Need some general info about Suzuki GSX 750

In the case of missiles and suchlike, I sometimes heave a sigh of
relief. Swords into ploughshares and all that.

But I do sometimes look at the pix of Davis-Monthan and sigh
wistfully.....

 

I hate to ask but is it possible or probable that my carbs are so far off?

Removed the rack of carbs
Removed the float bowls
Removed the main jets and lock washers
Removed the rubber plugs by main jets
Washed everything with whole can of spray cleaner
Ran wire through main jets as a couple seemed a little smaller
There is a piece that looks like a rod with a small jet that hangs down
between the floats. I am not sure if it is clear or how to remove it.

The shop manual says with carbs upside down, and bowls and gaskets
removed, the distance from where the metal would contact the gasket to
the upper flat surface on the float (not the round part but where the
round part mates with it) should be 22.4 mm +/- 1.0 mm.

Trouble is I am measuring
#1 17.6 mm
#2 18.8 mm
#3 16.6 mm
#4 17.3 mm

That means that there is 5.8 ]mm to 3.6 mm too MUCH (?) fuel in each carb.
Remember this is engine that only runs on #1 which was also putting gas
into the airbox expansion chamber.

Ian Singer

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The Suzuki manual says "invert the carburetor body holding the float arm
pin so it will not slip off. With the float arm kept free, measure the
height (A) while the float arm is just in contact with the needle valve
by using the calipers." that's what it is doing and the tang on the
float is touching the needle valve but it doesn't have enough weight to
depress it.

I have not removed the carb tops as can't crack the screws loose.

But the carb does not have drain nipples it has screw in bolts and I do
not have screw in nipples to replace with.

I won't adjust anything unless its seriously suggested it is wrong.

Another unrelated question. When looking into the carbs from the choke
side three of them have a hole inside the body on either side. One only
has one hole. Why is that?

Ian Singer

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Not from the factory, but who knows what Joe Shadetree the enthusiatic
mechanic may have done to your carbs?

The main jets would have a flat washer under them, not a lockwasher.
The main jets screw into the
brass jet holder, and it can be pressed out of the carburetor body so
you can clean the air emulsion holes.

The nature of a CV carburetor is that it doesn't allow the engine to
even *begin* to draw very much fuel through the main jets until the
slides lift past the untapered part of the jet needle. The engine is
getting 3/4's of its fuel from the idle jets until the slide has lifted
to about 75% open.

The idle jets would be under those rubber plugs. Did you remove the
idle jets so you could clean the cross-drilled air emulsion holes?
Never try to remove an idle jet unless you have a small radio slot
screwdriver that fits the jet perfectly.

I don't know whether you're decribing the main jet and its holder, or
if you're decribing the brass tube that goes down into a hole in the
float bowl and draws fuel for the idle jets. The idle jets were
concealed under those rubber plugs so they wouldn't "see" a variable
fuel level as the motorcycle traversed road bumps are was leaned side
to side.

The system is due to the EPA's clean air requirements.

That's the same dimension as the BS-34SS carbs on my GS-1100EZ...

Are you sure the floats are installed right side up?

======================

 

Are you looking at the inlet bell mouth? You would typically see a
round hole on the same side as the starting enrichener valve, and that
would be the air inlet for the "choke". The small round hole on the
opposite side would be either an inlet for emulsion air for the needle
jet, or it might be the idle air inlet. But in some carburetors, the
idle air inlet is inside the carburetor body, underneath the diaphragm.

A large oval shaped hole would be the air inlet for atmospheric
pressure to lift the slide as engine vacuum sucks air out of the
diaphragm chamber.

Looking at the other side of the carbs, downstream of the throttle
body, you would see the triangular pattern of the transition jets, the
single idle outlet port that is controlled by the idle mixture screw
and the starting enrichener's outlet, which would be a much larger
hole.

One carburetor of the bank of four (probably #2) would have a similarly
large hole for vacuum to operate the petcock.

While you have the carbs off the engine, are you going to drill out the
EPA plugs and clean out the
idle port?

 

??? Is it possible that some PO installed a mismatched set of mains?

Note that the float heights on #1 and #4 are quite similar, within
0.3mm. I'd expect #4 to run, were it the case that the float height were
the only problem. This does not rule out float height as a problem,
however.

As I understand it, low height means too much fuel in your carbs, and
that is consistent with the #1 carb puking fuel into the airbox.
However, it is _not_ consistent with dry spark plugs in the other three
cylinders.

--
Later,
John



'indiana' is a 'nolnn' and 'hoosier' is a 'solkk'. Indiana doesn't solkk.

 

Maybe when I put back together I will find that I flushed some junk out?

Yes one of the reasons I am confused. Spark on all four plugs but three
plugs are dry. Don't forget coils, CD Ignitor and regulator are all off
of other bikes.

Ian Singer

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My error they were flat washers

How do you press it out of a hole? Remove the top plate which has frozen
screws and slide and everything else up there?

OK just pulled idle jet on #2 and it's plugged solid. Eyes are getting
too old to see that it would even come out, ended up with reading
glasses, magnifying glass and flashlight. Will try and run a wire down
it from stranded 22 gauge wire until I get thickness that fits. After
will pull others. Looking in the shop manual again that jet they call a
pilot jet. They say there is another pilot jet on the left side of the
intake throat when you look into carb from intake side.

Must be the brass tube I am talking about that I can't see in the
manual. It has a hole in the end and at the opposite end (towards top of
carb) there is hole in side. Looks like the hole in end might be plugged
but not sure if it's removeableor how best to unplug.

OK I see what gives now. Manual says remove the gasket. I removed gasket
and measured with carb inverted from the top of the metal flange to the
top flat surface of the float. Yes it's correct way up. Looking again
that's not where to measure, it's supposed to be to the bottom surface
of where the gasket goes, so that adds 3.1 mm, meaning #4 is not 17.3
mm but 22.3 mm (OK so there is also a .1 difference where I can't
measure). That makes a lot more sense and means that one is right.

You ae right again. #2 on exhaust side is for vacuum petcock.

I know I should but where is it? My older bikes used to have two
adjusting screws, one for mixture and one for speed, but this style does
not.

If I get too confused might end up posting pictures on my website so we
are talking about same thing. Diagrams on Bike Bandit are not good enough.

Ian Singer

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Yes, from what I recall, it pushes down toward the float bowl when you
have the diaphragm cover off.
It doesn't take a lot of force. There may or may not be a rubber o-ring
on the jet holder.

Probably the pilot air jet, which meters air to the idle mixture
passages.

Use aerosol carburetor cleaner to spritz it out.

BS34SS carbs had EPA plugs on top of the carbs.

Look for a round aluminum plug on top of each carburetor, forward of
the diaphragm cap.

You can take a small drill and very carefully make a pilot hole in the
EPA plug, then enlarge it so you screw a small sheetmetal screw into
the plug. Then you can pull the screw out with a pair of pliers and the
EPA plug with come with it.

Don't drill your pilot hole too deep, you'll hit the idle mixture
screw. The aluminum plugs are very thin though.

Once the plug is out, screw each screw all the way clockwise until it
bottoms lightly, counting the turns.

Write that number down, it may be unique for each carburetor. Then
remove the idle mixture screws, keeping track of the spring, tiny
washer, and tiny o-ring. If there is no o-ring, it's probably still in
the hole.

Once you have the idle mixture screws out, you can spritz aerosol carb
cleaner through all the holes while blocking off some holes with your
fingers to be sure that you see a strong flow of carb cleaner out of
each set of holes.

Then you can re-install the idle mixture screws, paying careful
attention to the order of assembly. Spring goes on the screw, then
washer, then o-ring.

Screw each idle mixture screw back into the same hole it came out of.
Bottom the screw lightly in the hole, then back it out the same number
of turns you wrote down, and you will be back to the original factory
setting, which is probably too lean for easy starting and quick warm
up.

You can enhance starting and warm up and throttle response by opening
the idle mixture screws 1/4 to 1/2 a turn. If the idle mixture is too
rich, the idle RPM will tend to hang up for a long time when you
"blip" the throttle.

There is a photo article on www.thegsresources.com about cleaning a set
of really grungy carbs. You might learn something useful by looking at
that page.

 

As your conversation with B-12 indicates you have already found: dry
plugs = no gas = plugged up carbs. I'd urge you to pull down the carbs
as far as you can, and clean every part as well as possible. You might
get lucky and _only_ have incredibly plugged-up carbs.

For the tops, if you're not willing/able to use an impact driver on
them, you can try heating the screws (be _extremely_ careful using heat
sources around components that have been in contact with gasoline!). The
differential heating of steel and Aluminum should break loose the
corrosion that's holding it all together, and do so fairly quickly.
Penetrants may or may not work, depending mostly on whether or not you
can get them into the holes.

--
Later,
John



'indiana' is a 'nolnn' and 'hoosier' is a 'solkk'. Indiana doesn't solkk.

 

Turns out they were all plugged except for #1 which I can not remove.
Some of them looked pretty mangled so someone has been in it before. I
either leave #1 or see if its possible to drill out and put a new one
in. Inclined to leave.

Actually it's good and hadn't seen that one before. Suggest the PDF at
http://www.thegsresources.com/files/GS Carb Cleaning Series.pdf as
its much easier and makes thing a lot clearer.

Ian Singer


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Lists the tang? Not on mine. The tang presses against the float needle,
it is not connected to it and does not lift it. As the floats raise they
press against the valve to close it.

Ian Singer

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I've read about a lot of concerns about inadvertently bending the tang
on the float that pushes against the float valve, and I suppose you
could bend the tangs out of adjustment if you set the carburetors float
side down on your work bench with the float bowls removed.

The pressure of gasoline against the float valve is very low, something
like 1/4 of a pound per square inch, and the seat area of the float
valve is far less than 1 square inch, so the float operates against a
very small resistance from fuel flow, it has a lot more bouyancy than
the fuel pressure it's trying to
shut off.

In fact, a carburetor float will sucessfully control several pounds of
fuel pressure from an electric fuel pump.

If the tang was really easily bent under normal operating conditions,
the floats would go out of adjustment frequently, but they just don't.

The float valve itself has a small spring on it that takes up extra
motion of the float, after it has shut the fuel flow off. I'm trying to
imagine the bouyancy of the float lifting it so hard that the tang
bends, but I can't...

 

OK, I looked at the carburetor cleaning photos on
www.thegsresources.com and found out that the brass tube with its fixed
starter jet is the fuel supply for the starting enrichener (so-called
"choke").

The starter jet has to suck fuel out of a well in the front of the
float bowl, so cleaning that tube and the well out at the same time is
important.

 

And as three of them are blocked that would explain three dry plugs.
Finally got through them with WD40 (as it doesn't stink so bad as the
carb cleaner in the house) and their "Special Tool" of a wire from a wire.

Ian Singer



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It's amazing that your engine would even run on one cylinder...

 

After replacing spark plugs, cleaning the inside of the carbs, main and
pilot jets, all except for #1 pilot that will not remove, wiping down
needle valve, not removing air screws, or adjusting floats, or removing
float valves, checking diaphragms, replacing bowl screws and top cover
screws with allen head, it started first time on three cylinders and
fourth kicked in after a bit. Idle was much too high so adjusted nuts on
throttle cable.

Stupid drain plugs were leaking again so had to tighten more.

Are the air screws with the EPA covers the vertical one on the engine
side of throat? If so I have no covers on them and can't see how they
could have them as they sure are not recessed.

Engine sounds a little loose with a bit of slap someplace. Can't tell
where, know it has not been running for at least five years so will see
what it's like when I change oil and filter and put new tires on.

Thanks for help.

Ian Singer



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Maybe the mechanic who drilled the plugs out adjusted them five turns
out? Anything more than three full turns open is usually far too much,
even for a # 35 idle jet.

If you pull the clutch lever in, and some noise goes away, it is a
loose clutch basket.

A metallic clanking sound on the left side of the engine can be a loose
starter clutch.

Also, check the cam chain tensioner to be sure that the plunger isn't
stuck.

 

Thought you were going to say that. On older bikes they were on the side
of the carb and all you needed was a long screwdriver. Looks like to get
to these you have to pull the tank and use a super long one. Probably
before touching them I should run it long enough to check out the plugs,
and if they look OK maybe not mess with them. Also if there was another
1/2" of space back to front the carbs sure would be easier to remove.

As in one of the springs being weak or broken?

It's not a clanking, and it really does sound like a slapping sound and
thought it would be from top or bottom of one of the connecting rods
being worn. Can't isolate where it is but is definitely not cam chain
hitting something and not a scarping sound. Was too late at night when I
had it running to rev it up as sounds very throaty.

Ian Singer

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Most likely just a clutch basket that has enough clearance to rattle a
bit. Many bikes do it and it's not an issue.

--
Later,
John



'indiana' is a 'nolnn' and 'hoosier' is a 'solkk'. Indiana doesn't solkk.