Question about K 75S throttle response

[earlguy]

I'm noticing my new to me  1990 K75s  has a jerky throttle response , it's not hesitent but it's not smooth either. I have to turn the throttle grip very slowly to get a smooth response. Should a smooth acceleration or jump when the contyrol is turn just a bit? When backing off the throttle I feel the same jumpy response. I am wondering if this is normal or prehaps a symptom  of  throttle body sync problems.

The bike Idles  smoothly when cold but needs a bit of choke for about a minute or so  at temperatures of around 80° .

 I really appreciate the site. I am loving this beast!

[Laitch]

Throttle response should be steady from idle to full. Are you referring to the action of the throttle or the response of the engine? Is the engine surging or stuttering? My first inclination is toward throttle linkage needing lubrication but further description might be beneficial.

Have you looked into the fuel tank for debris? Have you looked at the throttle linkage in the right switch/brake cylinder housing to check on lubrication there? What systems have you reviewed—spark plugs, air filter, fuel filter, valve clearances? How much do you know about the previous maintenance of this used moto? How many miles are on the odometer?

Answers to these questions help respondents understand what you're likely up against.

[The Mighty Gryphon]

With the bike on the centerstand and the transmission in 1st gear how much rotational play is in the rear wheel?  There shouldn't be more than a half inch.

What kind of shape are the drive shaft splines in?  Can you post clear photos of them, especially at the final drive.

These machines do have a bit of lag due to the barn door in the MAF air flow sensor.  When the throttle is opened quickly it take a few milliseconds for the air to move the door and thus increase the amount of fuel mix into the engine.  With the later Motronic units on the 4 valve engines the barn door is eliminated in favor of a throttle position sensor that sends an instantaneous signal to the ECU.  This eliminates the momentary leaning of the fuel mix that happens with the earlier Jetronic ECU's.

[earlguy]

Thanks guys!

I keep the bike in N Woodstock,NH. We will be headed there later next week so I can take a closer look then. 

By jumpy I mean the engine seems to accelerate about 20 -30% to quickly too quickly which makes slow speed maneuvering more challenging. I would like to have a more graduale and controllable throttle response.

Just received the Clymer manual, it looks great!

 Appreciate the suggestions.

[earlguy]

Just wanted to say thanks for the suggestions. I found a vacuum leak and and ran a throttle body sync, the bike is much smoother now.