Need some general info about Suzuki GSX 750

OK finally pulled the carbs from my 84 Suzuki GS650GLD. Kind of a pain
and I could not undo the screw on the top of #3 that holds the bracket
for the choke cable so had to disconnect it from handle bar end.

Two obvious things that may have caused problems.
1. Overflow hose on the right side was routed UNDER the clamp for #4
that holds it to the air box, so if there was any gas in it it wasn't
getting out.
2. When I moved the starter valve shaft lever for the choke I was sure
that the butterflies for #1 and #2 were not closing down. But then
tried it a couple of times and that lever is the bar that goes across
the front of all the carbs, and does not control the choke at all, so I
am not sure what was happening. It was also the lever that was frozen
into position a month ago and I freed up with WD40. When I move the
correct piece they are all moving now.

The slides all seem to be free going up, but a couple stick a bit going
down when they are close to the bottom.

I will try a liquid carb cleaner, without doing any disassembly, to see
if that will help, and if so will not have to change gaskets or rebalance.

Ian Singer





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Suggestions please:

I pulled the rack of carbs. Did not want to disassemble. That will be
last resort as would have to buy gasket sets etc.

Sprayed with whole can of carb throat cleaner that contains xylene and
methanol. Slides do not stick, ran through all ports, pulled drain plugs
and sprayed inside of bowls. Everything seems OK without doing a
disassembly. (Can't buy B-12 here and a can of Wynns in gas tank did not
seem to help before).

Changed petcock for used one, gas and vacuum lines replaced for the
right size.

Changed all four plugs for new NGK DR8EA. I have spark on all 4 plugs.
Compression not checked as no gage.

This is on bike that has been sitting for many many years and coils,
regulator and CDI units are all used from ebay. Coils have spacers on
bolts that keep them away from frame, and they are aluminium if that
makes any difference for grounding.

Giving it a little throttle I can get it to run, but only on cylinder
#1. All others are cold. Coils are wired to #1 and #4, #2 and #3 which
is correct.

Sparks appear weak but all messages here say that is fine.

Unrelated, maybe, my gas gage is not working even when the wires are
shorted out as the manual says to test.

I have not pulled the drain plugs on carbs to check for gas in float
bowls after putting carbs back on.

I have not tried switching coils to other cylinders to see if firing
cylinder moves.


Ideas?????

Ian Singer


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Well, there is still the "thumb test". With the spark plug out of its
hole, crank the engine and see if you have any compression at each
cylinder. It's possible that you have some valves that aren't seating
correcting because they've been for so long while the motorbike wasn't
running

You might try squirting your carb cleaner down the fuel line into the
carbs to free the float valves, and hand choking the carbs by literally
placing the palm of your hand over the inlet while the engine is
running will sometimes suck gasoline up into the idle circuits.

 

From what you report, it seems likely that you've got a combination of
problems. If you swap coils and the hot cylinder moves, then you've got
a pretty good idea that one coil is bad. Replace that before doing
anything drastic. If the hot cylinder doesn't move, then I think it's
time to dive into the carbs.

You might try getting an in-carb cleaner, such as the Yamaha or Seafoam
products. They get mentioned here from time to time, and people seem to
like them. However, most everyone I've ever heard from says that they
don't do the job on really nasty stuff. FWIW, I've never cleaned a carb
out. When I had carbs that needed it, I was too young and dumb, and now
my carbs are clean.

HTH!

--
Later,
John



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

 

That sounds do-able. Will have to tie the clutch lever in to bypass the
safety switch and hope my thumb is long enough to reach the hole and the
same time I am pressing the starter button with the other hand.

When the carbs were off and upside down I think I sprayed enough in the
enough in the drain holes to clean the bowls. Also in the hole on either
side of the carb intake and the one on the top of the intake. If
anything I may have sprayed too much in around the slide so it filled
the area above it but am sure it would have all drained out.

Can't do that without taking the front part of the air box off. It might
come off if the carbs are pulled again but everything is kind of tight.

I can also try switching coil to see if good cylinder follows it, but as
each coil drives two cylinders would be strange if one was half dead.


Will advise. Thanks.


Ian Singer



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Agreed but as each coil is for two cylinders would be unusual for one to
be half dead. Will swap though and see. Will try for compression check
too. Also would be strange for a CDI to be partially dead.

The automotive carb throat cleaner seemed to be pretty good and you
could see that when it was sprayed in the xylene and methanol were
dissolving everything. Also am sure the floats are moving as before
there was problem with gas coming out the overflows, and that's not
happening now.

Really hate to take carbs apart as without changing floats cheapest kits
on ebay come to $US 40 plus shipping. Then would have to re-balance etc.
Also I know one of the screws that holds a top cover on is frozen and
will probably need an impact driver to remove.

Could try more starter ether but before the cleaning it was backfiring
and flaming out the air cleaner!

Ian Singer



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Promise me that you won't tell Ted Mittelstadt what I am about to say.
;-)

I have taken the liberty of bypassing the clutch switches on three of
my four motorcycles, and will bypass the remaining switch when it stops
working reliably.

It's easy enough to do, I just cut the wires off the switch, strip the
ends, and solder them together and insulate the solder splice with heat
shrink tubing.

I also bypass or disconnect so-called sidestand "safety" interlock
switches at the first sign of problems.

You might have to bite the bullet and disassemble the carburetors for a
thorough cleaning as I have described a bazillion times in this NG.

 

People talk about installing rebuild kits in motorcycle carburetors
just like they talk about installing rebuild kits in high mileage
automobile engines.

I don't see why they think a motorcycle is going to need a rebuild kit.


Neglected motorcycles usually don't have a lot of miles on them when
they change hands, the real problem is that the gasoline has evaporated
in them and plugged up all the small passages and jets.

I've never needed a rebuild kit, and I put more miles on my motorcycles
than most riders.

But I never need any parts at all when I clean out a carb. The
professionals, like Mark Salvisberg at Factory Pro, do see a lot of
strange carburetor problems, like worn jet needles from excess
vibration and worn out needle jets from the needle hitting it because
the carburetor is installed on an angle in some machines.

But, none of my carburetors ever needs any brass parts or floats, just
careful disassembly, cleaning, and reassembly.

If you don't separate all four carbs, chances are you don't need to
synchronize the carbs. Carburetor $ynchronizing is a big money maker
for the mechanic$ at the $tealer$hip$. They prey upon the ignorant
newbie rider who wants to maintain his machine immaculately.

The actual reason that his machine runs rough is because the idle jets
and idle passages get plugged up while the motorcycle is stored during
the winter, and, if the rider knows enough to use a carburetor cleaner
in the gasoline, the gum and varnish problem is solved and the carbs
never need to be re-$ynchonized by a predatory mechanic.

I have never paid a mechanic to $ynchronize any of my carbs and I have
owned multicarburetor vehicles for over 40 years. A "professional"
mechanic once saw me tinkering with my old Jaguar in front of the house
and he told me I should bring it into his shop so he could "fix" it.

I told him that it was Christmas and I was short of money, and besides,
the car was going to be in another town after the holidays. So he
volunteered to "help" me. He told me that he was eager to work on any
Jaguar.

He tried to adjust my carbs for an hour, and couldn't do it. It was a
good thing I didn't *pay* him to
fiddle around with the carbs...

I bought an impact driver, about 35 years ago. Used it a few times, and
sold it at a swap meet and never bought another one. Nowadays, I just
use an old Phillips screwdriver that fits the screw head and I whack
the screwdriver handle with a hammer, while turning the screwdriver.

It seems that any time an engine isn't running, some of the valves are
always going to be open, and the springs will be compressed.

One guy claimed that the valve springs on Suzukis were so weak, the
engine had to run a little while for the valve springs to "remember"
how long they should be. He said that his GS750 engine would always
spit back through the carbs when it was cold.

Backfiring through the carbs can point eiher to plugged up carburetors
or to intake valves that don't seal properly.

With a dual-fire ignition system, it's hard to say if backfiring
through the carburetor indicates an intake valve that isn't seating
properly.

The backfiring could be caused by the waste spark in the cylinder
that's on the exhaust stroke igniting accumulated fuel air mixture that
didn't light off on the compression stroke for that cylinder.

 

That's why I think it's a combination of problems. That is, that you've
got one good cylinder, and _something else_ is keeping the second
cylinder on that (good) coil from firing. Unfortunately, there's not
really any way of testing that without getting another coil.

As for the compression test, your reply to B-12 indicates that you want
to turn the engine over with the starter. I'd turn the engine over by
hand, instead. There should be a timing cover on your bike, and you
should be able to turn the engine over with a large socket on the nut on
the timing plate. At least, I think the GSs did it that way. I haven't
owned one in a while.

Turning the engine over by hand puts your arms closer together. You also
have finer control over engine speed and stop-point.

You'll need to rebalance anyway, if the carbs were anything like in
balance before. All sorts of stuff will shift in the cleaning process,
and possibly throw things out of synch.

Yup. A hand-held impact driver will almost always do the job. Then I'd
go to a hardware store and get socket-head machine screws (i.e. the ones
that take a hex-key) to replace all that phillips hardware. It's cheap
insurance against chewing something up the next time.

Get video if you do.

;-)

--
Later,
John



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

 

A friend suggested that if the cabs were removed, and inverted, it could
bend the tangs on the floats. Is that as preposterous as it sounds to me?


I switched the coil leads and the good cylinder did not move.

Then looked at the coils again and I had the + and - leads on one
switched. Reversed it and it started and ran better but still on #1
cylinder only.

Tried the thumb test and all cylinders have compression.

Attempted to pull carbs again as that is only way to remove air box and
was going to try manually choking a bad cylinder or spraying more
cleaner in. Turns out air box had a lot of gas in it and it looked like
it was coming from #1 carb as that was leaking out the inlet throat.
Strange as that's only one that's firing and that plug looks way too
rich. Non firing plugs are dry so that mean no gas to fire.

Inside the air box that attaches to carbs, not sure if it's air box or
expansion chamber, but the one the other box with air cleaner attaches
to, I see that each rubber piece that attached to carb has a brass
strip that looks like it might be to add stiffness where the rubber boot
attaches to box. Any ways three of them were totally in wrong place and
at angles blocking air path. Not sure if that is way they were, or if
they got that way moving carbs. Also not sure they will stay in
position when carbs go back on.

Reason I was thinking of carb kits was I figured removing the float
bowls would destroy the gasket.

On impact driver....used to have one for my Honda 160 back in the
1970's. Could never get it to work right and ended up changing all the
case bolds for allen head.

Still stumped. Guess keep my eyes open for another set of coils and
possibly carbs.


Ian Singer

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Sounds like both coils work, then. At least provisionally, I'd call them
good and concentrate on the fuel/air sides of the triangle. I predict
that it's going to come down to pulling the carbs and tearing them down.
(sorry)

[snip]

Sounds like that might be part of the problem. You might already have
been given the advise, but there are ways of making it easier to
remove/install your airbox and carb boots. Gentle heat applied with a
hair dryer or heat gun (be _very_ careful if you use a heat gun!)
softens boots. Some silicone spray lube makes it easier to get them on
and off, and seems to keep the rubber from hardening up if you spray
them periodically.

Sometimes it does, sometimes it doesn't. It doesn't hurt to have gaskets
on hand, for just this reason. However, there's no absolute need to buy
kits just for the gaskets. If you're reasonably patient and good with a
razor-knife, you can cut your own from bulk gasket felt. A big roll is
cheap (probably less than $5 US) and will make _lots_ of gaskets.

Part of the issue is that Japanese philips/cross-head screws have a
different profile than US ones. So, US screwdrivers and bits don't quite
fit. You can buy Japanese-profile drivers from places, but I'd just go
with socket-head screws instead. It's just a more positive system and
works better.

Good luck with it!

--
Later,
John



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

 

I bought one..., oh, must be nearly 30 years ago. Still have it. Still
use it. Any screw that I've not undone before, out comes the driver as
SOP.

I bought a good one - I remember it was pricey back then. But I've had
30 years' use out of it. Buying quality tools is always cheaper in the
long run.

 

About 25 min east of Toronto Canada.

Ian Singer

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Was looking in Google and they mention problems of the engine dying can
be caused by a bad regulator and that can be caused by bad headlight.
As my headlight is disconnected wonder if that could be part of my
problem of only running on one cylinder?

Ian Singer


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Yes, that is ridiculous. If you removed the float bowls and set the
carbs down rightside up so they rested on the floats, then *that* could
bend the tangs.

But, so what? Any home mechanic that can read a Clymer's manual can
reset the float height, using a plastic caliper.

I've never seen anyhting like that before. Do the brass strips look
home made or like they came from the factory?

If you can't tell whether the parts you have are any good, how will you
be able to tell if the replacement parts are any good?

I used to buy a lot of unnecessary parts when I first got into
do-it-yourself mechanics. I didn't know how to tell whether anything
was any good or not.

But I think your main problem is plugged up idle circuits and the only
way you're going to clean them out is to do a thorough cleaning of the
jets and idle passages.

 

They show at http://houseofmotorcycles.bikebandit.com/partsbandit/
oem_schematic_view~schem_dept_id~707627~section_dept_id~1~section_dept_name~
OEM+%28Stock%29+Parts~dept_type_id~2~model_dept_year~1983~model_dept_mfr~Suzuki~
model_dept_id~703462~model_dept_name~GS650MD.asp

(All one line)
as part number 4 Ring Outlet Tub 484164-001. Yes I know that's for a
GS650MD and I have GS650GLD but that's the air box I have. As far as I
can tell they go all the way in and basically line up at the same level
as intersection of the boot and the box.

Well I had checked the resistance of the coils and they were OK.

You mean like my spare engine, drive shaft etc. that were so cheap it
would have been a crime to turn them down.

Me too especially as the gas was leaking into the air box it suggests
the float is not seating on that carb and as the other three plugs were
dry those carbs must be plugged. Oh well will have to take them apart.

Ian Singer


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Only on systems that use the lighting to balance the charging circuit. I
don't believe that your GS is such a machine (though again, it's been a
while since I've owned one).

--
Later,
John



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

 

Technically, the "air box" you describe is called a "Helmholtz
Resonator".

It resonates at a frequency that opposes the adverse pressure waves
returning from the exhaust system at certain RPM during camshaft
overlap. It helps to smooth out the torque curve between 5000 and 7000
RPM.

I hereby nickname the mysterious parts "Klutz Rings" and assign them
the task of preventing a certain shade tree mechanic named "Hermann
Klutz" from overtightening the inlet hose clamps and breaking the
spigots on the Helmholtz Resonator, which is made of ABS plastic.

I understand the feeling, intimately. All those mass-produced
motorcycle parts, languishing unwanted in someone's garage are as
tempting as a litter of 4-week old kittens. You just want to rescue
them so badly, but you can't...

 

You are going to get hell from some unnamed people for the extent of
your verbosity!

Actually that's not tue. The resonator box may be ABS but I think it's
actually a little softer. The spigots are rubber and go into holes in
the box and the rings go inside the rubber. Not actually sure if the
carbs insert far enough in to contact the rings. What I also did not
realize was that the spigots rotate and because they are angled it
changes the spacing between them.

But a bunch of parts and a complete engine for $10 was absolutely non
refuseable! Cutting up the frame though, as there was no registerable
ownership, seemed like total desecration and blasphemy.

Ian Singer



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My critics have the same options as anyone else who peruses this NG.
They have to choice to read, or not to read, to decide whether my
offerings are unvalidated opinion, or the pure gold of experiential
wisdom.

It's their choice. In the meantime, I practice equanimity, evolving
towards perfection... ;-)

Yeah, I know. I worked at companies where classic airplanes and
missiles and spacecraft were sitting around, waiting to be scrapped. It
always made me sad to see vehicles which were the product of so much
aspiration and so much cooperation and teamwork go to the wrecker.