1 out of 4 cylinders dead

Warning: I haven't taken anything apart yet or checked plugs or anything
that requires removing bodywork. I have to go to work in a minute and won't
be able to get into the bike just yet.

Bike ran fine for 2 months. Was left unridden for a week for Christmas
break. Started slowly yesterday when I got back and ran just fine for the
first trip to work. On the ride back home I noticed it was low on power and
it sounded like a v-twin. Got back home (~1mi trip) and pressed up a wet
towel to the pipes. Water evaporated quick on 1, 2, 4, and the third one
didn't evaporate. So dead cylinder, right?

Before getting into the bike and checking the plugs (condition unknown, I
bought it used), is there anything one can think of that would cause this?
It ran fine on its first trip out after the week of no use. Now, it starts
up quick and fine but the third cylinder doesn't fire all the time. It
sometimes does fire every couple of seconds, with a corresponding rise in
RPMs. I jiggled the cable or whatever that goes to the plug in case it got
loose but it didn't make a difference.

So do I need to get the bike apart to check/replace the plugs and spark? Is
there an ignition coil for each cylinder? Could one be bad?

 

It would help to know what bike and model you are talking about....but
what you can do is check to see if you have spark to the third cylinder....
you probably don't since your water testing didn't meet your needs.....in
this case, i would check or replace the wire for this cylinder. I had a
similar problem, but was able to reconnect the wiring to the plug ends so I
had spark...if this isn't the case, let us know so that we can direct you
elsewhere..

Fwed

 

With the very best will in the world, if you're really this unsure of
fault diagnosis, do you really think that giving advice to others is a
good idea?

 

Assuming the bike is a transverse four, then the coils and ignition
systems fire cylinders 1&4 and 2&3.

A single cylinder failing on its own is therefore *not* coil or ignition
(points or CDI) failure.

It could be a single carb acting up - blocked, jammed, whatever. But
this is unlikely.

Start with the basics.

Change the plug on the offending cylinder. If no joy, swap the plug cap
and see if the fault transfers to another cylinder. If it does, then you
have a plug cap problem. If not, then it could be HT lead, but my money
is on something simple like the plug or the cap.

 

Not at all.... in fact if I was unsure, I would not even offer advise...
in fact it looks like you are giving the same advise I am......something
about taking a look at the plug cap on the cylinder that isnt firing....
I am not next to the bike, so I don't see what he sees...only what he is
reporting, which leads me to my diagnosis.... if the bike wree in front of
me, rest assured, I would know what to do, and if I didn't, I would post any
suggestions here.....
Seems like you are picking on me (again)... did I say something to
offend you??
Also seems to me that this persons diagnosis is quite different than what I
would do, and many other people too...... I mean really... have you ever
taken a wet towel to each cylinder to see if it would dry?? At least I have
tools... lol.....
I was merely stating that if my remedy didn't help, (which I am pretty
positive it would) to let us know. There is always that chance it might
not.... as I am not expert, but am willing to share my knowledge...

Fwed

 

Yes!!! This is what I want to hear. I think.

I think so, too.

Is the HT lead the long thing that plugs onto the spark plug? It looks like
(after googling) the spark plug cap is the part that is external and plugs
onto the HT lead. Basically, I'm not really down on terminology.

The bike: 93 CBR600

But here's more detail: This morning I started the bike cold, and it ran on
three cylinders for about a minute while I tried to push the wire leading to
the dead cylinder around, with no result. I was frustrated about riding the
pedal-bike to work and decided to ride the moto anyways. There was a
10-minute gap from starting it cold and when I restarted it to go to work.
When I did restart it, it started up and operated on all four. It behaved
well all the way to work (1 mi).

After work (3 hrs) I started it again and it sounded like it was on 3 again.
But as I rode about .5 mi, it seemed to work itself out and sounded like 4
cyls again. Maybe during warm-up a contact expanded, or the plug gap
narrowed, or something? I'd love to leave things alone because as we all
know, if it ain't broke, don't fix it. At the bicycle shop I work at, I try
to abide by this because a 30-minute repair can easily become a 2-hour
repair.

 

FYI, 93 CBR600. I was trying to wiggle around the external wires at the
tops of the cylinders right after I started it and running, and it didn't
make a difference. It still occasionally popped when the dead cylinder did
fire, but only very sporadically.

Read a couple posts down for some new details... it seems that it is working
okay when warm.

 

It may run after it warms up, but thre is still a problem that needs to
be tracked down...still begs the question.... Are you getting spark to the
cylinder even when its cold? Have you swapped wires to see if the problem
follows? Checked the wire by the coil? Could possibly on that end....

Fwed

 

On a bike that age, especially one that you've only recent purchased, it
wouldn't be a bad idea to take out all of the plugs and compare them. Are
they all the same or did a previous owner stuff an oddball plug in one of
the holes? Do the electrode all look the same color and are they all
properly gapped (see your repair manual for the correct gap). It is
possible that there is gunk in one carb but not the rest, but not likely.
If there is a drain on the carb, empty the bowl and see if any sludge or
small chunks come out. It also wouldn't hurt (maybe would help either) to
put some sea foam or something in the tank and give it a good 50 mile run
when it's hitting on four.

Good luck!

 

The HT lead runs from the ignition coil to the spark plug. As I
understand it, HT is short for "high tension." On many motorcycles, the
cap screws or spikes onto the HT lead (i.e. they are separate items
unlike many automotive applications where the whole assembly is molded
together). Some motorcycles have wires molded into their coils (making
HT-wire problems expensive to fix, but also making poor connections at
the coil less likely), some don't.

Running on 3 cylinders counts as "broke." I'm with the folks that say
start by swapping the caps on the relevant cylinder pair, and then
inspecting the plugs if the trouble doesn't move with the caps.

Here's some sites (30 sec. in Google) with pictures of spark-plugs for
comparison:
http://www.centuryperformance.com/spark2.asp
http://www.verrill.com/moto/sellingguide/sparkplugs/plugcolorchart.htm

While the plugs are out, definitely compare them to Honda's
recommendation for brand and model, particularly heat-range (someone
else here noted this earlier), and replace them if they don't match the
spec. Also definitely check that the spark-plug gap is correct. The
centuryperformance.com link has a discussion (on the previous page) of
various aspects of the ignition system. It's more technical than you're
looking for, and deals with issues that you don't face (or do you have a
nitrous system installed?), but it's there if you want to look it over.
Reading the portion on heat ranges might be helpful, but since you wish
to retain a completely-stock system, it's not critical.

At the same time as you inspect the plugs, you should inspect the caps
and the entire wire run back to the coils. You're looking for
poor-condition insulation (cracks?, tears?), loose connections at either
end, cracked caps, obvious differences in condition between wires.

--
Later,
John



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

 

I would suspect that the idle mixture passages were blocked in that
cylinder's carburetor. If the engine starts and runs on all four
cylinders when you apply the choke, and then starts running on three
cylinders when you move the choke lever to the off position, it's
almost certainly lean idle mixture on that cylinder.

There is a smaller possibility that the spark plug just needs cleaning.
An engine with a lean mixture needs a clean, properly-gapped spark plug
to fire the weak mixture.

 

I would suspect that the idle mixture passages were blocked in that
cylinder's carburetor. If the engine starts and runs on all four
cylinders when you apply the choke, and then starts running on three
cylinders when you move the choke lever to the off position, it's
almost certainly lean idle mixture on that cylinder.

There is a smaller possibility that the spark plug just needs cleaning.
An engine with a lean mixture needs a clean, properly-gapped spark plug
to fire the weak mixture.

 

<snip>

I have taken wet rags to suspect dead exhaust pipes many times. This is
just a sensible precaution in case it *is* live after all. And therefore
hot.

As for fault diagnosis, a few points: every in-line four cylinder bike
that I've ever come across has the firing pattern I described, so your
asking for the bike and model is virtually superfluous. It *could* have
been a V4, I suppose, but the odds were against it.

Secondly, many, if not most Japanese bikes have their HT leads sealed
into the coils, so swapping the "wires" about is not possible.

I merely pointed at the most obvious cause - a duff plug and/or plug
cap. My money's still on that, but I'm happy to be proven wrong, of
course.

 

The lead is the thick electrical wire that goes to the plug. The plug
cap is the plastic doofah that clips onto the plug. John Johnson's
description of attachment is correct.

Just try a new plug in the offending cylinder. If you don't have a
spare, swap two plugs over (clean both while they're out!). See if the
fault transfers. If it does, it's the plug. If it doesn't, swap the plug
caps over. if the fault transfers, it's the cap. If it doesn't, then the
problem really does probably lie with the carb, though it *could* be a
dodgy plug lead.

 

The wet rag trick just plain sounds like a bad idea. There are lots of
other ways to check to see if the cylinder it hot....but i suppose the wet
rag is another way.... (just one I wouldn't use)...
Ok.... I may have been wrong or asked a superfluous question, but in the
past I have been bashed for not including the year and model of bike I
needed help with.... its just sounds like a good idea.
I was able to swap out the leads from the coils on my jap bike. All of
them can be removed (on my bike anyway). What made things harder for me
though was the wire wasn't always "seated" properly, therefore giving me
intermittent problems until I just ended up cutting them a little shorter
and redoing each wire just because of the age of the wire. Thats also
another reason I was trying to get the year and model of the bike....so I
guess it is possible after all.
We both pointed out the obvious case here.... just I felt that you were
belitting me for even suggesting it. I realize you probably know more about
bikes than me... I am no mechanic, but I owned and worked on many bikes in
the past. I don't know alot about them, but I do know alot and when I tried
to share that, you picked on me....so here I am defending my actions, which
is really unnecesary because we are here to help people right?
Now, come to me with a problem with your pinball machine....

Fwed

 

Using a wet rag is a good way. Trust me.

Yes, that's true.

You're right. I apologise. Trouble is, there are *so* many people on
this ng who post the most ridiculous nonsense. I tend to get tired of
it.

Now you're talking. I *love* pinball, but it's not something that's ever
been wildly popular in the UK. You never see them in pubs or bars,
whereas in France it's rare to see a bar that doesn't have a pin table.

I remember playing in a university bar championship, on an old Kiss
table. I didn't win, but I didn't disgrace myself either.

 

I see alot of rediculous postings too....nostly on the pinball group
though..... I just tend to ignore them.....one guy decided to fix his
problem by taking apart the coil and lubing it... ugh... thats a definite no
no.... but i gues its people like him that keep people like me working on
games like his.. lol....
Although many of the game made their way to belgium, or germany, etc.
there are few in the UK..... In fact, they have really become scarce
everywhere since Williams decided to give up pinball and concentrate on the
countertops and shuffle alleys.....There is only one manufacturer left....
Stern.. and the titles they produce aren't the greatest or like they used to
be, but if we want to keep pinball alive (its been dieing a slow death
actually since the inception of video games), we really do need to support
them, no matter what we think....
Did you know that a Kiss pinball goes for a hefty price right now...not
sure why, but seems like a supply and demand issue.... some games are worth
4 times what they sold for originally. They seem like a good investment, but
not these days... if you own many Gottlieb wedgeheads (50's and 60's
especially) you are doing good....
So anyway.. I can write a novel here about pinball....Ever work on a
Vincent??

Fwed

 

That surprises me. I remember it as one of my all-time favourite tables.

I think one reason why pin tables are dying out is thay they're
expensive to make and the games can last a long time if an expert is
playing - hence the return isn't as good as it is with video games.

In the UK, we've seen bar billards tables dying out in favour of pool
for much the same reason, But bar billiards is a lovely game.

No....

 

I remember playing backin high school.... i used to skip school to go
down to the local bowling alley... they had about 8 pinball games there...
all the old gottlieb wedgeheads... (mid to late 60's), cowpoke became my
favorite....well fast forward to the mid 90's.... i had a house, was
finishing my basement, and looking for my favorite game... yup..
..cowpoke.... I went to nj to a show... .none there... went to local
distributors, they told me to find a collector who was willing to part with
one... also told me to go to chicagoland which is an area that twice a year
has nostalgic stuff including old coin operated games.... didnt find wone
there either, but ran into someone that had one... he sent pics, but the
playfield was beat... right down to the wood....well as it turned out, there
was a local show about 2 miles from my house... went there and guess what? i
found one... but the guy didnt want to part with it... until imade him an
offer he couldnt refuse... yuip.. paid lots of money for it, but ya know
what? I can still make a grand on it today if i sole it....why? its one of
the most sought after games.... don't ask me why, maybe they made very few
of them... one reason (and i would ned a whole nother hour) is basically
only three states had games made for them because they were considered
gambling.... manufacturers gout around this law by making whats known as an
add-a ball game.... like the replay version, but instead of rewarding games
for score, it added balls for score.... so there were few of alot of games
of that era that were made....it's a pretty fascinating hobby (the history
about it i mean), how it evolved etc....i had between 80 and 90 games...
most are gone...i had them everywhere... in the garage.. at my shop, at my
neighbors (who didnt seem to mind), out on location.... i am down to between
25 and 30 right now.. .all set up in the basement to play!! So you would be
surprised what games are worth and which ones arent worth much....
Its kinda like bike building... and what american chopper or Orange
county choppers did for motorcycles.... the market has changed so
much...with arcades dropping like flies, ther became nowhere to play
anymore...only a few games at certain places, so people started buying them
for themselves... so now alot of people have them at home and everyone is a
pinball techy... lol they want to buy, fix, and resell for profit... one
reason i got out of it... most did hack jobs on the machines... is why i
said im glad we have people like that fixing machines.. it keeps us guys
busy with work.... lol
No vincent huh?? Its been years since i've even seen one, let alone
work on one...

Fwed

 

Not quite. The bike ran on three for three rides, and then it fixed itself
as I rode it around more (~4 miles).

I think this is the issue. However, all the race (solo seat) bodywork must
be taken off to get at the engine, and since the first 4 miles, it has
behaved very well, starting up and running smoothly as before on all four.
Thanks for the suggestions, and I'll know where to look if it happens again.