1982 KZ550 LTD low top speed?

Hey guys, I have a 1982 KZ550 LTD with about 22k on it. It's been a fixer-upper, had trouble idling and warming up (meaning, it wouldn't. Had to use the choke just to sit at stoplights after even an hour of highway riding), and could not accelerate over about 45 without going down hill. Finally, about a year ago my dad (who owned a KZ900/1000 back when he was in college and worked on it frequently) took the carbs from me and did some adjusting and such. Now it idles perfectly at about 1k in cold weather and maybe 1.5k in warm, it warms up perfectly within a matter of about 5-10 minutes of idling depending on temperature and never needs choke again after that, and it has plenty of pickup and speed for around town. I can easily cruise at 55-60 without an issue. But the other night I had to drive up to a friend's place and, since it was about 3am coming back and the interstate was empty, I decided to see how it did at 70+ mph. Thing is, I topped out at maybe 60-65. I could boost it to 70 if I went downhill, but not otherwise. Like I said, it has plenty of power around town, but not on the interstate. I read that the top speed is supposed to be somewhere closer to 110 mph.

I'm considering selling/trading the bike off, since I would like to try out either some offroading or sport, but if funds don't work out I'd like to be able to use this to its full potential. Right now I don't trust taking the interstate even for a short jaunt. Do you guys have any ideas on what I could do (that is low to no cost) to get it up to speed, so to speak?

Does the bike have the stock airbox and air filter? Ed

Yup, the bike is completely stock, unless the PO did something that I can't see.

Anyone have an idea? I'd like to get the bike to where I could take a trip I have coming up on the bike instead of my car.

It sounds like the bike needs a full tune-up and needs the carbs cleaned. Dirty carbs will definitely kill the top end. When you say it "topped out at 60-65" what happens when you hit that speed? Does the engine keep revving up but the bike not accelerate - that would be the clutch slipping; or won't the engine rev any higher when traveling at 60-65? Ed

Check the timing advancer, and then after that the main jets on the carbs.

If the symptom is that it stumbles at WOT, then it can be the coils are weak, or plug gaps are too wide or igniter is failing. But it sounds like you're saying it just doesn't go fast, but is still sounds to be firing.

If that's not it, time to start looking at a compression test and valve clearance.

When I reach that top speed, it's as though the engine just can't go any faster. Like going up a hill in a high gear -- you can put the throttle all the way back and hear the engine under load, but it's just not going any faster. But the RPM's aren't going up or anything that would indicate clutch slippage. I also don't notice any stumbling at WOT or missing cylinders. Plugs were replaced and gapped a year ago, along with plug wires. I checked and double checked (and quadruple checked) the timing advancer and everything related to timing when I had the cams out well over a year ago, so I believe everything there is fine. I don't remember checking compression (other than poor-man's test, which all cylinders passed equally) or valve clearance.

The carbs were cleaned well when they were adjusted last year. I honestly don't remember trying to take it up to 70 then, but I also don't remember having any trouble. Do you guys know of a good method to clean the carbs without taking them off the bike? (something I could do with access to only an apartment parking lot)

By checking the main jets, what do I need to look for? I'm still learning, and this is the only carb fed system I've ever worked on (always been fuel injected cars).

Since you have limited facilities to work on the bike, I would recommend doing a compression test. It will cost a little money, but it's an investment, and the test does not require anything else other than a sparkplug wrench, which should be in the toolkit if you still have it.

Cleaning carbs and adjusting valves (read the warning in my signature), are a lot more involved, and you will probably want to wait til you have a better place to do those items.

Also, you should be doing everything per the manual. I have several you can download in my signature.