another spin, but this time filled it up with super unleaded as normal. After that, bike rans fine until you give it some throttle at @ 4500 rpm and it hesitates - somewhat alarmingly lurching as it does so. It tries to go, but hestitates again. Very erratic, very hesistant, will not go above 4500. Below 4500 it seems OK - ish....

Clearly I have though about rubbish in the tank being disturbed when filling up, and then finding its way to the carbs. I took the tank filter off - very clean, and the extra in-line filter between petcock and carbs looks fine and clean. Cleaned plugs - all OK, checked gap - OK, cleaned air screw needles - all OK, fuel line blown through, vacuum take off to petcock is OK, Auto advance lubed up, all seems free moving.

Taking the carbs off and cleaning jets etc. is a royal pain. Has anyone got any other suggestions that I could easily do, and do you feel I am on the right track with the root cause? - rubbish in the carbs bascially. Deeply annoying after it was running so well!

K2-K6:
Can you give it just a little choke as it hesitates at 4500 rpm ? It's just to see if being a little richer can alllow it to increase revs and give a pointer as to what it's doing.
If it doesn't help, it's possibly not fuel.

K2-K6:
Another thought about this, someone here had a pattern, I think, fuel tap on a Kawasaki that was restricting the fuel flow such that it wouldn't rev as carb float bowls depleted level during a run.

Worthwhile checking for straight flow from the tank into a pot to see what you have there.

Lobo:
I’d have thought (significant) carbs issues would appear gradually over time given your filters are clean. And given the problem has appeared in an instant, surely more likely something obvious…. Plugs, coils, condenser, faulty power supply to the coils etc (if not fuel supply.)

Certainly I wouldn’t be taking the bloody carbs off until all the obvious ruled out.

Oddjob:
Have you checked the fuel cap vent is unblocked?

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