GPZ600R Won't Start - Compression Issue

Oh shut the **** up you idiot...

 

It's the carbs. Gummed up, and he didn't clean them properly. Or worse
still, buggered them further in trying to clean them.

 

Cruel but succinct and accurate.

 

Try and make me shut up, you retarded midget.

 

Firstly, thank you all for the replies. To give you some more details
and to answer some of your questions:

1) The oil level is in the middle of the range of LOW – HIGH.
2) It is OK oil, not the most expensive and hasn’t been changed in
about a year.
3) It ran fine the last time it was out (and the time before that), no
issues. It does occasionally die once warmed up or kinda bog down and
won’t go past about 4kRPM ish. Then after a while it clears itself and
all is fine again (accompanied by some smoke out the exhaust).
4) I don’t believe it is stale fuel as I put brand new fuel in about a
month ago when I cleaned the carbs out. I also fitted an in-line fuel
filter at the same time.
5) I’ve stripped GPZ carbs about 3 times over the years, when I
suspect a fuel issue, and it has always run fine afterwards. This time
it has not but I believe I’m competent at the job. I did a more
thorough job than what I have seen mechanics do, which is a quick
spray of all the bits with carb cleaner and air hose. They are CV
carbs.
6) When I cleaned out the carbs I completely disassembled them,
cleaned out all the jets, passageways, etc will carb cleaner (the idle
jets were clogged). This includes all the little passageways, float
bowls, etc. Everything was very clean going back together, adjusted to
the settings they were at previously. Everything that needed it was
oiled (eg, throttle spring). Throttle butterflies were adjusted so
that they all open at exactly the same time.
7) I don’t believe leaving a bike on its side-stand will cause head
gasket failure, that would be ridiculous. I thought it may be a
contributing factor. Perhaps there was moisture around the engine that
freezed/thawed over the sub-zero winter. I don’t know, just thought it
might be a useful question.
8) My method to getting it started: Iginition (got good spark with
charged battery and new plugs), fuel (think this is OK due to new
fuel, smell of fuel, cleaned out carbs, in-line filter and it won’t
start n brake cleaner), so then looked at compression (found 2 low
pressure cylinders).
9) The valve clearances were adjusted by a garage about a year ago.
10) Have checked the HT leads go to the correct plugs, even double
checked with the wiring diagram.
11) Had a strong spark on all 4 cylinders.

Hope this helps.

 

Low oil level will not affect whether or not the engine starts.

The quality of engine oil will not affect whether or not the engine
starts.

That tends to indicate a carburetor problem.

Bluish white smoke coming at the exhaust indicates that the rings
aren't sealing or that the valve guide oil seals are leaking.

If the rings aren't sealing, the engine will smoke all the time.

Valve guide oil seals leak so little oil it collects in the combustion
chamber and burns off when the engine is first started.

Oil smoke is thick and it hangs around for a while.

White smoke that rises from the exhaust pipe and dissipates rapidly is
either condensation of coolant leakage into the combustion chamber.

If two adjacent cylinders have low compression that might indicate a
leaky head gasket, and a leak down test would prove if that was the
case.

An engine will start just fine on stale fuel. I've started engines
that had gasoline in the tank that was two or three years old.

The volatile fractions that help keep carburetors clean and non-
polluting also cool the combustion process and when the additives are
gone the engine will ping when it gets really hot.

One of the problems that confuses newbies is that CV carburetors don't
have a real plate type choke. They have cold starting enricher valves
which are opened when the "choke" lever or knob is moved to the ON
position.

The enricher valves are AIR valves which bypass the throttle
butterflies.

Air flow through the enricher passages causes enough vacuum to suck
fuel directly out of the float bowls.

But the throttle butterflies must be completely CLOSED when cranking
the engine with the electric starter.

One trick is to turn the master idle knob all the way
*counterclockwise* so the throttle butterflies are not open the least
little bit.

The engine should start and idle on the fuel air mixture which comes
through the cold start enricher circuit, even on a cold day, if the
enricher valves are fully open.

However, the starter jet is a hole in the bottom of the float bowl. I
hope you squirted carburetor cleaner through all the starter jets in
the float bowls.

Like I said above, turn the master idle knob all the way
counterclockwise and apply full "choke" and don't twist the throttle
when trying to start the engine.

Sometimes I've found it necessary to hand choke the carburetors by
putting the palm of my hand over the inlet of each carburetor in order
to get the engine vacuum to suck fuel up into the idle jets and idle
passages.

The last time I had to do that, the engine hadn't been run for 4 years
and I removed the carbs and cleaned them thoroughly.

There wasn't a lot of gum and varnish in the carbs, but the engine
just wouldn't start until I hand choked each carburetor.

 

Go jump off of Tower Bridge, you stupid cocksucker.

 

When you say it 'ran fine' at one time, I presume that it was generally
startable and rideable, even though not as powerful as it would be with
four good cylinders. Regarding points 3) and 6), it does seem that the
immediate starting problem is related to air/fuel mixture which is
pretty crucial (ie., roughly speaking, if the ratio is less than approx
12:1 or more than 17:1, it will probably be impossible to start):


a) Perhaps there are leaks in the intake manifold, especially if it's
the rubber kind that deteriorates with age and also can easily get
distorted with repeated carb removal and installation. Sometimes this
results in the low speed symptoms mentioned in point 3). If so, the
carbs might well have been adjusted rich in the past to make it run but
the leak is just getting worse. If there is a manifold air leak you
might find that turning the idle screws out even further will make it
start, although it won't idle very well once it's warm - this would give
further evidence of an air leak. Hard to find an air leak unless you
can get the engine started. I'd also double-check that the enrichment
circuit or choke (whichever these carbs use) is on. If there is a choke
plate on the air side that could be checked visually, if enrichener
passage you'd need to blow air or fluid through the carb orifices to be
sure. If one or more carbs has an accelerator pump that might need
checking to (usually service manuals say how). I forget the name but
sometimes there's another device on carbs that shuts off fuel when the
throttle is released at speed to avoid backfires.


(Possibly a leak-down test could show a manifold air leak but I'm not
sure it would be easy to notice in this case since we already have some
leaking cylinders.)


b) I would also double-check the idle mixture screws (slow jet) against
factory settings (ie., number of turns out), if you can find a reference
for that. Also make sure each one of the screws still has its spring,
washer and o-ring intact. Similarly for the floats (ie., level).


c) In spite of the apparent good visual spark, in case the ignition
components are marginal/weak, I'd try to set the spark gap to the narrow
side of the recommended range which might help in at least getting it
started so that you spray the manifold to see if it's leaking. Cross
your fingers that it's not just pickup coils going down hill because
that's a little harder to diagnose.


I'm pretty sure that most any of the Japanese four-cylinder bikes will
run after a fashion with only two good cylinders and can usually be
started in a couple of tries.

 

On 08/04/2011 4:56 PM, ` wrote:
....

Minor point - at least a few CV carbs do have a 'plate' choke, eg., the
ones on the 1982 DOHC CB750's.

 

All good points from what I've seen. (It took me a long time to learn
to ignore the advice of neighbours to try to start with WOT. Amazing
how so many people think a high-speed engine throttle setting is better
for starting which is necessarily done at low speed.)


Also, with four carb bowls, if they've just been installed after
cleaning, it can take ten or more start attempts just to get the bowls
filled with fuel.

 

I was talking about engines in general, not motorcycle engines. I was
an auto mechanic.

Something changed here. It was not 1920 30 years ago.

Yes, with solid lifters.

Can you actually read? It sat for a month, if that. But "I'm not doing
well", eh?

One month or less. Like I said, *read* the original post.

You don't pick your spots too well.

 

So what? I have seen it.

"Not a chance"? I don't know where you worked, but I worked in
dealerships (GM), and dealer mechanics see a lot of strange things
that get worked out before the cars start hitting the independents. GM
had this issue with one of their SUV's around 2005. I don't remember
which engine because it was a "foreign" vehicle - Chevy or GMC in a
Cadillac dealer. We took it in as a favor to the owner, called the
factory on a no-start problem, and that was the cause. Something to do
with tight clearances, and gasoline additives.

 

Once again, one month or less is not "months".

It is *an* issue. Or do you just shrug that sort of thing off? I mean,
what's a couple of dead cylinders, right? There's two more after all.

I'm sure you do, but probably not with engines & driveability problems
in general.

 

The bike sat for a month. Do any of you actually read the posts your
replying to? Or do you just fire up the mindless sarcasm when you
think you see an opening?

Right. **** the dead cylinders.

Gee, that hurts.

 

Have you replaced the plugs? If they're wet, or carbon tracked, it's
not going to start. It's more effective to replace than clean.

 

Well, Rabbit's Ninja does have a PRIME position on the fuel tap, so it
should be no problem to fill the float bowls.

What I see as the biggest problem here is Neil Murray (TOG) trying to
shit all over the thread (as usual), and if Rabbit doesn't know that
Neil Murray is an asshole he will be confused by his spurious
"adviceis"

 

It doesn't have two dead cylinders.

 

It doesn't have two dead cylinders.

Want a JCB for that hole you're digging?

 

I did. The mniddle of winter makes it worse. It's now sat for four
months.

 

It's the carbs.