1981 kz650 h1 needs some help

Hi all I received a all stock csr 650 from my father in law and it came in really good condition. (Here comes the but) but it doesn't run like it should. I have been told mechanics have been in the carbs. And so far I have seen that all the main jet needles have been moved and are visibly different from one carb to another and not by small amounts. Here's where I have the bike it can run and idle just fine fires up like a regular bike when cold choke it and when it's warm shut it off and it idles. I can get the bike moving it responds well, below 3800-4000 rpms then it falls on it's face and just isn't what it should be. The plugs are black and are the recommended plugs for the bike they have a blue spark after I let off the starter I got a new battery not too sure of the charge but it came out of my vn750 and it cranks. Air filter is clean. I am a decent mechanic I just don't have all tools. And I need some guidance with these things. Does anyone have any ideas what could cause this? Just falls flat at more then 1/4 throttle.
Update: got the mixture leaned out and it is doing the same thing.

You didn't mention the ignition advancer unit. Make sure it's not frozen and moves to the full-advance position when revving. You need a timing light to check the actual timing spec, but if it moves freely, it's probably good enough to run to red-line.

Thank you for the response I was digging around in there it seems like the advancer is free moving and opens fully but is a little rusty and the pickup for the signal is looking close to brand new and I am wondering if something is going wrong there

Pics of the plugs and bike? When was the last time the valves were adjusted?
Steve

I would check the ignition Timing/advancing movement with a Strobo light for correct timing, Rust particles on the pic-up and advancer can mess up the correct ignition timing.

I will get back to you all when I can next work on the bike it's just to hot being over 100°. I do not know when the valves were last done up. Will do for checking the timing and I don't have any pictures of the plugs currently I will post them as soon as I can. Thank you for the support. So far these are the only pictures I have of the bike. My other one is a xl250s from 1979 with just over 2000 miles on it.

"And so far I have seen that all the main jet needles have been moved and are visibly different from one carb to another and not by small amounts."

Can you add a little bit to this description? What do you mean when you say the jet needles have been moved? Were they raised? What is the number on the needle and what notch are they sitting in now?

The air intake looks to be stock. The carbs appear to need a good cleaning, at least on the outside. The exhaust is interesting...do you know how #2 pipe got rusted so badly? I am wondering if someone fiddled with the carbs when the OEM exhaust was replaced?

The needles in these carbs are different from regular needles usually notches are what you would expect but in this bike they use a screw that is connected to the throttle bar and the screw controls how much fuel you get instead of notches and the outsides are rough I don't wanna rinse it untill I get done tearing the bike apart and putting back together the insides are clean and clear. The intake is stock and I believe too that the exhaust is stock. I think #2 and #3 are both rusty because the bike was used as main transportation and driven in the rain often.

The stock jet needles on the 81 KZ650-CSR don't have notches (USA models).
If the jet needles are rough, someone may have soaked them in lemon juice or something.
I'm assuming you have the stock VM24 carburetors w accelerator pump.

1981 KZ650 Carburetor specification table. notice the USA jet needles don't have a groove number.

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Big kountry wrote: The needles in these carbs are different from regular needles usually notches are what you would expect but in this bike they use a screw that is connected to the throttle bar and the screw controls how much fuel you get instead of notches and the outsides are rough I don't wanna rinse it untill I get done tearing the bike apart and putting back together the insides are clean and clear. The intake is stock and I believe too that the exhaust is stock. I think #2 and #3 are both rusty because the bike was used as main transportation and driven in the rain often.

WTF?

I think he means you can't adjust the jet needle height by changing the clip location to another groove, since there are no grooves, so he can only adjust the needles by turning the slotted adjusting screw. By throttle bar I guess he means the throttle arm or throttle lever assy.


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I think they can be shimmed, but it sounds like flow control is via a different mechanism than anything I'm used to seeing.