Hesitating at speed~

[Spitfire]

It's my very loved 1990 k75- rides well except for the hesitation when up shifting-I have to almost "catch the bike up" with the throttle... and recently a very noisy fuel pump(?) Just emptied and cleaned the tank- maybe an air bubble in the fuel system- would that match the symptoms? Should I be able to hear the fuel pump anyways?

[mystic red]

and recently a very noisy fuel pump(?)

So it's more noisy than it used to be?

[johnny]

catch the bike up... slipping clutch most prevalent in higher gears whacking the throttle...

j o

[Spitfire]

Yes it's a bit noisier- I don't remember being able to hear the fuel pump through my helmet. I did just clean the tank- maybe the pump is still priming(?) :dunno2:

[JamesInCA]

I can just hear mine faintly through the helmet, just a subtle but clear, constant whine or whirr from the tank. Does your noise sound different?

It would seem low or inconsistent fuel pressure might cause hesitation, no?  Harbor Freight has a relatively cheap fuel injection pressure gauge setup. (If you get one, be sure you get the one for fuel-injected engines, not the carb one. Completely different measurement range.)

Everything should be primed and pressurized once the engine is running. Maybe it'll be rough for the first few seconds running. But when I've had the tank and/or fuel hoses off, it's usually just cranky about starting - once it's started, it's fine.

[Scott_]

Last time the fuel filter was changed?