KZ550 overrev.. loss of power now.. please help

[dxiw]

To summarize what happened:

I was riding my 82 kz550 down to work (as I do everyday) with no problems. I was quickly accelerating from a stop and at around 7000 rpm in first gear, I made my usual shift into second. I somehow miss the shift and end up in neutral (I know what a retarded mistake..) and the engine revs for a couple seconds to the highest the tach will read (12000+ rpms on a 9500 redline) in which I immediately let off the gas.

When I started to ride again the bike seemed like it lost all of its power. I rode it two miles home in this condition. It seems like it has no torque. It revs up very slowly (even with a ton of throttle) and then once it hits like 4000-5000 rpm then it kicks in power in a choppy way. In 2nd or 3rd gear, it doesn't have enough power to accelerate much at all unless I nearly give it full throttle. It literally takes me 30 seconds to get up to like 30 mph. I notice in first gear if I give it a lot of gas, it will rev up very slowly from idle to 5000 or so, and then all of a sudden a ton of power kicks in and it throws me in a wheelie.

Any advice?

The two things I was thinking were:
1. The carburetor's throttle slide is stuck, so it can't create vaccuum at low rpms.

2. The valves in the engine got ****ed and so only one or two cylinders are giving power at low rpms. But then as it revs up, at high rpm, the valves start to function correctly and all of the cylinders kick in.

I would def appreciate any help.. thanks

[shoodaddy]

My immediate guess is that you floated some valves and probably hit the pistons. I don't know if your engine would do this, some will and some won't.
You probably need to do a compression check as your first test. Best to use a gauge, but you could pull the plugs and crank the motor for a second with a finger covering the sparkplug hole, compression should easily blow your finger off the opening. My guess is you no longer have compression on at least two of the cylinders, Shoo

[dxiw]

I was thinking that could be the problem, but the fact that it revs up and runs high power at high rpms means that those cylinders are getting compression imo. I agree with the valves. I completely removed the carbs and airbox and I'm going to pull the engine out of the bike on Sunday so I can take the head off and see whats going on. Do you think there's any chance that the carbs could be at fault (should I rebuild the carbs tonight)?

[shoodaddy]

If the bike ran fine up until you overrevved it, why would the carbs suddenly be at fault ??? Like I said, easiest thing to do is do the thumb test for compression. If you don't blow your thumb off the hole you are narrowing down your possibilities. Let me know how you make out, Shoo

[elr658]

+1 shoo. You need a compression gauge to tell you you're beat.
A leakdown test will say how much and where you're beat.

[rocketkiller84]

Does the bike smoke or any strong smells come out the exhaust ?

[dxiw]

UPDATE:

So, I took the carbs off and cleaned them (they needed to be cleaned anyways)...

Then I had this random idea. Perhaps, my problem was ignition because it was happening under the most load (resistance at low rpm). So I installed 4 new spark plugs and reinstalled the newly cleaned carbs.

The bike started up well and I took it for a spin and it seemed like my problem was fixed.. a lot of the power I originally had was back (if not all - it was hard to tell). I then realized thought that the engine sounded a bit funny so I tested the ignition coils and realized that only 3 of the 4 cylinders were actually sparking. It seems my wires had gone bad because that fourth one was shorting out before it reached the cylinder. I'm going to pick up new wires tomorrow (and pods so I can get rid off my filthy airbox) and give an update.

But the good news is that the bike runs!!

[elr658]

Run the airbox. You'll thank me later.

[dxiw]

So I put on the new ignition wires today.. and took it for a run - it was fast and running great..

But, when I opened the throttle all the way it revved up and began to choke itself out, as soon as I let off the entire old problem was back!!!!!

I let the bike cool down for several hours and tried to run it again and bike once again has no power. It feels as if the mixture is incorrect because it backfires and chokes itself out no matter what.

I think maybe something is getting stuck or messed up in the carburator when I open the throttle significantly and screws up the mixture until the carb is physically emptied of gas and rebuilt... any ideas what else it could be??

[Norseman10]

dxiw,
Excuse my ignorance, but why would you run her up to 7k rpm in first? You've past the point of diminishing return way before 7k - your KZ550 ain't an R6. Ditto and +1+1 on shoodaddy and elr658, you might want to take their advice to heart. They actually know what they're talking about (having saved my bacon a few times ).

Check compression, my friend... Sorry to hear about your troubles, sounds like it's your daily rider and you're out a ride. That stinks.

[dxiw]

I will check compression tonight..

Just one quick question: Don't you guys think there's a carb problem somewhere, since if I drain the float bowls and drive it gently it works like a clock, but after being full throttle, it won't work until I drain the float bowls??

[antiq]

I'm not a racer and the thrill of rebuilding engines is long past. I can honestly say I never get too close to the redline on any of my vehicles.
Why the fixation on the carbs? If the valving got messed up you can be pulling more fuel from them at all stages than they are set up to provide.
Norsemans advice is good. You've been given good advice follow it.

[dxiw]

Ok so I bought a compression gauge and measured compression:

Cylinder 1: 121 psi
Cylinder 2: 120 psi
Cylinder 3: 119 psi
Cylinder 4: 121 psi

So, compression looks good, at least good enough.

And the good news: I figured out the problem, or at least part of it. I noticed that when the problem occurs only 2 of 4 cylinders are firing (both are on one of the two coils). I suspected the other coil was leaking at the cap, so I put some dielectric stuff in the cap and screwed the ignition wires on tight and voila! all 4 cylinders were firing!!! So, now the bike is drive-able and seems to have restored it's power, but I'm not making much additional power at 7k+ rpm. I assume that this is normal from the previous comments.

I will go for an extended ride and let you guys know if I notice any abnormalities.