1980 kz 550 loosing power

hi, I have brought a 1980 kz 550 that has sat for around 20 years and I got it running but the problems that I am having are after I let it warm up I go take it for a 5 min ride and it starts to loose power, it revs very slowly under load but when I stop and rev it it revs just fine. That only happens when the bike is all warmed up, when its cold it has all the power. also when I rev the engine real fast at low idle the bike just dies, also most of the time the bike does not want to return to a even idle after revving it. what would cause these problems?

I have rebuilt the carbs with stock jet sizes,
new (used ignition coils) with new plugs, plug boots and new wires ( made big power difference)
bike is all stock except for a dyna s electronic ignition that the last owner installed
Compression test is around 150psi on all cylinders, no smoke, no strange knocking

Probably a vacuum leak at one (at least) of the carb holders (rubber boot between carb and cyl head).

Spray some ether ( or wait for later suggestions if not sure) at the boots where they meet the head while the motor is running. If the motor speeds up, then you found the leak.

Would also check valve clearances to determine whether they are in specs.

Good Fortune!

i did not find a vacuum leak, the bike idles fine on all 4 cylinders its just when its warm it looses power it feels like its only running on 3, when it cools down the power is back, the coils aren't hot, could this possibly be caused by float bowls being un even? i checked them today and did not find much of a difference between them, when i had the carbs upside down i could see one float a little higher than the others. would this problem be fuel or spark related.

the bike also has a little over 13000 miles and i dont hear any valves ticking, would my symptoms possibly be tight valves?

michalw wrote: i did not find a vacuum leak, the bike idles fine on all 4 cylinders its just when its warm it looses power it feels like its only running on 3, when it cools down the power is back, the coils aren't hot, could this possibly be caused by float bowls being un even? i checked them today and did not find much of a difference between them, when i had the carbs upside down i could see one float a little higher than the others. would this problem be fuel or spark related.

You cannot accurately measure carb bowl fuels levels by looking at the floats. The only way to tell what the fuel levels truly are is the "clear tube" method. See link below:

kzrider.com/forum/2-engine/580335-homead...at-level-tool#580344

after I let it warm up I go take it for a 5 min ride and it starts to loose power, it revs very slowly under load but when I stop and rev it it revs just fine. That only happens when the bike is all warmed up, when its cold it has all the power. also when I rev the engine real fast at low idle the bike just dies, also most of the time the bike does not want to return to a even idle after revving it. what would cause these problems?

Would also check valve clearances to determine whether they are in specs.

bike idles fine on all 4 cylinders its just when its warm it looses power it feels like its only running on 3, when it cools down the power is back,

the bike also has a little over 13000 miles and i dont hear any valves ticking, would my symptoms possibly be tight valves?

Yes.

Absence of audible ticking is inconclusive, and would actually be consistent with too tight valves.

Acceptable cold performance deteriorating when warmed is classic symptom of a too tight valve.

Perhaps valve clearances have never been checked.
Would suspect 13,000 miles is likely well beyond factory instructed routine maintenance.

Clearance is quick and easy to check.
Simply place thickness gauge between cam and bucket with cam lobe pointed away from the bucket.
Clearances might be within spec,

Good Fortune!