Rough running

I have a 80' kz750 that has never run right since I got it. I recently cleaned the carbs and put them back on. It helped the idle and full throttle, but normal acceleration causes it to sputter REAL BAD. Also it is very slow to throttle down after I release the grip. I tried blocking off the vacuum lines but no difference. Anybody got a suggestion? I'm desperate. This is my only means of transportation to my Doctors office and I need it running right.

Thank you

More information would be helpful. What model 1980 KZ750 (they made 2 and 4 cylinder KZ750s that year)? What, if any mods have been done to bike (stock air filter or pods, exhaust, etc.)? What other work has been done on bike (clear tube test, recent tune-up, etc.)? What do you mean by "tried to block off vacuum lines" -what vacuum lines? A picture or 2 of your carbs would also be helpful as you may have the plumbing hooked up incorrectly. Ed

Also, please describe how you cleaned the carbs. Did you take them off the bike and spray carb cleaner in them or did you completely dissassemble them and soak them overnight in carb cleaner?

Battery - charging electronics rectifier/regulator - ignition electronics all to specifications...?

Valve clearance & ignition timing to spec...?

Sparky conditions (fouled/carbon build up/oily etc...)...?

Coils & Plug wires to spec...?

Check for a vacuum leak.
When at idle Spray the intake boots with carb cleaner where they meet with the carbs and also where the boots meet with engine. If the idle goes up u have an intake leak. Make sure the carb holders are screwed on tight enough to make an air proof seal but not too tight to pinch the boots.
Intake leaks are very common after reinstalling carbs.
If there is no vacuum leak double check that the slides are moving up when u pull the throttle.
If the rubber diaphragms are not sealed correctly they will not lift and the engine will not receive fuel when the throttle is pulled causing the engine to die.
The hanging idle u describe is a symptom of a lean condition. And what u describe sounds like an intake leak.
Whether it is or isn't caused by an intake leak, what u describe definitely sounds like the engine is not receiving enough fuel.
If the vacuum line u are referring to is the one coming out of the carbs, u need to remember that if your petcock is vacuum operated, and in the on position, plugging this line will only keep your carbs from filling with fuel. This hose needs to be hooked to the smaller petcock nipple in order for gas to flow. If U do uplug it make sure the petcock is in the prime position.
Make sure the idle screws are turned out per the manufacturers recommendation.
Good luck and keep us updated.
Worse comes to worse recheck your work.

i would check the air filter mine had a k&n filter that made it real touchy from right until 1/8 throttle. the regular air filter makes a big difference with getting the carburant into the cylinders. don't listen to Jamie m. because you will get frustrated as nobody likes a know it all. also make sure the clean air system is in order along with the overflow tubes on the bottom of the carburetor must remain unplugged.

If this issue is related to the fuel air mixture, u can get an idea by looking at the spark plugs.
If they are sooty and black ur bike is running too much fuel.
If very white then too lean. U can find photos online of the correct color your plugs should be.
The issue u r having could be related to fuel mixture or ignition.
Do all of the exhaust pipes feel equally hot after a minute of running? (lick your finger and tap them lightly to not burn yourself)
If one is colder that is the cylinder with the problem.
Did u sync your carbs?
Maybe isolate your cylinders to see if the problem seems to stay in one, cylinder or all, or only when running together.
B4 focusing on air or fuel make sure it's not electrical.
To check spark , do this,
pull the plugs out and then put them back in the plug wire. Let the spark plug lay against the side of the engine. Hit the starter button. watch to make sure you have a strong blue, regular spark.


But b4 diving into the carbs a second time, check to make sure u have a strong spark.
The last guy is right about checking your air filter. Make sure it is clean. Any air would cause acceleration issues.
I'm not a know it all but I do work in a motorcycle repair shop. And im certified. So I know a little.

Mine used to pull that crap.

Valve job champed her right up!

Get manual, get shim kit, get feeler gauges, get tequila, get decent $5 cigar, get socket set, get to wrenching.

Learned it from YOUTUBE!@

I will have to agree with the checking the spark plugs but be careful the threads are really easy to pull out with the spark plug if it runs too hot. i would take some marvel mystery oil and rub it on the head pipes so you can check the color of the pipes after it runs to see what one runs the hottest ie color of the oil on the pipe.
I wouldn't pull the top of the carb off until you are ready to replace the slide vacuum rubbers. what mine did was idle up and down when i turned the idle screw too high, i am pretty sure the o-rings in the mixture screws were missing and one of the float clips was missing along with an incorrect float setting. there is a way to check the float level with the bike level on the stand, something to do with the overflow tubes.
Furthermore the timing is non adjustable and the petcock is vacuum operated.
if you try to synchronize your carbs yourself you are up the creek without the proper tools.

80 kz750 h1-4 20,500 miles

get it going and prepare for 60 mile per hour winds.