83 GPz 750 A1 Suspect Carb/Fuel system issues.

Hi fellas

I have a GPZ750A1 with Mikuni carbs. The bike will fire for a second when I use a bit of aerostart/ether in the airbox, but won't turn over otherwise.

Now this bike is missing hoses on the bottom of the carbs, and fuel leaks out eventually when the petcock (vacuum actuated) is in the prime position.

The top of the carbs seem to be shiny as per pictures.





Things I've checked
Bike has a good spark.
I put my finger over the vacuum hose when hitting the starter and felt some air pressure there.
Gas tank has been cleaned as per process on this website.

An additional issue is that on the fuel line there is an additional tap and what I guess to be a fuel filter. Is this normal?



Alos, I only have a little bit of petrol in the tank. Do I need a full tank for the vacuum to work properly?

Thanks for your help.

Eeek, no replies...

I took pretty pictures and all!

It sounds like that the floats in the float bowl are stuck or are leaking. this is the cause of fuel leaking out

Do I need a full tank for the vacuum to work properly?
NO, because the vacuum from carb is supplied to open
the petcock and has no relationship to fuel level
inside the tank.

Other than that tidbit, my advice on CV carbs
would pretty much be guesswork. :lol:

The pretty pics show up large and clear,
but maybe too large for some viewer's setups
causing the text to run off the screen.

Might get a better understanding of the various
hose connections by studying the carb assembly
diagram on Kawasaki.com.

Good Luck!

Meanwhile, I'll guess a little until
better advice arrives --

Perhaps the fuel cutoff has been added because
the petcock isn't properly closing without vacuum.
This line would supposedly provide fuel from the petcock.

The filter is probably just an accessory
in-line fuel filter (and might be clogged).

The tube labeled "vacuum" in the pic
likely runs to the petcock.

And bigtime guessing that the nipples on
bottoms of float bowls serve as both drains
and overflows, and should have tubes connected
and routed to underneath the bike.

Let us know if any help is needed with the
Kawasaki.com site in locating the parts diagrams.

Good Luck!

Thanks for the replies.

I've made some progress by replacing the hoses and filling the fuel tank.

After priming the bike, I managed to get it to turn over for about 10 seconds(obviously very rough + smoked a bit) but it responded to a little throttle and behaved itself in general.

However, I have a couple of problems.

1: After inspecting the exhaust, there seems to be a pile of carbon powder about 1/8 inch deep on the concrete under the bike. May have shook loose during the start? I looked down the pipe with a torch and while it's clear for as much as I could see, I think it'd need a clean out. Any ideas on what it could be and how I could clean out an exhaust pipe? Its a 4-1 lazer.

2: I thought I'd take the carbs off all the same and seemed to OK as per the Haynes manual. However, the throttle cable locknuts seem to be very hard to get off. I am using a socket wrench, but am having a hard time getting it over the locknut becuase other bits of the carbs are getting in the way. Is there an easy way to do this?

LukeJ wrote:

...fuel leaks out eventually when the
petcock (vacuum actuated) is in the prime position...
put my finger over the vacuum hose when hitting the
starter and felt some air pressure there...
have a little bit of petrol in the tank.
Do I need a full tank for the vacuum to work properly?...

Petcock in PRI (prime) position allows fuel
from the petcock without needing vacuum.
Other positions need vacuum
to allow fuel from petcock.

Vacuum hose goes to petcock, whereby
vacuum from running engine supposedly
opens petcock to allow fuel from petcock.

As fuel level inside the tank goes down,
eventually it becomes necessary to switch
the petcock to RES (reserve) position,
which also depends on vacuum.

With petcock set on PRI allowing fuel
to flow into the carbs without vacuum
(i.e., without engine running),
fuel leakage is likely due to incomplete
sealing of the floatneedle in its seat,
often due to grit or crud in the seat orifice,
(as earlier suggested by mrsj).

Good Luck!

LukeJ wrote:

...After priming the bike, I managed to get
it to turn over for about 10 seconds(obviously very
rough + smoked a bit) but it responded to a
little throttle and behaved itself in general.
However, I have a couple of problems.
1: After inspecting the exhaust, there seems
to be a pile of carbon powder about 1/8 inch
deep on the concrete under the bike. May have
shook loose during the start? I looked down
the pipe with a torch and while it's clear
for as much as I could see, I think it'd
need a clean out. Any ideas on what it could be
and how I could clean out an exhaust pipe?
Its a 4-1 lazer.
2: I thought I'd take the carbs off all the same
and seemed to OK as per the Haynes manual. However,
the throttle cable locknuts seem to be very hard
to get off. I am using a socket wrench, but am
having a hard time getting it over the locknut
becuase other bits of the carbs are getting in
the way. Is there an easy way to do this?

Would not bother with trying to clean out the exhaust,
as it will likely take care of itself once the bike
is up and running.

Should first assure all ignition components,
compression and valve clearances are up to specs
before fooling with the carbs. Otherwise,
just wasting effort and risk doing more harm than good.
Ignition might be okay because
of the reported "good spark."
Meanwhile, would spray the locknuts with PRBlaster
or Kroil (or similar penetrating oil).

Would sniff-test the crankcase oil to help determine
whether any of the fuel leakage has gotten into
the crankcase.

Good Luck!

OK, valve clearances all line up fine as per manual.

Going for the carbs now to get the floats off.

There doesnt seem to be much room to remove the carbs as the airbox is in the way. Does the carb assembly just pull away from the rest of the engine?

All the bolts and nuts are undone and the throttle cable isnt attached.