Severe power loss with extended highway riding

Hey all, bike is a 1984 Kawasaki KZ700, with 9600 miles. Bike runs well
most of the time, including a fairly hard ride up a mountain.

However, after about 10 miles of high-speed interstate riding above
probably 60 mph, the bike just loses its gusto and has trouble keeping
up with traffic. I think I heard some knocking when trying to
accelerate. Pulling off the highway and letting the bike sit for a
moment allows it to regain its strength. It almost feels like one
cylinder stops firing, and its true that the rightmost exhaust pipe is a
lot cooler than the the other three. The plug was not fouled, though.

I was guessing either fuel starvation or overheating although I really
don't have a good idea. I suspect the bike runs slightly lean because it
has trouble starting on really cold mornings. Any ideas? The bike has
never had valve clearance checked (which I am going to do this week).
Oh, and the fuel petcock is new, and the strainer was clear.

On another note, what would cause my rear brake pedal to not return
after being pressed? the brake works, but the pedal is difficult to
press and it sticks down.

 

The valve clearances could use a check, though are unlikely to be the
problem. Could be a duff coil. They're well known for giving up the
ghost on these bikes, when they get old.

That'll be the brake pedal pivot where it goes through the footrest
plate or similar.

Remove pedal assembly, clean up, grease, and re-assemble, I had to do
this regularly on my old air-cooled Kawasaki 750.

 

As for the loss of power problem, check the wire going from the coil to
that particular cylinder. I know on my old honda 750, I had a similar
problem where all but one of the pipes would get hot and it turned out to be
the wire needing to be reseated at the coil.

Good Luck,

Fwed

 

Thanks for the reply.

If the coil wasn't firing that cylinder, why would it only be after high
speed riding? would the plug be fouled?

 

Well, if the plug were fouled, you would have problems from the get
go.....maybe the vibration given off at the high speed is enough for the
wire to misfire. On my bike, one coil fires cylinder 1 and 4, and another
coil fires 2 and 3. I am not sure if this is the same set up you have on
your bike. I found that at first exhaust pipes 1 and 4 were just getting
hot, so I knew it was something electrical. turned out I reseated both
wires for cylinders 2 and 3 and now the bike starts up right away and runs
like a champ (with the execption of a slight studder artound 5000 rpm. I am
thinking of increasing the main jets (4) from a 105 to a 107.5. Hopefully
that should take care of things, as its running a little lean and I already
have the screws turned out 2 1/2 or so turns.
In any event, check the plug wires.. .make sure they are properly
seated... or swap one with another one to see if the problem follows... if
it does, then you know for sure its in the wiring... if you have the same
problem, then like the older gentleman said, its probably a coil.

Fwed

 

While it might well be an ignition problem as others suggest,
first check out your carbs, fuel lines, & filters.
I had a similar problem once, marginal fuel flow, OK at low speeds
but passing from high cruise, or sustained high speed caused a drop
in float bowl levels with attendant knocking & loss of power.
I'd roll on, she'd respond and then just wimp out.
A brief stop would let the levels recover and the engine came back
for a while, similar to your description.
My problem turned out to be fuel lines damaged internally - looked
OK outside but cracked inside.
Look for dirty filters or clogged/kinked lines or dirty float valves.
( Dirt can be hard to spot on a wet screen and lines can be damaged
internally.)

As to the brake problem, look for a weak return spring or
binding in the pedal mechanism.

Best of luck,
MadDog
R75/5 Forever!

 

I repaired a Husky weedeater by replacing a plugged fuel cap. It would
run just fine, even at high speeds, but only for about 5 minutes, less
if the tank was almost full. As I removed the filler cap once, I heard
a sucking sound and realized that the brand new unit was bad.

 

I took a small engine shop class when I was a high school freshman. That
year I entered an Industiral Arts competition at a nearby university. One
of the competitions was to repair a booby trapped small engine well
enough to get it to run for 10 minutes. My instructor had prepared us for
most of the faults we would encounter, including a plugged fuel cap. It
was the only time I have ever seen that problem but it's still one of the
things I check when diagnosing a fuel starvation problem!

 

You ought to try opening the gas cap slightly. Could be lots of
other stuff, but occasionally a tank may not vent welll and form
a vacuum which can interfere with fuel flow. Not sure why one
carb would be more starved than the others unless it was at
the tail end of the fuel plumbing. You could also check the
plug for a healthy spark.

You might want to start by lubing the pedal pivot and if it's
a mechanical linkage, checking the springs. Is there
any component fouling another ? Anything bent ? Is it
assembled correctly ?

 

I will try that, thanks for the suggestion!

 

will do. Thanks so much for your help.

 

Let us know how you make out with this.... if you find the problem goes
to the cylinder you change your wires with, then you have a wire problem...
if not, then it could be coil. Another thing that dawned on me is it could
be the main jet in the carb for that cylinder. Main jets will kick in
around 4500 rpms or so and if that one is clogged, it may not be getting
fuel to the cylinder.... you can also switch main jets to see if the problem
follows, although i would suspect electrical first....

Fwed