kz 550 power loss

I have a kz 550 and after the engine warms up it looses power. It just revs real slow under load but revs fine in neutral. when the bike is cold it runs good. I have rebuilt the carbs with stock jetting and replaced the coils with used ones from a 1981 kz 550. also has dyna s ignition. Any ideas what could cause this? Valves possibly? the bike has 13000 miles.

michalw wrote: I have a kz 550 and after the engine warms up it looses power. It just revs real slow under load but revs fine in neutral. when the bike is cold it runs good. I have rebuilt the carbs with stock jetting and replaced the coils with used ones from a 1981 kz 550. also has dyna s ignition. Any ideas what could cause this? Valves possibly? the bike has 13000 miles.

Would suspect too tight valve clearances.
Minimal clearance allows sealing when cold, but disappears as the engine warms.

If valve clearances found within specs, would remove and examine the spark plugs to diagnose a possible over-rich fuel mixture.
Could result from such things as dirty filters, too high fuel level, etc.

Good Fortune!

+1 on the valves. Don't run it much until you've checked them and re shimmed. You could burn a valve and seat. Also, spray some water on the pipes while it's running and make sure that you don't have an ignition coil that craps out when it gets warm. To the un trained ear, An engine running on two cylinders might sound O.K. and it would have no power. What you are looking for is the water boiling off of the hot pipes. If you spray water on them and it doesn't quickly steam off, That cylinder isn't running well. It would either be the #1 and 4 or the number#2 and 3 together. Any single pipe that is cooler than the rest would show a carburetor issue or maybe your tight valve on THAT cylinder.

If you don't have a factory manual, grab them from my signature.

Also read the valve train warning before you start checking the valves.

I gave the bike to my mechanic to do the valves since he thought it was the valves causing the problem, but im also wondering if it can be spark related. The power loss is kind of sudden but it gets spark to all 4 plugs. could the dyna s ignition be causing this problem? coils? igniter?

An ignition coil that is failing will often fail when it heats up..and then work again once it cools. The igniter would just fail and the Dyna is probably O.K. unless you have a pinched wire.

ZERO wrote: An ignition coil that is failing will often fail when it heats up..and then work again once it cools. The igniter would just fail and the Dyna is probably O.K. unless you have a pinched wire.

A simple way to check the coils is to ride the bike at high speed if possible to warm it up, then stop & feel them to see if they are getting hot to the touch - press hard w your fingers - don't get burned by the valve cover. They should be warm, not hot. My bike was running odd at speed - the coils were getting hot, hot, so I replaced them w green Dynas from Z1Enterprises.com.

Something else. A bad battery can cause the bike to run poorly.

You will want to make sure your mechanic knows about the valve train issue before he tries to complete the job. Most mechanics are unaware of this issue on KZ's. Older bikes, and new bikes don't have this issue.

so i got the valves adjusted and carbs synced and it still had the same power loss issue so i swapped the coils with ones from my dads goldwing which had the same omh reading and still did it. so then i took off the cover for the dyna s electronic ignition and took it out for a ride and had no more power loss issues, could the dyna s be causing the power loss after it gets warm?

anyone????

Check to make sure the Dyna wires aren't touching the cover when it is in place. Maybe dust the inside of the cover with something, install it, go for a ride until the problem occurs, then inspect the inside of the cover for telltale marks on the dusting. Ed

michalw wrote: so i got the valves adjusted and carbs synced and it still had the same power loss issue so i swapped the coils with ones from my dads goldwing which had the same omh reading and still did it. so then i took off the cover for the dyna s electronic ignition and took it out for a ride and had no more power loss issues, could the dyna s be causing the power loss after it gets warm?

Yes, for sure. That is exactly what flaky electronic devices do. But as pointed out, make sure the cover isn't touching anything.