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Answer
Mike, Always start at the beginning when troubleshooting a cylinder miss issue.
Compression... How much? If low, always check valve clearances, then recheck.
Standard readings will be around 150-175 psi.
After that, I always suggest that the spark advancer be examined for proper
advance/retard function. Clean and lubricate. Be sure to mark the point cam, if
you slide it off the advancer base, as you have a 50-50 chance of intalling it
backwards and fouling up the ignition timing.
Once that is checked, clean the point faces thoroughly, then set the gaps to
.012-.014" at the highest spot on the point cam. Afterwards, check the ignition
timing to assure that the points just open at the LF and F mark alignments.
Put in FRESH spark plugs (once they are fouled, it is hard to get a reliable
spark again). Actually, before you put them in, check for a good clean spark
with plugs lying against the head. While you are cranking the engine over, check
the points for excessive arcing. If one side has persistent arcing across the
point faces, then check the condenser connections, up under the fuel tank. If
they are clean and tight, then you probably have a failed condenser set. They
come as a unit of two, so both have to be replaced. They are pricey from Honda,
so check Ebay or even try one from a small Japanese Car from that era, spliced
into the circuit.
Check the spark plug caps for resistance readings. Should be around 5k ohms and
be tightly installed on the plug wire end. So much for the electrics and basic
tuning.
CB350 carbs have rubber diaphragms for the slide that often tear or get pinholes
in them. Check this first! If they are damaged, they will never work properly.
Check cable syncronization and idle mixture screw settings. Set both side the
same to start. Try about 1 turn out on the mixture screws first.
The carbs have some numbers/letters stamped on the bodies, indicating a certain
calibration set and they changed them quite a bit during the production run.
Find out what the stampings are, so I can provide the correct settings.
Other carb issues are float levels incorrect, the floats have pinholes in them,
causing them to sink, numerous O-rings inside can fail and jets/emulsion tubes
and air passages can get blocked with varnish and dirt. Everything has to be
clean and to original specs.
Petcocks can get blocked, sometimes, allowing more fuel to one carb than the
other. Be sure that the gas cap vent holes are clear, too.
If you let these bikes sit with old gas in the carbs, it will evaporate quickly,
leaving deposits that can upset the calibration of the units.
Always start with a fully charged battery and be sure that the charging system
is fully functional.
1997 Suzuki GSXR1100W. I bought this bike with a
miss in it last summer. The seller told me that it had set on his showroom for
almost a year and that I should run some carb cleaner through it via pouring it
in the gas tank for a couple of tanks fulls. If that didn't clear it up then he
would clean the carbs for me. That didn't work so I took it to him and he "said"
he cleaned the carbs however the problem returned 1 day later.
So from there I continued pouring octane booster and carb cleaner in the tank
until this past spring. I changed the exhaust with a D&D full exhaust. Friends
of mine said that it wasn't breathing and that should help it. It didn't. I took
it to the local Suzuki dealer and they sync'ed the carbs and changed the plugs
but they couldn't get the miss out either and wanted to take the carbs off for
cleaning. I didn't let them do it and picked the bike back up.
Then I bought a K&N stage 1 jet kit for the bike and had another mechanic put it
in. He did and I got the carbs back on the bike. It fired right up and sounded
better at idle and it had very increased throttle response but when I took it
out it would start running (on what sounded like 2 cylinders) at 4000 rpm on up.
At idle it sounded better but still sounded as if it were still missing but not
as much. Actually, the bike has never ran right the whole time I've had it so I
have no idea what it's supposed to sound like when it is running right. But
after 4000 rpm it sounds horrible and is herky-jerky to drive. There also seems
to be a lot more vibration in the handle bars (that could be something else). It
drinks a lot more gas since jet kit was installed. A tank now goes 1/2 the
distance it used to. I'm not sure if that's normal or not.
I bought a mercury carb synchronizer and plugged them up to the ports on top of
the carbs and fired it up. I bought this because the guy who put the kit in
didn't get them back in sync. So anyway, I plugged this thing up and now I'm not
sure where the adjusting screws are that I'm supposed to be turning. I need to
know what to turn and where the mercury should be up to on this tool. It starts
at the bottom with the number 2 and by 2's it goes up to 54. But the mercury
goes instantly to 18 on a couple of cylinders when started and 22 on 1 and 16 on
the other. These numbers also fluctuate while it's running because of the
missing. The 22 will go up to 26 and the 16 will go as low as 12. The directions
said to get the levels as close as possible...I don't know how to sync these
carbs..at all! The other thing is the air filter isn't that bad but I was
thinking about replacing the whole box with individual filters. I'm not sure if
this will help or hurt. It would seem this bike needs less fuel and more air but
what do I know...that's why I'm here.
I'm sure this won't be the first and last time you hear from me.
Thanks in advance for your time.
Answer
Hi Randy,
Great description. That's a treat for a tech. Thanks!
I'll try and send carburetor cleaning, tuning, and synchronizing files to your
Juno email account. Some email hosts cannot handle my files do to their size.
We'll get them to you one way or another.
When working with carbs, its important to make one change at a time to know what
effect each change makes. Otherwise you end re-doing everything and staring
over, repeatedly.
First thing to do is get a cylinder compression reading to me. Next, describe
the appearance of the spark plugs with respect to the cylinder they reside
within. Cylinders are numbered 1-2-3-4 from left, to right. You may need to
perform a "plug-chop" before reading the plugs.
Keep in mind that we tune carbs by first throttle opening position: 1/4, 1/2,
mid-range, wide full open (WFO). RPM's come second for fine tuning carbs
air-fuel mixture.
Check your email for my files. Review the files before you begin working on the
MC. Review them again as you work. Work patiently and methodically. Trust you
can do the work yourself with a little help.
Synchronizing: It's important for valve clearances and cylinder compression to
be with in specs. Carbs alone will not work properly if compression is not up to
par.
Connect hoses, plug vacuum hos from carbs to petcock (if any), open vent on sych
tool, keep fan in front of engine, deaccelerate or close throttle slowly to
avoid getting heavy metal Mercury into engine (Mercury fumes are very toxic).
With engine idling, adjust Mercury levels across tubes. They can be in the
ranges of 20's and 30's and within two lines of each other, but we like to get
them as level as posible. Adust the 1 & 2 carbs together, and the 3 & 4 carbs
together, and then adjust 1-2 & 3-4 banks together. Adjusting may change idle.
Leave it until those two carbs are level, then adjust idle down or up to specs.
Repeat same until done. See files for detailes on synchronizing.
Respectfully,
Mark Shively
Dayton, Ohio
mshively1@woh.rr.com
What if there's a misfire at, say 1/2 throttle,
but only under load ? Carburetion can cause a miss that looks, acts, and feels
exactly like an ignition miss. How do you tell the difference ? Easy, Hook up a
timing light. Use one of the types that does not have to be hooked to a battery
for power, if possible. A lot of the old style lights were like this. Tape it to
your handlebars and go for a ride. Look at the light. If the light looks bright
and steady when the misfire occurs, then the problem is in carburetion. If it
goes out when the misfire occurs, then the problem is with the ignition. There
are all kinds of ways of doing this and you can use different tools, like plug
caps with lights on them. The big thing is being able to see when the spark
occurs... or doesn't occur.
Could be "everything" far as I can see:
Norton Commando? '7x ... - Guess so. Does it
misfire when idling (too)? Also I am sure you are familiar with the
choke/airslide function of the Commando... (pulling/lifting choke/airslide to
let the air in for them Amals(?) to breath).
Most often it is a trivial reason
- loose wiring
- bad / rotten plugs
(once I had one of the Boyer cable shoes bent
right into the cover - fired once in a while...)
Most common misfire reasons(under load):
I. Electric disturbancies
II. Bad valve operation
III. Carburation (make it idle! Pilot level)
In this priority. A timing lamp is necessary in
concidering if regular spark (if firing uneven, it will show on the grade scale
- flashing).
I would begin with plug condition - is it (the
left one if dead sure left is the culprit)
1. oily black? Maybe valve fault, blown head
gasket
2. dry but soothed? Maybe airslides down (choking)
3. wet of unburnt gas but not that oily? Maybe
lack of spark/ignition fault/short circuiting/bad earth
4. dark brown (eg. perfect)? Then its no faulting.
Coil is a very robust device - works or works not.
Elect' (tronic) eg. Boyer Bransden(?):
- If battery voltage below 9V ignition could be
suffering (but most often compensates by the charging)
- If charging too bad (cables loose on battery
f.ex), ignition could be suffering.
Exotic reasons:
1. Cams worn down (valve gear malfunction)
2. Blown head gasket (different symptoms, often
not that obvious except for killing plugs)
-
Cracked cyl and other unspoken reasons
We are all assuming this bike was ridden recently
by you, that you have personally witnessed this bike run, that the high-test
fuel in the tank is less than 4 weeks old, that the spark plugs are new, and
that the plug wires have been replaced in the last 5 years with METAL core
wires.
Good. Then...
Turn your headlamp ON for 2 minutes. Then after 2
minutes with the lamp still ON, measure the battery voltage with a good
voltmeter. If your battery voltage is not AT LEAST 12.0V then you need a new
battery. Period.
Low voltage, especially right at 12.1V will make a
Boyer misfire so that the engine sputters. It sounds so much like a carb problem
that most people jump right into the carbs, but it's the Boyer misfiring for
lack of operating voltage.
Highly suggest you read my articles on the subject
at the GABMA web page.... http://gabma.no-ip.org/
please help my gsxr runs ok on tick over and runs
ok for about 1/2 mile then starts misfiring and looses power and then will not
tickoveri also get some white smoke out of exhaust which i am being told is
electrical any suggestions thanks
Good afternoon Gary,
Check the choke cable isn't sticking first. The
coils could be breaking down when they get hot. Remove the plugs to check the
condition to acsertain whether it is running rich or lean.
If one or more cylinders are dropping at low rev's,
consider cleaning, synchronizing, and tuning the carbs.
Learn to read the appearance of the spark plugs. Plugs may indicate problems
with the A/F mix and ignition/combustion burning problems. "www.ngk.com" Click
the "Plug 4-1-1" link.
Carbon-fouled- Build-up of carbon deposits on
engine parts or spark plug electrodes. Fouled plugs may misfire, causing a loss
of power and wasting fuel.
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