GPZ600R Won't Start - Compression Issue

Hi.

I have a 1985 GPZ600R that doesn’t want to start. I put it away just
before Xmas and it wouldn’t start again in January. I have charged the
battery, put a backup one in parallel, cleaned out the carbs, put new
fuel in the tank, tested the spark (big blue spark when against
engine), replaced the spark plugs, checked the engine isn’t seized
(can be turned over from rear wheel in top gear). I have also tried
using brake cleaner, carb clearner and easy-start in the engine with
the air filter removed. It currently turns over but does catch/start.
I am convinced the ignition is OK as the spark looks healthy.
Similarly, I believe it is getting fuel as I can smell fuel from the
exhaust pipes and it goes bang/backfires if I try to start it for too
long.

I have not checked the exhaust for any obstructions but can’t see how
this could happen it has been stored in a garage). I haven’t checked
the timing, alternator, starter motor, CDI or reg-rec but don’t see
how they could be an issue. I have I also haven’t tried bump starting
it as it is flat where I live and I don’t think I’d get enough speed
up. I ran a compression test this evening:

Compression Test

Method: Ran the engine cold and with a Wide Open Throttle (WOT). I
used another battery in parallel with the bike battery to ensure there
was enough power. Tested each cylinder 3 times and then moved onto the
next from 1 to 4 (left to right). To ensure the numbers were reliable
I then retested the cylinders (again from 1 to 4). As the readings
were very low for cylinders 3 and 4 I put a bit of oil in these
cylinders and took 2 new readings. When taking the readings I did so
after about 8-10 cycles as it was usually still rising after about 5
or 6. My results (all in psi) are as follows:

Cylinder 1 – 138, 138, 142 – Average 139
Cylinder 1 Retest – 140

Cylinder 2* – 130, 122, 135 – Average 129
Cylinder 2 Retest – 142, 140, 145 – Average 142

Cylinder 3 – 80, 82, 89 – Average 84
Cylinder 3 Retest – 91
Cylinder 3 with Oil – 108, 110 – Average 109

Cylinder 4 – 30, 29, 30 – Average 30
Cylinder 4 Retest – 35
Cylinder 4 – 48, 48 – Average 48

* On cylinder 2 I originally recorded 90, 100 and 105 but then changed
to another backup battery as it was running out of juice. The fresh
battery gave the numbers given above. Why does the strength of the
battery affect the compression reading? Is it due to the greater
inertia of a faster moving piston?

In summary:

Cylinder 1 – 139psi
Cylinder 2 – 129psi
Cylinder 3 – 84psi
Cylinder 4 – 30psi

As I understand it this could mean three things:

1) The head gasket has failed on the right-hand side of the engine as
the values slope that way. Could this be due to the bike being parked
on its side-stand for an extended period (oil starvation of some
kind)?
2) The piston rings in cylinders 3 and 4 are worn and require
replacing.
3) Adding oil to cylinders 3 and 4 did not bring back sufficient
compression, so a valve service (lapping valves to give a better seal)
is required. Would adjusting the valve clearances give any benefit?

Can anyone confirm my diagnosis and recommend where to go from here? I
imagine a leak-down test would be beneficial to pin point the exact
source of the lack of compression.

Any advice would be much appreciated. Thanks.

 

You're right that a leak-down test it the next step. Anyway, if it's
valves, if it has hydraulic lifters, it could be insufficient oil
pressure to the lifters to open the valves. If that's the case there
will be no leak-down. Maybe excessive oil pressure holding them open.
Maybe deposits on the valve stems, again holding the valves open. Did
you check the oil level? Is it good oil? Also, did it run okay the
last time it did run?

 

Learn to snip....

Someone with this much ignorance of the bike in question shouldn't
really be trusted, IMHO.

Not a problem since about 1920.

<Holds head>

 

<Snip the rest>

One cylinder does look rather low, and one looks worryingly low, but it
should start anyway.

Your problem is stale fuel in the carbs; jellied fuel that's blocking
key passageways and jets.

If you dismantled the carbs yourself to clean them, the chances are you
made the problem worse unless you *really* know what you're doing.

And this:

it due to the greater inertia of a faster moving piston?

makes me worry. As does your worry that leaving a bike on a sidestand
could cause a head gasket to fail.

Look, get SWK to strip down the carbs properly. Best solution is
ultrasonic cleaning, but proper professional-style cleaning plus
cleaning out all the jets with tiny strands of copper wire and lots of
compressed air will, if you're patient, do the job.

Don't start tearing down the engine.

 

So I guess you missed the "if" in my reply?

It still happens on cars, so why not bikes? Reminds me of the
"ignorance" comment.

As am I. Sarcasm work best if you know what you're talking about.

 

That explains what is essentially no compression in one cylinder? That
is an issue that needs to be addressed, don't you think? BTW, if you
had actually read the initial post, he said the bike sat for about a
month - that's all. Stale fuel? That's an interesting theory.

Right, that should get the compression back up.

As they say, when the only tool you have is a hammer, every problem
looks like a nail. I guess when you have some special carb cleaning
aptitude, that's where the diagnosis always leads.

 

I'd agree about the compression being a bit of a red herring, ie., if
everything else is okay it should start even though it would probably
run roughly. (eg., it should start even if the carb to cyl #4 is
blocked off.) But the OP didn't state whether he has ever been able to
start it so for all we know the plug wires are connected to the wrong
cylinders or the carbs are massively out-of-sync or the choke/enrichener
is not adjusted or a few other things. I'd say the only useful result of
a leak-down test, at least as far as getting the engine started is
concerned, would be to confirm that the valve timing hasn't been
reversed by somebody who's had it apart. The OP did say he had clean
gas but as you suggest the slow jets could still be blocked or the carbs
seriously mis-assembled after cleaning (the OP didn't say whether the
carbs are the slide type or CV type but either way it's not hard to muck
things up when there are four of them). Also, he didn't say whether he
had spark on the cylinders that have decent compression. Still, I'd
agree that it is kind of a waste of time to do a leak-down test when the
immediate problem is getting the engine started.

 

If (hah!) you have to speculate, you *really* don't know what you're
talking about.

It is *such* a rare thing to happen on bikes built in the last 30 years.
The 'excessive oil pressure' thing we can safely discount. You're not
doing well here.

Apply Occam's Razor. The bike has been sitting for nearly four months.
It's reasonable to assume it was running before "it was put away", or
the OP would have said "it hasn't run since x", but it's not a given, I
grant you. Still, if it has been sitting for *longer* that only makes
the stale fuel likelihood even more likely.

And you don't. Now, apologies for being curt, but there are times and
places when...

 

It seems to be the case. nine times out of ten, when somebody has left a
carb-fed[1] bike sitting for months without using it. A simple Google of
this and other groups will show you that.

The compression isn't the issue here. It really, really isn't.

I don't. But I've got a bit more experience with bikes than you have.

[1] Less of an issue with FI. I wonder if you can work out why?

 

All sniping and lack of snipping aside, have we determined whether or not this
engine actually has hydraulic lifters? If we're dealing with solid lifters and
adjustable tappets, it's entirely possible that two cylinders have tight valves
causing low compression.

And it's entirely possible that it was left sitting with 10% ethanol fuel in the
carbs, which has dried out and left the idle circuits plugged. Many bikes will
not start if the throttle is not at idle position (none of mine will), so if the
idle circuit is plugged, it's not going to start at idle position and opening
the throttle during cranking will not help.

It would help if Rabbit would come back and tell us exactly what he did when he
"cleaned out the carbs".

 

FFS. Yes, we have. It doesn't.

Irrelevant here due to above.

Yes, you're right on the money here. Ethanol fuel or not, the carbs are
gunged.

And on the money here, too.

 

<snip>

Just for the record, a minuscule percentage of Japanese bikes have or
have had hydraulic tappets.

A few big cruisers and HD-wannabes. I think later iterations of the Gold
Wing did. And the Honda CBX750 and its variants (Nighthawk, etc) did. A
tiny, tiny percentage.

 

It most defintely does not have hydraulic lifters or lash adjusters. Without
looking at the fiche, it's either screw and locknut adjusters or shim under
bucket... OK I cheated, it's screw and locknut, and the forked rockers look
identical (but they're not) to the ones used on my ZG1000. It's possible that
the clearances closed up and the the valves burned, I suppose.

Very likely. As others have said, while the low compression on #4 is a concern,
presumably when it was put away it did run, however poorly.

Since I do have a homemade leakdown tester, I would definitely use it, but they are
available to all, for not too much money (< $40) at your local cheap chinese crap
store, and using one will definitely help to find where the compression is being
lost:

http://www.harborfreight.com/cylinder-leak-down-tester-94190.html

Agreed.

 

In my 30 years working on cars NEVER has a deposit on a valve stem held a
valve open. carbon on the valve face yes, stem Not a chance. KB



so why not bikes? Reminds me of the

 

If the clearances haven't been checked for yonks, yes. Or if someone
cocked up the adjustment. As you imply, though, the low compression is a
red herring here.

It's the carbs. It's always the carbs.

 

(The Older Gentleman) wrote in

your so sure its the carbs, why won`t it start on either then, he did
say he tried it!!!!!!!!!!!!!!! doen`t make sence to me. KB

 

No, I'm sure it doesn't. Don't lose sleep over it.

 

By all means, check the valve clearances before you remove the
cylinder head to do a valve job.

The 600 Ninja has simple screw type valve adjusters, so you don't need
to remove the camshafts to adjust valve clearances.

Did the engine smoke on start up and stop smoking after it warmed up
before you stored it for the winter?

Smoking on start up is a symptom of leaky valve guide oil seals and
oil that leaks down onto the valve head will turn into wet carbon that
will block the intake valves from closing, thereby causing a loss of
compression.

The exhaust valves run a lot hotter than the intakes, so they burn oil
off the heads of the valves.

But my GS1100's intake valves actually burned and pitted because of
leaky valve guide oil seals.

The easiest way to remove this carburized oil from the valve heads is
by a *shock treatment* of Techron Concentrate in the gasoline.

Techron is a copper chemical that prevents carbon from attaching
itself to the intake valves.

 

True, but it's another strike against the engine starting without correcting
anything. If either of those two cylinders have a functioning idle circuit, it
would help if they had any compression.

Unless it's something else. Crosswired, a mixture of brake cleaner, ether, and
Ged knows what else sprayed into the intake, tight valves (not necessarily
burned - yet) ... ;-) Head gaskets don't normally fail sitting in a garage.

One of the hardest to correct operator errors I ever saw was on my own bike, a
Suzuki DR250. Someone who should know better was trying to start it by rolling
on the throttle as he thumbed the starter. Got it so flooded I ran the battery
down trying to correct it and had to bump-start it, it rolled a good 100 yards
before it ever fired. When I got it back to the house, he said "Interesting
starting procedure. What do you do when you're not on top of a hill?" I shut
off the ignition, turned it back on, and touched nothing but the start button.
Fired right up.

RABBIT? What exactly, step by step, did you do when you cleaned out the carbs?
Did you take the whole carb bank off the engine? Did you separate the carbs
from each other? Did you have any parts left over? Have you had more than one
plug wire off at a time?

 

Yep the compression is a worry BUT it wont keep it from starting.
Stale fuel? Interesting theory? Sir you are either sarcastic or a
blithering idiot...frankly from what you've posted so far I'm inclined
to believe the latter and call bullshit if you claim the former.

The compression means **** all if it isn't running.

And you madam are a TOOL.