Engine bogs down low when not really really hot

I have a kz 750 H4. She's running - and well, generally. She starts quickly, even when cold, and doesn't need the choke more than about 30 seconds. But when on the road, especially from a stand still, if you hit the throttle with anything but the most gentle hand she bogs down (at first). Even rolling, if you nail it down low, she hesitates before taking off. Once she hits about 3,000 RPMS... hold on. She pulls like a freight train all the way to redline. The warmer the engine, the less pronounced the hesitation, but it never fully disappears.

FYI - when I say "bogs", she doesn't do a textbook bog, where the power just falls on its face... she kind of hesitates and misses a little, almost like the timing advance is lagging the throttle, but it eventually gets there. I'm not sure how a timing advance could be delayed but still work....

The bike was wrecked when I bought her, and she'd been sitting for the better part of a year. So I threw some Seafoam in the tank, hoping this will help. She had been stored properly for the most part, but sitting that long is never a good thing.

Any thoughts on what I should check?

Sounds like a rich condition but you could check your timing advance to make sure it is lubed and not sticking.

If the issue persists, even with a correctly functioning timing advancer, would suspect clogged carb pilot circuits.

Good Fortune!

Have you gone through the carbs (cleaning, plugged pilot jets, clean air filter etc...)...?

Electrical circuits (coils/ignition components (Points-condenser or EI)/connections/charging etc...) all to specifications...?

Voltage at the coils...?
Charging system voltage to specifications...?

Valve clearance/shim adjustments to specifications...?

Camshaft markings (tooth count) aligned to spec...?

Think that would be a good starting point for confirmations...

OMR

Here's a diagram showing how to spray carb cleaner to assure it's exiting into the carb throat.

This test assures that the tiny passageway into the pilot circuit is clear

On carbs fitted with plugs over end of pilot jets, the plugs are essential.





On later model BS34 carb that eliminated the plug at end of pilot jet (and I believe also eliminated the tiny passageway), may spray carb cleaner directly into the pilot jet to assure the spray exits into the carb bore.

The objective is to assure that fuel mixture may travel through the pilot circuit into the carb bore to be sucked into the combustion chamber.

Good Fortune!

Based on what you describe [gets better as the engine warms up] I'd say your pilot circuits need to be richened up. Drill out the fuel screw plugs and adjust your pilot fuel screws. If you need more than 3.5 turns out, go up on the pilot jet one size and start the screw adjustment process over. Out is richer, in is leaner.

Good stuff, guys... I will start at the bottom (easiest) and work my way up (hardest). When it is solved, I'll report back here.

OK... first things I did - I pulled the old K&N that the previous owner had put it. I am in idiot for not checking this, but... cleaned out great big gobs of greasy fur ball stuff from the bottom of the filter. Then I opened and lubed the timing advance per the Clymers manual.

Hesitation is gone. Completely and utterly GONE. MAN this baby is fast!!

Thanks for the suggestions guys!!