Bike won't start after carb cleaning.

Hi all, back again with another sport bike - this being a classic, a
83 Kawi GPz305, belt drive - the forerunner to the Ninja and all the
fast toys today, and a treat to ride. Well, at least it should be if I
can get it going again.

Got this little guy recently, it had been parked outside and neglected
by the owner. Great fixer upper and already looking great, as
everything is in place and will make a superb bike for the wife.

Here's the problem and I'll provide as much detail as possible, so be
prepared for a long read. This is quite a puzzle.

When I first got the bike it would run but mostly off one cylinder. I
could tell that the left pipe (just off the engine) was hot while the
right pipe was barely lukewarm. I tested the sparks and it was
sparking fine on both cylinders (even put on new spark plugs). A
friend said it clearly was a clogged carb, which I agreed. At this
stage the bike would start very nicely, very easily. I had just put a
new battery in it and it started like a new bike, despite the obvious
lack of fuel to both cylinders.

So the next step was to take off the carb for a complete clean. Took
everything apart, inspected all the jets, needles, diaphragm, etc.
Everything looked great after a good cleaning, as it had varnish and
what appeared to be green sand everywhere. As it turns out the petcock
was defective and even though the owner thought the fuel was off, it
wasn't. So for over a year fuel kept on going through the carb. Ouch.

Btw I did not remove the carbs off the rack, just opened them up on
both ends and cleaned it completely. I used Yamaha's Combustion
Chamber Cleaner which is supposed to be a better form of carb cleaner.
Used a toothbrush and carefully cleaned every corner, every jet, every
tiny hole I could find.

Put carbs back on bike and it wouldn't start easily. Drained the
battery (again, brand new) to the point where I had to use my car to
boost it. After some effort it did fire up but run horrible. Idle was
all over the place, inconsistent and very rough.

Out comes the carbs again, for a second cleaning and a total
inspection to ensure I hadn't miss anything. Back on the bike goes the
carbs. This time it started a bit easier (with choke full on) and it
run beautifully. Although I had to have the choke on for several
minutes, the engine sounded great and idle was consistent. After
warming it up nicely, I was able to lower the choke till just past the
halfway mark. Any lower the engine would die. At this stage all seemed
well, I would turn off the engine and the bike would fire up nicely
with a brief press of the start button. Bike run through the gears
fine and seemed to have plenty of power. All seemed well and fixed. I
kept on riding the bike around the block till the engine got nice and
hot. Perhaps too hot? Cause at one point it just died, like it had a
few previous times while running and you just knew that it would be a
bitch to start again.

After waiting till the engine cooled, I attempted to start it again.
No go. It turns fine and sounds good, it just won't fire. I'm trying
to start it with a boost from my car (car running) and no go. I have
the choke full on and everywhere in between. I have the air screws set
from one turn to 2.5 turns out and this too didn't help. Spark is nice
and strong on both cylinders. I know the carb is getting fuel as I see
it in the float bows (after draining it). All systems seem fine but
the thing just refuses to start. The puzzler is, when it does start it
seems to run great (albeit with the choke still on and some backfire
due to this) till it gets hot and dies again. Except that now I can't
get it to start at all, even with a boost from the car and several
minutes of trying.

Is there a trick to getting this bike to start nicely again? Remember,
prior to me cleaning the carb it would start nice each time so I don't
think it is a starter problem but it points more to a carb issue. I
didn't play with the float bows as they seemed fine and level. The
throttle and choke butterfly all seem to open and close at the same
time. The diaphragm seems good and rides up and down nicely. In fact
the whole carb looks good on the inside. I suspect I may have to pay a
mechanic to adjust the carbs but I wonder if there is some minor
adjustment I can make in order to get it to fire up the bike. I mean,
since it seems to run well when it fires up, it makes me think that
the carbs are pretty close to being sync'ed.

This is driving me crazy. Please help.

 

You didn't mention cleaning the tank/screens and/or installing a fuel
filter.
The carbs may be plugged up yet again.
The stopping after heating up may be a plugged gas tank vent........or an
ignition part failing when hot.

 

Guess I wasn't as detailed as I wanted: yes, I did clean the gas tank
inside as it had tiny specs of rust. I also removed and rebuilt the
petcock (since this had a worn out o'ring and wasn't sealing) and
ensured the fuel filter is clean. So I don't suspect that more dirt
got into the carb. The second time I took the carb apart and cleaned
it, it didn't have any more dirt in it.

Someone suggested soaking the carb in cleaner overnight. I did not do
this as I thought I could just clean it with a toothbrush. Could a
small amount of varnish or dirt be present in some tiny passageway and
could this be the cause of all my headache?

 

Eat Dirt wrote:
....

I'm not as expert about carbs as some here, but I know that for sure the
little jets and float passages can easily have gum or dirt that you'll
never see if you don't at least blow them out. I use just a very small
air compressor for that, but if I have the carb off always soak first.
One guy uses Pinesol to soak his carbs with, but if a soap is used
you'll want to be sure to blow dry very thoroughly. Some people just
use one of those air tanks you can fill at the gas station and some even
use the air in their car tires! I guess there might be enough air in
the bike's tires to blast a passage or two for a few seconds. That's
what I'd try as long as I had a bicycle pump handy and I'd probably be
less unfit to boot.

 

Yes, possible. The compressed air suggestion is also good.......just
protect your eyes. Carb cleaner STINGS!!

 

I'm sure. Maybe toxic would be a better description since I don't think a
few drops (applied anywhere) will KILL you.......or even make you deathly
ill.

 

Your idle jets are all plugged up. Remove the idle mixture screws and
spray Berryman's B12 or STP or GumOut carb cleaner through all the
idle mixture ports, including the three acceleration transition ports
located near the lower edge of the throttle butterflies.

The engine draws fuel through the idle jets and air through the pilor
air jet which may be in the inlet bell or under the rubber diaphragm.
Then the mixture goes off to the single idle mixture port behind the
idle mixture screw and to the three acceleration ports.

Spraying carb cleaner through the pilot air jet and the idle jet
should result in a strong stream of fuel air mixture coming out of
each port.

I cannot advise you as to how many turns open your idle mixture screws
should be, because it depends on the area of the orifice in the idle
jet, and the area varies exponentially as to the square of the radius
of the jet.

Some bikes have tiny idle jets, like #30 to #35 and they need the idle
mixture screw to be turned out 3 to 3-1/2 turns.

Other bikes have huge #40 to #45 idle jets and the idle mixture screw
only needs to be turned out 1/4 of a turn.

When starting the motorcycle, the choke should be fully "ON" and the
throttle should be fully closed to avoid uncovering the three
acceleration transition ports, which makes the idle mixture far too
rich.

 

Thanks, I did what you said and I have cleaned the air mixture screws,
which were indeed dirty. I also fully cleaned each and every tiny hole
by spraying carb cleaner through them. Now I feel that this carb is
fully clean. But I suspect I found a problem: my diaphragm and its
cylinder may not be working as it should. What do you think of this?
The manual says that in order to test it, I should place the carb
upright, cover the inlet air hole, push the cylinder way up and time
it as it slowly descends. It claims it should take over 10 seconds.
Well, in my test one of them took 6 seconds while the other only took
3 secons. Is this bad? I hope I don't have to replace these as I
suspect they'd cost a small fortune. But could this be causing
starting problems and causing the bike to run lean as well?

I plan to install the carb back on the bike later tonight to test it.
Although I'm now wondering if I'd be better first bringing it to a
mechanic to properly adjust the float levels. The bike is clearly
running very lean (white spark plug contacts, overheating, need for
the choke to be on, etc). Do you think this to be a good idea too?
Thanks for the help.

 

If it runs OK cold but dies when hot, sounds like it's rich,
though I can't tell from your description whether the choke
is still on or not.

If I had to make a bet, I'd wonder if you got the choke
back together right. When if gets hot and dies, what
color are the plugs ?

As a suggestion, it's really good to separate your
description of the symptoms from your description
of what you did to the bike.

Both descriptions are useful, but it'd hard to sort out
when you keep mixing the two of them together in the
same paragraphs. Separate lists of symptoms and
what you did would probably help you to get a better
handle on the problem as well.

 

Well ya, if you drink the stuff, so is gasoline! ;-)

 

A leaky rubber diaphragm will not affect starting and idling, but the
engine will not accelerate once the throttle is opened.

You're right, diaphragms are expensive, about $100 each from the
Dedicated $tealer$hip, but riders have been ordering aftermarket
diaphragms from some place in England.

It still sounds like your idle passages are plugged up, or there is a
fuel starvation problem somewhere in the system.

You might have an intake air leak, or the intake valves might be
adjusted too tight. When this happens, the engine blows hot air
backwards through the carbs and the engine runs very lean. I saw this
happen on my pickup truck once...

If you have the specifications, it's easy enough to adjust the float
level by bending the tang that goes against the pin on the fuel
shutoff needle.

Float adjustment is done with the carbs upside down on the bench, and
the tolerance is plus or minus 1 millimeter.

Say the specification is 14 mm. Since the carbs are upside down, 13 mm
results in a high fuel level and 15 mm results in a low fuel level.

Some carbs have a tiny fuel filter above the needle jet seat and this
may require disassembly on carbs with screw in needle jet seats. Other
carbs have pressed-in needle jet seats, but you can backflush the fuel
inlet by spraying carb cleaner through it opposite the direction of
normal flow.

 

Not sure how a thread about a bike not starting turns into an idiotic
debate on how sniffing carb cleaner to kill you and cause your wife to
give birth to a 7 headed monster but for those that actually tried to
help, here's an update:
Installed the carb after a 4th attempt at cleaning it - and the thing
fired right up! Wow, I couldn't believe it. It's like a new bike now
and works absolutely well (despite being too lean). Here's what I
think happened (for those thread jackers that have a hard on for carb
cleaner you'll like this). I had initially used Yamaha's combustion
chamber cleaner to clean out the very gross varnish and greenish sand
that was the inside of both carbs, due to a friend's recommendation. I
noticed that it left a somewhat thick, very shiny and slippery residue
on everything it touched. I figured that gasoline would just clean
that out once gas run through it. Well, it actually didn't. A guy at
local shop said that some of the jets need to be exceptionally clean
as it is very sensitive to anything (the jets responsible for idling
and starting). Suspecting the combustion cleaner was the problem, I
picked up a can of carb cleaner (thread hijackers, pay attention) and
completely cleaned everything over again, leaving a dry, crisp
surface. I also sprayed it through every hole, which inevitably
backsprayed onto my eyes and face. Guess what folks: I can still see
and despite even tasting it, I managed to survive.

I still have one problem though: bike is still running too lean. I
have set the air screws to only half a turn despite the manual
recommendation for 1.75 turns from completely closed. I figured that
by letting less air in that it would richen the mixture. Well, I still
get a whitish spark plug and I noticed the engine seems to be running
very hot even though this is an air cooled bike and the bike was
mostly idling in place. However I no longer need to have the choke on
for the bike to idle, which is a sign that I'm on the right path.

What can I do to richen the mixture? I don't think replacing the jets
to be the answer as previous to my carb cleaning the bike was running
properly, as seen on the old spark plugs that looked 'normal'. Any
tweaks I can do?

 

Hmm, I wonder if that's the problem then for my bike being too lean
now. I never did bring the carb to have the float levels adjusted
(since it requires a special fluid level tool) and just left it as is.
But I did play with one of the floats. Here's why:
When I first took the carb apart, I noticed that the right float
wasn't lining up with the left. It was some 2mm off from the left,
although I don't recall if it was lower or higher. Since the left
cylinder appeared to be working properly (as it was getting fuel when
I first tested the bike) I bent the small tab on the right float to
make it level with the left. Could this have leaned the mixture too
much? If so will it be a good idea for me to go in there and change
the level by a couple of mm?

If so, please describe the process again. Since I want to richen the
mixture I suppose I want more gas in the float bowls right? So does
this mean that I should lower or elevate the level as I have the carb
upside down. Thanks for the reply.

 

Hey Mark, no I am not sure. I am assuming that it is air screw since
this is what most bikes have. But if your GPz550 have fuel screws,
then by golly, I had it backwards! The manual I have doesn't mention
what it is, except that it is a mixture screw. Doh, how useful is
this?!

Hmm, you may just have saved me from taking the carbs out and playing
with the float levels. I will turn it another 1.5 turns or so and see
how it goes. Thanks a bunch!

 

Follow your manual's recommendation for initial setting of idle
mixture screws. As I said previously, it's hard to give a rule of
thumb for GAS screws, because the area of an idle jet varies
exponentially as to the radius of the orifice hole.

The range of adjustment can be anywhere from 1/4 of a turn off the
seat with larger # idle jets ( #40 to #45) to 3-1/2 turns of the seat
with smaller # idle jets (#30 to #35).

Normally, an idle mixture screw that is downstream of the throttle
butterfly controls previously-mixed fuel and air and is regarded as a
GAS screw.

Turning a GAS screw counterclockwise richens the idle mixture and this
has effect from closed throttle until the throttle
is wide open.

Idle mixture screws that are on the air intake side of the carb are
AIR screws, and turning them clockwise richens the idle mixture.

 

You can buy a cheap plastic caliper to measure the distance from the
float bowl mating surface to the bottom of the float, which is on top
with the carbs upside down on the bench.

If you bend the tang so the dimension from the bottom of the float to
the mating surface is smaller, the fuel level in the float bowl will
be higher, making it easier for engine vacuum to suck fuel into the
idle circuit.

If the float level is more tham 1 mm higher than recommended, the
engine will idle too rich, and if the level is more than 1 mm lower
than spec, the engine will idle lean.

 

Thinking about it now, it is a Keihin carb (not TK) and the screws are
position on the half of the carb that is closer to the air box and not
the front of the engine. Guess this means I have air screws and not
fuel screws, right?

 

You're lucky. That was a pretty stupid move.

Yes but what makes you believe that the screw you are turning is regulating
the AIR?
I propose that it is the gas you are adjusting and more turns out = more gas
= richer mixture.

After that, you need to look for an air leak BEHIND the carbs.....like a
loose or cracked boot.

Are you doing this (mostly) without the air cleaners on? Many bikes require
a slight restriction in the incoming air to achieve the right mixture (all
things being stock,that is). Without that, they are too lean.

P.S. You might want to be a little more careful about who you berate. They
might end up actually helping you out.........if you don't piss them off too
bad.

 

Mark.....hello Mark.....are you with us now (looks like you weren't when you
wrote that).

The float level will NOT affect the performance of the engine, unless and
until it is WAY out of adjustment. There is a fairly wide range over which
you won't notice any difference at all, as it does NOT change the mixture.

 

Total bull shit.
A difference that small will have no impact on the mixture AT ALL.