High Idle

Hello all. First time poster here but have been a regular visitor to the site. I picked up a 77 kz400 recently. Seemed to be running good when I first got it but lately I've had a couple issues. First off, when I first take off it'll start kind of chugging or sputtering out, however you describe it, kind of like it is running out of gas. I'll throttle down a little more and it goes away until I go to the next gear. 2nd...after going for about a 15-20 minute ride, I'll stop and its idling really high. When I first start it up its idling around 1000 rpm's but after riding for a little while it idles much higher when I put it into neutral.

Could these issues be related? I know I can adjust the idle but its fine when I first start it so I didn't want to mess with that. Hoping its a simple fix. Any input would be greatly appreciated. Thanks!

Carb holders. Do the thumb test on the diaphragms.
Steve

I did spray some carb cleaner around the carb holders while it was running to see if it affected the idle at all. No change in the idle. My first thought were the carb holders as there are some minor cracks but it doesn't appear the cracks are very deep.

Me being somewhat of a newbie here, I have to ask, what exactly is the thumb test on the diaphragms you suggested?

Thanks!

The large opening at the top of the mouth is a vent. Put your thumb over it while the slides are up with your finger and not if they fall slowly, quickly or the same. They should fall slowly.
Steve

You say the bike idles at 1000 rpm's when you first start it, but you do not mention if you are using the choke for a minute or two first and then it's coming down to rest at 1000 rpm's. What it sounds like to me is that your idle screw is set so you don't have to choke to start and you don't let it warm up much before hopping on the bike to ride it. Then once it is properly warmed up the idle jumps way up. I would back the idle screw back down and use the choke for a bit on initial start up.

Are your carbs push and pull? If they are make sure you fully close the throttle and at the same time adjust the cable at the carbs tight down this can stop high tick over and hanging revs when it's warmed up , hope this helps.

Bama704 wrote: You say the bike idles at 1000 rpm's when you first start it, but you do not mention if you are using the choke for a minute or two first and then it's coming down to rest at 1000 rpm's. What it sounds like to me is that your idle screw is set so you don't have to choke to start and you don't let it warm up much before hopping on the bike to ride it. Then once it is properly warmed up the idle jumps way up. I would back the idle screw back down and use the choke for a bit on initial start up.

This.