Topic: CB750K3 throttle hesitation

[junior]

Now that I got 350 miles in it, it developed a hesitation when cruising in all gears, in the middle of throttle roll off and roll on. Everything is stock, intake and exhaust, jetting, needle setting. I did the Honda man mod to the emulsion tubes too. Could this be gas related? I did a fill up about 25 miles before noticing the hesitation that it did not have on the first 300. Thanks, Gary

[HondaMan]

What RPM are you typically running when you roll it on? If below about 2800 RPM, it may stumble with a big handful of throttle.
Also, check your sparkplug color: see if they are getting black. That leaks away some of the spark, which will make for weak ignition, and similar stumbles.

The idle-mix screws: what setting are you using for them?

[junior]

Thanks for the response. I'm slowly rolling on at about 3k. My Idle air screws are set at 1. Plugs are medium brown. I didn't notice this hesitation until just lately. Was wondering if its gas related. Gary

[HondaMan]

It's possible: the gas here in Colorado is nasty and has flat spots and poor hot-run performance. This is new here, due to butane having recently being blended into the fuels (long story, all political, though). To smooth out the fuel, I use about 2 ounces of oil (doesn't matter much what kind) in the gas tank: this helps to stabilize the burn rate and removes the stumbles for me. But, I live at about 6000 feet altitude: your results may vary? It doesn't make the pipes smoke, but sure helps with cold starts and pulling away from a stop in hot, heavy traffic.

[Dunk]

Interested, I have a K5 daily driver with an annoying stumble somewhere between 2500-3500 RPM light load cruise when slightly opening throttle. Hasn't always done this, off and on between carb rebuilds  and miles over the year but is back to doing it. Granted weather has been around 100* for a bit that it seems more prominent, maybe related. Changed the oil today, it's overdue. I'll adjust valves, tension cam chain, and sync carbs tomorrow... also likely overdue.

Mine has a Dyna S and iridium plugs, for reference. Generally seems to make for easier cold start and smoother cold running than points and copper plugs. I should probably check timing, haven't done that probably since installing the Dyna.

[HondaMan]

Interested, I have a K5 daily driver with an annoying stumble somewhere between 2500-3500 RPM light load cruise when slightly opening throttle. Hasn't always done this, off and on between carb rebuilds  and miles over the year but is back to doing it. Granted weather has been around 100* for a bit that it seems more prominent, maybe related. Changed the oil today, it's overdue. I'll adjust valves, tension cam chain, and sync carbs tomorrow... also likely overdue.

Mine has a Dyna S and iridium plugs, for reference. Generally seems to make for easier cold start and smoother cold running than points and copper plugs. I should probably check timing, haven't done that probably since installing the Dyna.

Dunk: for yours, check that the spark advancer isn't getting to full advance too soon. Most of them today are: the years of heat-treatment softened the springs, letting them advance sooner than 2500 RPM. With modern gas, a too-soon-advanced spark often makes the bikes stumble.

On my own 750K2, the spark doesn't reach full advance until a little over 3000 RPM. That's what it took to smooth mine out (and lots of others that I have rebuilt) in hot summer traffic, heating up the fuel in the tank, etc..