carbon fouling, right cylinder not firing, stalls under load

gosh ...

Took my old Honda twin out for a test ride after cleaning the plugs with
400 grit sandpaper. After driving 40 mph for a mile, noticed poor power
when accelerating from a stop, and the engine stalled and was hard to
start. Returning home, I removed the plugs. The right one was not too
hot to be held by the threads with bare fingers, but I couldn't do that
with the left. Also the left pipe was very hot, but the right not so
hot. Left plug was dry and carbon fouled. Right plug was not as
fouled, but was wet with gas.

I recall having a similar problem 20 years and 6000 miles ago with the
same bike, and it was resolved by installing a new battery. I have a
new battery in it now though.

I am thinking the timing may be off, although I just put in new points
and thought I had the timing set correctly.

My other guess is a problem with the centrifugal advance.

Please advise as to whether either of those guesses is consistent with
the symptoms, or suggest something else.
========================================
1976 Honda CJ360T (inline twin, SOHC)

 

Left cylinder a little too rich, adjust the idle mixture screw. Maybe
the spark plug on the right cylinder isn't firing at all, or maybe it's
getting far too much gas because of a stuck float or the main jet has
fallen out and is laying in the float bowl or the needle clip is in the
wrong slot orthe idle mixture is adjusted wrong...

How old are the spark plugs? Does the symptom move to the opposite
cylinder if you switch spark plugs? Does gapping the right hand spark
plug tighter help?

Does that engine use two sets of points or one set? Usually the Hondas
would have a master timing plate with one set of points that had to be
adjusted first, and then the other set of points bolted onto the master
plate and they were to be set second...

Did you install new condensors, too, or are you using the old
condensors? Does the right hand set of points spark a lot? It might be
the condensor...

Centrifugal advance would affect both cylinders,if one cylinder's
ignition is advanced or retarded, so is the other...

 

When was the last time it was running right and what happened since
that time ? Was it laid up for a long time ? What parts did you
swap or adjust ?

Taking a wild ass guess, I'd say ignition problem, possibly a plug
wire. You ought to be able to check resistance with a multimeter.

Other suspects might include a crapped up carb, a problem with
a stuck throttle or choke or possibly a valve.

Check your compression, make sure the carb parts move freely and
return to proper position. If it all looks OK, consider a carb
cleaning.

 

Sounds likely. Remember this has a 180 degree crank and so setting the
timing requires a little more thought.

Could be a carb problem but most likely ignition related, especially if
you 've just fiddled with it.

 

I just went over the carbs and cleaned them thoroughly, and I'm pretty
sure I did that part right. The carbs should be good.

I had a similar problem with an old flathead six (stalls under load,
stalls at low rpm). That was fixed by finding and fixing an electrical
leak and putting in a new battery.

 

I think the carbs are okay.

The plugs are old, but they were performing well the past few days.
They have been carbon fouled repeatedly from this same problem. Is it
enough to wire-brush the plug and run some fine sandpaper between the
plug's contacts? I don't see why the plugs would be bad, but maybe
somebody else does ...

Yes, it is like that.

Yes, I put in a new condenser.

I checked and adjusted the points again. There was practically no
grease on the ignition cam. I found that the left was slightly
retarded, and the right was very retarded. The right was firing very
close to TDC. I set the gap on the left points to about 0.38 mm (spec
is 0.30 to 0.40 mm). Then I adjusted the timing as you describe above
(and consistent with the owner's manual). Cranking the engine with the
plugs removed and touching the engine, I saw no spark. Then charged the
battery and I did get good spark on both sides. I got it to run for
about a second, but then nothing. Charged the battery some more and now
I am not seeing spark on either side.

My guess is that the low battery caused poor sparking, which caused the
plug fouling, which caused worse sparking and more fouling. I'm
thinking the low battery might be due to something wrong with my
battery-charging system.

Can you say whether new plugs are likely to help get it started? Then I
could take a closer look at the charging system.

 

I think the carbs are okay.

The plugs are old, but they were performing well the past few days.
They have been carbon fouled repeatedly from this same problem. Is it
enough to wire-brush the plug and run some fine sandpaper between the
plug's contacts? I don't see why the plugs would be bad, but maybe
somebody else does ...

Yes, it is like that.

Yes, I put in a new condenser.

I checked and adjusted the points again. There was practically no
grease on the ignition cam. I found that the left was slightly
retarded, and the right was very retarded. The right was firing very
close to TDC. I set the gap on the left points to about 0.38 mm (spec
is 0.30 to 0.40 mm). Then I adjusted the timing as you describe above
(and consistent with the owner's manual). Cranking the engine with the
plugs removed and touching the engine, I saw no spark. Then charged the
battery and I did get good spark on both sides. I got it to run for
about a second, but then nothing. Charged the battery some more and now
I am not seeing spark on either side.

My guess is that the low battery caused poor sparking, which caused the
plug fouling, which caused worse sparking and more fouling. I'm
thinking the low battery might be due to something wrong with my
battery-charging system.

Can you say whether new plugs are likely to help get it started? Then I
could take a closer look at the charging system.

 

Something happens to old plugs that makes them mysteriously stop firing
even after being cleaned. I suspect that condensation may get way up
inside the spark plug and bleed off what little voltage that builds up
across the gap...

I used to clean old fouled spark plugs and then heat them up over a
burner on the stove to get them hot enough to start the engine. It
really seemed to help...

Wire brushing spark plugs isn't as good a way to clean them as sand
blasting or even using a strategically folded bit of sandpaper to get
deep down into the the spark plug and make the porcelain nice and
white. I used to use 240 grit 3M Wet/Dry sand paper on my 2-stroke
plugs. I would clean the plugs about every week...

The spark will jump from the sharpest edge of the center electrode to
the grand electrode. That's why you want to file the center electrode
flat. You want that sharp edge, round edges take more voltage to fire
and you don't have a lot of voltage with a motorbike coil. You're lucky
to get 9KV to 12KV out of a motorbike coil, and this makes the engine
very sensitive to fuel/air mixture ratio, especially during cold
starts, when you need a rich mixture...

If a nice strong 35 KV car coil will jump a 1.25 inch bright blue spark
to ground, a 10KV motorbike coil should jump a 0.25 inch spark to
ground if your battery is all charged up and your ignition points are
clean...

Motorbike electrical engineers working with high RPM engines need to
make a compromise between having a lot of voltage at the plug gap, or
having an ignition coil that builds up voltage rapidly at the gap...

Most shade tree engine tuners imagine that having a coil that produces
Gawd's Own Lightning is a wonderful thing, but it's not. A spark plug
will fire when there is just enough voltage at the plug gap to overcome
air pressure in the cylinder. Even if you have a coil that puts out
35KV to 50KV, the plug will still fire when the voltage overcomes the
pressure...

A high inductance ignition coil may take over 45 microseconds to rise
to that level, and voltage gets short circuited across the nose of the
spark plug's insulator so a lot of it is lost...

45 microseconds is the maximum tolerable amount of time the voltage
rise can take place in, otherwise you run into plug fouling problems...

Voltage rise time is related to the mass of iron in the ignition coil's
core, and the physical dimensions of the copper windings in the coil.
Big heavy coils like car coils build up their voltage slowly and it can
get short circuited to ground if the plugs are dirty. That's why we
clean plugs and regap them...

A big heavy car coil for a V-8 only needs to produce 2500 sparks per
minute at 5000 RPM. There's lots of time for voltage rise to take place
at the spark plug gap...

A motorbike engine may turn 10K RPM or even higher, so there's less
time for the voltage to rise and jump the plug gap. Each little coil
has to fire twice as often, 5000 times per minute, or more. So
motorbike coils are small and have low inductance and the voltage rise
time is faster. That's why motorbike electrical engineers specified
those tiny ignition coils.

It might be low battery voltage. Ann ignition coil is just a DC
transformer. It works off of the collapse of the electromagnetic field
in the primary winding to induce a higher voltage in the secondary
winding...

If you have a good solid 12 volts going into the primary winding with
enough current to saturate the iron core with magnetic flux, and you
need
to have 10KV come out of the secondary winding, you need 833 turns of
fine wire on the secondary side for every 12 turns on the primary
side...

If the motorbike has been sitting around in a damp place, moisture
might
have gotten into the coils and shorted some of the secondary winding to
ground. If you can set the motorbike in the sun with the gas tank off,
maybe you can bake some of the moisture out of the coils...

Well, spark plugs are only about $2.50 apiece. It's worth trying. Your
Honda must be worth $5.00 to get it running. Same thing with the
battery. Maybe a new one is $40.00 or less. A new battery every two
years isn't too much for your beloved motorbike to expect, is it?

 

Thanks much for the ignition info. I thought the bike was worth at
least $5, but I am starting to wonder ... The case is getting stranger
and stranger.

I just put new plugs in and now it is running on only the right
cylinder. Previously I was running on only the left. After driving a
mile, I took out the left plug and it looked like new, no gas or soot or
ash on it at all, and the left pipe was cool.

My left plug wire showed some damage where the boot joins to the wire,
so I decided to replace the terminal and boot---please see my new thread
on that topic ...