84' KZ750 L4 - Extremely High Idle!

Hey all, I have a 1984 KZ750 L4, I recently have taken off the throttle cable and lubed it, also replaced the starter switch/throttle casing. I replaced the plugs and wires as well. I was having serious trouble starting the bike since I purchased it about 2 years ago... So I finally traced that problem to the starter, which was grounding out on itself, which i fixed. So now with that fixed the bike starts up nice and quick, but will now Rev up to 4-6Rpm so I shut it off immediately and have been troubleshooting. I started by checking the idle pin, which was fine, the response both at the throttle grip and at the carbs is a nice quick snap back, I took the carbs off and gave em a good bath and air clean. Oh and I replaced the air filter in the air box, the one before had nearly disintegrated could it be possible some of that is caught somewhere within the engine?. Ok so after the bath I put the carbs back on and checked the service fuel level which was fine, oh and I found the specs for the pilot screws which is 2-1/8th turns back so they should be right? So with the carbs back on and connected I started the bike, which started nicely, and was Idling at a more reasonable level but still high (around 1500-2000) but then out of the blue after a couple mins it kicked back up to around a 4000rpm, choke all the way in and idle pin backed out, I did fiddle with both of them, but it didn't make a difference. One thing I did notice, is on the choke shaft the third rubber boot or plunger was torn, would that be causing the high rmp's? or is this still possibly a starter problem? or I could re check the throttle cable to see if it's set right? I'm pretty sure it is... ANY SUGGESTIONS WOULD BE AWESOME!!!

I am gonna suggest checking your fuel level(tank) and that your petcock is working properly. For whatever reason, when my bike runs low on fuel, the idle shoots up.

Ok I will for sure, thanks!

she is on lower level of fuel, but I did have a full tank before when this was happening as well so I'm not sure that's the issue but def. worth a try. From what I can tell the petcock is working fine, the vacuum line to the #2 carb seems okay as well, and with the tank off fuel flows from Prime only. I'm thinking it may be a jetting or syncing issue with the carbs? which I don't know enough about...

In the case where the throttle cable was removed it's important to make sure you have some free play in the cable with the throttle setting on the stop, and make sure the stop is set low enough too. Assuming thats the case, it could be a vacuum leak. Not sure about that choke boot but I'd fix that straight away. Petcocks don't cause issues like noted unless it's causing a vacuum leak itself. Some people suggest using carb spray or what have you on the carbs to look for a change in idle, thus confirming a vacuum leak, but that's an unreliable method in my experience. However, if you do experience a change when doing that, you can be assured there is a profound leak.

Got ya! hopefully it's not raining tomorrow, and I can take a look at the throttle cable play, If not a vacuum leak could definitely be possible, you mentioned the carb spray method being unreliable Is there another option other then finding an actual vacuum tester that you would recommend?

I'm hoping it's just something to do with throttle cable as mentioned, and thinking back, it was the first thing that I mucked with, before this issue started.

I appreciate the help thanks very much!

Solved the idle issue!!!!! It was a combo of a vac leak, and the idle adjusting pin, and a bit of fine tuning with the throttle stop as well. and with clean carbs and new plugs, wires, air filter She is idling at 1100! and snapping back better then ever!

I did take it out for a test run around the block, and it was loosing idle really quickly and stalling out, took it home consulted the specs in my manual and it turns out I was missing a spring in the idle pin to keep it set. so found a spring popped it in and went out for another run...

I must have messed with the clutch when I took the shift pedal off and the casing to get access to the starter because it's only shifting down to 1st, and up to neutral.

raining again today...