Open throttle starting

I have a 2000 Katana GSX750F that has been acting up. A couple
weeks ago, I rode it home from work and it wouldn't start half an hour
later. I had to let it sit for a few days until I had time to take it
apart. In this time, the full tank of gas leaked out.
When I got the airbox off, it was full of Gas. I was told a stuck
float was to blame. I tried to take the float bowls off but they are
held on to the 4 Mikuni carbs with 4 aluminum screws each, that I
couldn't get off without stripping. So, I switched plans and sprayed
an aerosol carb cleaner in all the orifaces and fuel rails and let it
soak overnight.
The next day I put the carb back on and it started great. Well, I
ran it idling for a few minutes then shut it off and checked the oil.
Thank God I didn't ride it because the oil was full of GAS. I assume
it went down the open valves and leaked around the pistons.
I changed the oil, and filter, and I have a new air filter on order
(the old one was saturated with gas). I also put a cap full of oil in
each plug hole to try and lubricate the pistons that I assumed had gone
somewhat dry with so much gas in the oil. I'm putting a can of Sea
Foam Carb Cleaner in the gas now. Half a can for a full tank (about 5
gallons). Hopefully that will get the rest of the crap out of the
carb.
I thought this took care of it but now it is starting to have the
same symptoms as before it quit. When I start it, I have to open the
throttle at least half way before it will fire. Then it sputters to
life for about 4 seconds, the carbs catch up and it revs. After that,
the bike runs great, throttle response is improved from the cleaning
(long overdue as gas sat in it for the year I was overseas).
So, my question is, should I be worried about the open throttle at
startup? As I understand CV carbs from books and taking mine off,
Opening the throttle only allows more air through and that airflow
opens the needle valve. So, does the throttle have to be open to get
enough airflow to pull the fuel out of the main or shouldn't there be
an Idle jet? I noticed my idle speed adjustment just limits the
butterfly from closing all the way, so is there an idle jet?
It runs, so I'm not likely to take it apart any time soon (unless
it quits again) but i was hoping someone could explain this phenomenon.
Thanks for the help.

Tim

 

This happens fairly frequently.

I tried to take the float bowls off but they are

You need to use a #2 Phillips screwdriver and push HARD while you are
turning the screwdrover with great force to loosen those screws. They
come loose with a SNAP that sounds like you broke something.

That's a good way to loosen up stuck float valves. Berryman's B-12
Chemtool Choke and Carburetor Cleaner works good to unstick float
valves, it contains xylene, acetone and methyl alcohol.

Yes, it happens, and it's possible to have a crankcase explosion from
gas in the oil. That would probably blow the rubber plugs on the ends
of the camshafts out.

There is probably so much gasoline still in the engine you need to open
the throttle to get enough air to blow it out. Or the float valves are
still sticking and the fuel level in the float bowls is too high.

Bzzzt! Nice try, but no cigar. When you're cranking the engine with the
starter, it doesn't develop enough vacuum to lift the slide valve high
enough to raise the jet needle out of the needle jet to the point where
the tapered part is coming out.

Constant vacuum carburetors don't run on the main jet until the
throttle butterflies are wide open and the jet needle is raised all the
way out of the needle jet. The main jet has nothing whatever to do with
starting your engine.

Yes, there is an idle jet in each carburetor and it is more important
than the main jet. Constant vacuum carbs have HUGE idle jets, because
the engine is running on the idle jet 90% of the time.

The idle fuel is sucked into the idle passages through the idle jet.
The idle air is sucked into the idle passages through the pilot air
jet. The idle fuel and idle air mix. Then there are four outlet
passages. Three of the outlet passages are just downstream of the
throttle butterflies. They are called transition ports. As the throttle
opens, it uncovers the transition ports, allowing the engine to get
extra idle mixture for acceleration at 1/8 to 1/4 throttle.

There is a fourth idle mixture port about an inch downstream of the
transition ports. It is regulated by a tapered idle mixture screw that
acts as a trimmer on the idle mixture port.

You probably cannot see this screw on the underside of the carburetor
just forward of the float bowl because it is concealed by an EPA
anti-tamper plug. If you can see the slotted end of the idle mixture
screw, that means some shade tree mechanic has drilled the EPA plug
out.at bowls

Depending on the size of the idle jet, the correct setting of the idle
mixture screw may be anywhere from 1/8th of a turn open to about 3.0
turns open. All the idle mixture screws on my FZR-1000 are set 1/4th of
a turn open, because the idle RPM will run away when the engine is hot
if the idle screws are open 1/2 a turn.

Shade tree mechanics always open the idle mixture screws too far,
expecting the idle RPM to increase. When the idle RPM decreases
instead, they set the idle RPM higher. This causes hard starting when
the engine is cold and the idle RPM will be too high, or even
uncontrollable when the engine is hot.

Then the shade tree mechanic parks the motorcycle, the gasoline
evaporates out of the float bowls and the shade tree mechanic sells to
motorcycle to a newbie, saying that the carbs need rebuilding or
something, he's not quite sure of how he screwed the carburetors up.

Since your motorcycle has probably sat unused for a long time, the
gasoline in the float bowls evaporated, gumming up the float valves.
The idle passages and idle ports are also probably plugged up, so you
need to spritz them out thoroughly.

Your engine should start on full "choke" and fast idle without touching
the throttle grip if the idle passages are clean and the idle speed
screw is set correctly.

Constant vacuum carburetors do not usually have a real choke with a
plate. Instead, they have a starting enrichener valve which opens a
bypass air passage around the throttle butterflies. There is a passage
to the float bowl and when the enrichener valve is opened, the engine
sucks gas straight out of the float bowl.

Opening the throttle just reduces vacuum in the carburetor and less
gasoline is sucked out of the float bowls, so leave the throttle alone
when starting the engine, unless the engine is flooded with gasoline.

Constant vacuum carburetors are mysterious gadgets. It took me 30 years
to figure out what was going on with them.

 

All the time that is why you have a petcock on the bike, use it.

Don't do this it's a great way to ruin those screws.

Instead buy an impact driver from any tool place, the kind
you hold and hit with a hammer. You don't need to whale on it
with the hammer, just a single tap will do it. Use a screwdriver bit
and adapter for it. The tapping is far more effective to break the
screws loose and it doesen't get the heads all sharp and deformed.

Ted

 

You might even try a right angle screwdriver. I have one made by Stanley
that is very good.

Add to that the fact that while they look the same, the Japanese phillips
and the American phillips heads are different beasts. The difference is
subtle but in the case of tight screws, it can be quite frustrating. Do
some google research and you will see what the differences are. It is
helpful if you tap the screwdrive into the screw before trying to remove
it. DON'T let it slip and round off the interior corners of the screw.
That is death. Try various phillips screwdriver. IIRC Snap-On machines
their screwdrivers so that they offer a compromise between the US and Jap.
standards.

There are more versions of the "Phillips" type screw head than you can
imagine. Cross, Posi-Drive, Deck-Mate, are just a few and there are many
more.

Good luck.

 

Engine full of fuel - Info on screwdrivers.

I suspect that if your engine is running very rich that
it will get ruined due to oil being washed
off of the cylinder walls. You should make sure that
it is sorted out.

I once wrecked the crank bearings of an engine that had I believe
been sabotaged. The sump in any case had a lot of water in it
and I started it up. not knowing this.

I only ran it for a short time and did not drive it but IIRC there was
quite a bit of damage to the bearings.

I had just bought the (non road use) vehicle and did not lose on the
deal in any case.

Thanks for he bit on screwdrivers. The Japanese/American
phillips thing is new to me.

http://en.wikipedia.org/wiki/Screw
"The Phillips screw drive has slightly rounded corners
in the tool recess, and was designed so the driver will
slip out, or cam out, under high torque to prevent
over-tightening."

I had no idea that the poor operation of phillips screws
in a repair or maintenance situation was /by design/.
Grrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrr!!!!!
That explains A LOT. Mostly a lot of pain and grief.

Thanks.

 

That's a good way to loosen up stuck float valves. Berryman's B-12

I'll try that stuff next time for sure.

I don't think this happened. I would have noticed this right away,
right?

I started it this morning full choke after a weekend of sitting with no
throttle. Worked great. Started right up. It seems to have problems
if I've ridden it that day, so we'll see over lunch how she does. I
think you hit it on the head about too much gas still in the engine.
This would mean I would have to "blow it out" right? Which is why I
had to open it full throttle to start it?

Lots of great info! Thanks! I always like to learn that kind of
intricate stuff. I wish I could tear into this stuff more. I don't
think my plug was drilled. I think that would have been too proactive
for the previous owner. They were lazy or just had no know how. I
don't think they cared enough to take it to a mechanic.

I think I would get myself into trouble messing with the tuning and
mixture of the carb. But, that is great info.

Will do!!

Thanks for all your help! Great feedback everyone. I appreciate all
the interest and advice.

 

Hello again everyone,
I hope the new message gets your attention and I don't have to
repost the problem. I am pretty POed about this bike acting up. I
thought I had it taken care of. Well, I had some trouble starting it
and so I pulled the plug on the hose that drains my airbox and left
about 1/4 of a gallon in the parking lot. Then it started a lot
better. So, Obviously there is a stuck float.
My questions is, Do I try Berryman's first or use the piece of
tubing on the drain nipple thing to find the float that is stuck. If
it is gum, then I suppose they could all use the cleanup. Could it be
that the float parts need replacement?
I think I'll try to get some berrymans to let sit in the floats for
a half hour and then go for a slow ride. FB always posts about it.
Well, If I want to fill the carb with Berrymans, how strong and where
do i put it in at. I thought about using a hose, draining the bowls,
and then filling through the drain nipples. Is this the best way?
Should the petcock solve this problem? I dont' have an on/off
petcock, rather the on/Prime type. So, that requires vacuum to pull
fuel from the tank, would a stuck float pull fuel from a properly
operating fuel valve? How do I trouble shoot that? I would Like to
avoid reworking my carbs if possible, I've never done it and I'd rather
avoid more trouble caused by me being clumsy with things I don't know
how to do. Thanks for your patience with the new guy.

Tim

 

I'll try this.

How do i do this? BikeBandit wants 85 big ones for a new assembly.
Can I buy a kit? Where? I Put in the link for the convenience of
anyone willing to help me.

http://houseofmotorcycles.bikebandi...id~987331~model_dept_name~GSX750FY+KATANA.asp

Thanks!

 

As Mark said, you might also have a leaky automatic petcock/ The rubber
diaphragm might leak or the vacuum operated shutoff valve on the
backside of the petcock might not be seated. The engine vacuum pulls
the valve open and a little spring pushes it closed.

However, if there is a lot of rust and debris in the bottom of your gas
tank, you might have crud holding the automatic shut off valve open.

So, disconnect the fuel hose from the petcock and watch to see if the
petcock keeps dripping gasoline or if a steady stream of gasoline comes
out.

It may be time to remove the gas tank and take off the petcock and
flush out the gas tank with fresh gasoline.

Another way a petcock can leak is when the four-holed rubber grommet
gets a groove worn in
it from operating the selector lever while the grommet is dry. This
happens when an owner leaves the machine set unriddden for months at a
time and then tries to select the RES or PRI position.

The PRI position allows gasoline to flow out of the PRI port in the
petcock to the RUN port, but you can get unwanted fuel flow even when
the PRI position is not selected on the petcock.

I have had occasion to open up the petcock and flip the 4-holed grommet
over, or rotate it to a different position so the groove between holes
didn't line up between the PRI port and the RUN port. Then, when I had
a chance to get to the motorcycle parts store, I would buy a new
grommet.

I think it's quicker just to put the Berryman's in the gas tank and I
make a practice of routinely doing that three or four times a year.

It might just be gum and varnish on the float valves. Or, there might
be crud on the float valve seat. I have seen a piece of crud no bigger
than a fly speck keep the float valve from seating.

If I need to put the berryman's into the carburetor directly, I mix it
50/50 with gasoline and then squirt it down the fuel hose until it
fills all four carbs, Then I let it set for half an hour before I
reconn ect the fuel hose and start the engine. It will run on
Berryman's mixed with gasoline and the mixture will get sucked through
the idle ports and idle jets and clean them out.

 

I have taken off the tank numerous times. To change the plugs, try and
clean the carbs.....I usually set it upright and I don't ever recall
the tank dripping gasoline on the floor or anything. However, one time
I got it back together and could not start it. I just wiggled the
selector lever on the petcock and presto, she ran right away. So, I
don't doubt that something could be up, but it doesn't leak when
disconnected.

PS. I have to look for Berrymans after work. I think my parts store
only carries the aerosal form. I'll try a different store if I have
to.