New KZ650 Project for the Michigan Winter!

  Hello all!
I'm somewhat new to this forum, but it has already helped me quite a bit in the last few weeks. But as I'm getting deeper in my resto-mod project, I thought it was time for me to join.
I have been riding all kind of motorcycles over the last 3 decades, on several continents. Of course, I had my share of technical issues leaving me stranded on the roadside. But so far, I never had to go too much into engine mechanics.
More recently, I bought a half-dead 81 Honda CX500. The bike was falling apart: no working light, no brake, misaligned fork, leaks everywhere. But the engine was running! The previous owner had only rebuild the carbs. And so I thought i could do something with it. And I did, the CX is now kind of scrambler. It will be finished this week when my friend will have repainted the tank. 
And so of course, now that I have the "bug", I needed to pick-up another project for the cold Michigan winter! I looked for several month and came across a 80 KZ650 LTD. The bike is in pretty good shape, 95% stock. The previous owner only changed the mufflers, the rear shocks and repainted the tank and fender on his own. (my friend who is a pro painter at Ford almost vomited when he saw that paint job ). The bike was still ridden in 2024 but hasn't been touch since then, without any winterization. So, of course, the carbs were all gunked-up and the slides were stuck.

I took the Mikuni VM24SS carbs out to give them a partial clean. I mean, I took each carb one by one, opened the top, spray carb cleaner until i could take the slide assembly out. I then put the parts in my ultrasonic cleaner and blew-dry everything. All slides moved super smoothly. I then put the carbs back in place with new air boots, a new air filter and a fresh battery. I also emptied the tank and put in fresh non-ethanol gas mixed with Sea Foam. And after realizing that I need to squeeze the clutch (thanks to this forum), the engine started right up! Yay!

Now where I will need help is for what comes next. The engine only idle with the choke. The RPM's are not stable, then go between 2,000 and 6,000 on their own. And the minute I touch the throttle, the engine bogs down. Reading a good few posts here, it looks like a could test many things, but since the bike was running good (I mean daily rider) last year, and I did clean the carbs thoroughly, I'm suspecting that my first step should be to take the carbs out and truly disassemble and clean them.

What do you guys think?

Welcome to KZRider
I fixed your picture to be full size .
Next time click the insert all tab to complete the install
Where in Michigan are you.
Some of us get together and work on bikes at my place in Livingston CTY
by Brighton  (Zukey Lake )
Nice project
Dave

Welcome from the UK

Thanks for the welcome! ... and fixing my post.
Funny you are in Michigan too because I'm only 15 miles away, somewhere between Dexter and Chelsea. Small world!

Welcome from Canada.

Seems an air leak is always mentioned when idle seems to be errattic. 
You can try spraying something WD40 (?) around the carb manifolds while she's running.
If there's a change in RPMs, there's a leak.
How are the rubber caps on the carbs/holders, if applicable.
Later models didn't have the rubber caps.

Thanks rstnick!
I will test for leaks tomorrow morning. If i find some leaks, i'll try to address them before moving on. But if i don't, would my next step be to take out the carbs for a deep clean? Last time I chickened out and didn't open the float bowl.
And yes, you're right, I don't any caps on the carbs holders.Only carbs 1 and 4 have a sort of vent tube.

Welcome from Georgia! 
I see you cleaned the carbs, but did you pull out the pilot jets and make sure they were clear? Running only on choke usually points to dirty pilot jets. 

Hi! I've squirted some WD40 on manifold carb holders this morning and it's not conclusive unfortunately. 
The bike could only start with starting fluid. Then the rpm still fluctuate a bit. Of course there is a drastic change when i touch the choke. 1mm one way, she revs up to 6,000 rpm, 1mm the other way, she dies.

Seems an air leak is always mentioned when idle seems to be erratic. 
You can try spraying something WD40 (?) around the carb manifolds while she's running.
If there's a change in RPMs, there's a leak.

So now, I'm really tempted to take the carbs out. What do you guys think?

Thanks ThatGPzGuy,

No I was afraid of messing the jets so I didn't open the float bowls. I blew compressed air everywhere. But now that it only runs on the choke, I'm thinking I need to go back and take it all apart. After all, it can't be worse than now.

Rideallyear wrote:

Hi! I've squirted some WD40 on manifold carb holders this morning and it's not conclusive unfortunately. 
The bike could only start with starting fluid. Then the rpm still fluctuate a bit. Of course there is a drastic change when i touch the choke. 1mm one way, she revs up to 6,000 rpm, 1mm the other way, she dies.

This method is a bit "hit and miss" unfortunately but the best you can do if you don't have access to an exhaust gas analyser (air leaks show as a high Hc reading) how old are the carb to head rubbers ? if original or unknown replacement (ideally with OEM) is recommended. They harden with age and don't seal around the carb throat, also they can become porous due to micro cracking

The previous owner had the carbs cleaned by WiredGeorge about 10 years ago. It seems that the head rubbers were changed at the same time (especially compared to the rubber ducts on the air box). But i'm really not sure.
So if I have taking the carbs out again, I might change them and be sure.

When you remove the carbs and go through them, check the jets and make sure they are not generic "carb kit" jets. If they are, replace them with the correct ones. If they have not been replaced, clean them thoroughly and make note of the sizes for future reference.