KZ550 performance question

Hey everyone.
I built my 81 Kz550 LTD a couple years ago. It has 9500 miles.I didn't buy it in running condition so I have no idea how it is supposed to perform. The 550 transmission is a 6 speed with 6th gear as an overdrive. The bike is fairly quick to accelerate but doesn't want to pull much over 65-70 mph. Is this just the way the engine is designed or is there something I can do to get the extra performance back?

As with every new(to you anyway) vehical, Do a full tune up. Buy a factory/Haynes or Clymers servise manual. Change fluids and do a full lubeing. Valve clearance. Carb clean and adjustment and sync. New filters are not out of order.
Your bike should do the ton(100mph) and more. Acceleration should be 0 to OMG! in the half blink of an eye. Enjoy.

The KZ550 will easily exceed 100 mph when it's running right, so I'm betting you have dirty carbs. Many years ago I screwed up and let my KZ650 sit for about 16 months without being run and with fuel in the carbs. When I finally started it up and rode it I couldn't get it to go above 50+/- mph. I thoroughly cleaned the carbs and performance immediately returned to normal with a top end right around 120 mph. Ed

azman857 wrote: As with every new(to you anyway) vehical, Do a full tune up. Buy a factory/Haynes or Clymers servise manual. Change fluids and do a full lubeing. Valve clearance. Carb clean and adjustment and sync. New filters are not out of order.
Your bike should do the ton(100mph) and more. Acceleration should be 0 to OMG! in the half blink of an eye. Enjoy.

...Good sound advice!

...You can't imagine what a good clean set of carburetors and properly adjusted valves will do for your bike's performance. Not to mention, the longevity of your ride.

The bike is fairly quick to accelerate but doesn't want to pull much over 65-70 mph. Is this just the way the engine is designed

No, seems it needs some attention. I've had 120 mph out of my GPz550, even a tired one should do the ton.

The 6 speed box is close ratio, not overdrive. Stick with it, they are great fun.

Hmmm... a few years ago, I had what I thought was a toy!! A late 70's KZ400LTD.... (400cc) and that silly thing would easily hit 80mph on the open road out here on the plains of Colorado!

The bike has all new hoses and boots so I have ruled out a vacuum leak. I installed new spark plugs about 500 miles ago. It runs on all four cylinders. The carbs were completely gone through at the beginning of the season but I never synced them. One side of the engine seems to heat up quicker than the other so I'm assuming the sync is probably at fault.

Normally carb synchronization doesn't have much affect at wide open throttle since tiny variances in slide height are a very low percent of the total open carb throat diameter. Carb sync issues generally have a much greater impact on the engine idling or at other very low throttle openings.

Is it possible that the fuel flow from tank to carbs is being reduced due to a dirty petcock screen or inline filter? Ed

Like Ed said, sync is not the issue. Can you post a video of the engine while revving? That might help us determine if you are running on all four. I've had more than one instance of helping someone tune a bike, but when they bring it to me, it turns out it was only running on two cylinders. Sometimes it just needs a new coil, and all is better. And if it hits a brick wall effect, then definitely look into fuel flow as Ed suggests. Also, check that the ignition is reaching full advance on both coils, this will also help to determine that all four are at least getting spark (connect the timing light to each plug wire in turn).

All four headers are extremely hot to touch so I'm assuming it's running on all 4. I took a video anyways so you could all hear it. I installed a plastic fuel filter from advance auto a couple years ago. Ill replace it with a new one just to be sure

...Is that left pipe all blue? Only got a quick peek from the video. Fairly unusual with a stock air box and stock pipes. That makes me think fuel, a lean mixture. Can you take a shot of all four pipes? Are you sure your float levels are OK. Sounds like your engine might be starving for fuel. That would explain poor top end and also the blue pipes. Which will also damage valves over time if you continue to ride with that condition.

Is there an air filter inside the airbox or did someone remove it? Ed