OT motorcycle won't work in rain, any pilots out there?

[default]

Have you checked that the kill switch is not intermittent
or shorting when wet?

Hopefully it is shorting when wet. This kill switch doesn't short the
coils to ground the way some MC's do it. This kill switch has to
carry the 12 volts from the ignition circuit (battery,key switch and
fuse) to one side of both coils. The transistor switching modules
take the other side of the primary coil windings to ground to make a
spark.

The kill switch seems to work OK. I tried pressing and switching it
when wet with no difference in operation - other than switching it
"off" does stop the engine. Switch is a single pole rotary with two
off positions and one on position in the center.

 

[default]

Sounds like you found the problem ;-)

Certainly fits your starved fuel symptoms.

...Jim Thompson

It certainly would if I only had one carburetor. With this MC my
usual SOP is to turn off the fuel a mile from my house using the
petcock on the tank the bike will continue to run on gas in the float
bowls for that long.

The engine leans out a lot and may not idle without stalling, but will
run at partial throttle and wide open - different symptoms than the
wet condition - won't go a mile when wet, won't run wide open,
partial, or idle. Problem first kicks in during partial throttle
between 20 and 70 MPH - haven't really tried running 15 mph in the
rain so can't say if it will maintain that speed without quitting. I
don't drive over 60 in rain as a general thing.

When the float bowls are running out of fuel the level drops, but
there's still fuel. It may run rough but continues to run. Opening
the throttle tends to suck more fuel even with a low float bowl
levels.

 

[Rich Grise]

No amount of spraying water over the engine, ignition etc.. will cause
it to fail in the driveway. I can dump buckets of water on the
ignition and engine without it dying. Even a mist of water from a wet
road will cause it to die and rain causes it to die faster.

Hold your sprayer nozzle at the ground and spray upwards.

Good Luck!
Rich

 

[Tim Wescott]

I posted the problem with my 81 Honda back in April and it has only
just rained once since then, so I took the bike out to see if the new
wires and spark plugs and caps helped.

I did eliminate one possibility before the rain stopped - venting the
fuel tank didn't correct the problem so it wasn't a vacuum forming in
the fuel system.

This time I was starting out with a cold engine, full tank of gas, and
it was really raining hard. I didn't go more than two blocks before
the engine started running rough, applying choke caused it to smooth
out and run normally, turning off the choke caused it to run rough
again, that worked through several cycles. Eventually I let it get
too rough and it died. I coasted for about 30 seconds engaged the
engine and it fired right up. This seems to work about as well as
stopping to rest - engine will always start after a short rest.

I should have tried riding at very slow speed to see if it would keep
going - but didn't think of it when I had the chance.

No amount of spraying water over the engine, ignition etc.. will cause
it to fail in the driveway. I can dump buckets of water on the
ignition and engine without it dying. Even a mist of water from a wet
road will cause it to die and rain causes it to die faster.

At this point I'm almost ready to give up on an ignition problem since
all the ignition except the transistor switches and pick up coils have
been replaced. And the likely hood of two independent electrical
systems failing seems too extreme. All the electrical parts have been
drenched with water and it runs if the bike is stationary.

My latest and greatest theory is carburetor icing. From what I read,
the conditions are favorable - humid between 20-70F sometimes up to 80
F. The problem is more likely to occur when the engine is cooler. It
is more likely to occur when backing off on the throttle.

Where it doesn't fit the theory is that using the choke should
exacerbate the problem - it doesn't seem to, and while the engine is
relatively cool and the problem is occurring it actually helps. When
the engine is at full operating temperature the choke is less likely
to help it.

I can't get the problem to occur when the bike is stationary, it has
to be moving through airborne water in the form of rain or mist (we
don't get enough fog here but I suspect a heavy fog might kill it
too).

My engine is adjusted too lean according to the color of the spark
plugs. With "normal" carburetor icing this shouldn't exacerbate the
problem - according to what I read. I didn't change the jets but did
put in a less restrictive exhaust when the old one had holes in it -
the problem did occur with the old exhaust but with holes in it so I
can't say for certain mixture isn't involved somehow.

Any one with more ideas on troubleshooting this problem? Can it be
carb ice with richening the mixture making it better? All I read says
it should get worse as the mixture is rich, since they assume that the
airflow is too restricted. But as the mixture is made rich, I could
see where there may be less evaporative cooling from the gas since the
gas should evaporate slower with humidity and gas concentration
rising.

Have gas formulations changed in some way that might account for it?

I used to be able to keep going in torrential 30 foot visibility
without it missing a beat - now it won't go more than two blocks in
rain.

Once at highway speed, especially when going fast it seems less
susceptible but backing off the throttle then, in rain, will almost
always kill the engine.

If you can get the air cleaner off fast enough, and if you can see in
the carburetor throats, stop and take a look when it dies -- sometimes
you can see the frost melting away (or not, if it's cold enough). This
makes a nice definitive check to your frosting problem. If your intakes
are fairly well protected from direct road grime, it may even be worth
while to do a couple of runs without the air cleaners on their at all,
if it means being able to see your venturis quickly.

A friend of mine was recently telling me about a hot rod motorcycle he
built when he was a kid -- he'd shimmed the cylinder on the case to
change the port timing, with corresponding shaving done to the head,
he'd put on bigger carbs, and to top it off he was running
methanol/nitro (on the street, no less).

He said that after a half hour of running fast the carburetors were
sitting in big balls of ice. Now _that's_ obvious carburetor icing!

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Posting from Google? See http://cfaj.freeshell.org/google/

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html

 

[Tim Wescott]

The reason that 'carb ice', is rare in cars and bikes, compared to in
planes, is twofold. The first is that it is normal in these vehicles to
heat the carburator to prevent it (this has the 'downside' of slightly
reducing engine efficiency), and the second is that it is rare to run for
prolonged periods at steady throttle settings (and particularly at low
throttle settings).
Fuels have changed, modern stuff, often contains ethanol, which can make
this much worse. However your problem sounds 'extreme'.
Has the fuel system been fully drained (if the fuel was left standing for
a while, it can pick up moisture).
Does the bike have any system to heat the carburettor, or the incoming
air?. Is this working?. If the bike is water cooled, then it may be like
the common system in car engines, with a thermostatically controlled water
jacket on the inlet manifold. If this ad stopped being heated, it'd
explain the problem.
Some aero engines, accept the slight loss of efficiency involved, and pass
the inlet in through the warm oil in the sump (Lycoming units), making
them _much_ less likely to have problems. Compared to a Continental engine
without this, carb ice is perhaps 50* less common...
The choke, shouldn't help, but if there was physical ice in the venturi,
movement here, could simply displace the ice. However I'd be much more
suspicious of the actual fuel jet being where the problem lay. Perhaps
icing here, which leans the mixture off even further, letting the choke
help.
Historically, this was more of a problem in some countries, and in the
past there was a different carb/inlet setup, supplied in some countries to
help with this. You might want to look and see if there is such an
alternative installation on your machine.

I used to own a '69 Toyota Corolla. It was obviously a California car
originally (it had the air pump), and it had _no_ carburetor heat. It
would regularly ice up going over the coast range in the winter in
northern Oregon.

While the Toyota engineers had not provided the car with carburetor
heat, they were thoughtful enough to make the ignition key just a hair
smaller than the venturi opening. I could go 20 miles, stop, remove the
air cleaner, poke the key in the venturi to knock off the ice, put the
air cleaner back on, drive 20 miles...

Fortunately I usually only had to do that a couple of times each trip.
I think I ended up jury rigging carburetor heat on the thing.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Posting from Google? See http://cfaj.freeshell.org/google/

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html

 

[Jim Thompson]

[snip]

If you can get the air cleaner off fast enough, and if you can see in
the carburetor throats, stop and take a look when it dies -- sometimes
you can see the frost melting away (or not, if it's cold enough). This
makes a nice definitive check to your frosting problem. If your intakes
are fairly well protected from direct road grime, it may even be worth
while to do a couple of runs without the air cleaners on their at all,
if it means being able to see your venturis quickly.

[snip]

Years ago I coasted down that long hill down the west side from Jerome
(AZ)... in a 1964 Dodge Dart.

At the bottom I applied throttle... nothing. Pulled air cleaner... it
was completely full of snow-like ice crystals ;-)

...Jim Thompson

 

[Meat Plow]

Hopefully it is shorting when wet. This kill switch doesn't short the
coils to ground the way some MC's do it. This kill switch has to
carry the 12 volts from the ignition circuit (battery,key switch and
fuse) to one side of both coils. The transistor switching modules
take the other side of the primary coil windings to ground to make a
spark.

The kill switch seems to work OK. I tried pressing and switching it
when wet with no difference in operation - other than switching it
"off" does stop the engine. Switch is a single pole rotary with two
off positions and one on position in the center.

Have you checked your alternator output. I've owned two 1981 CB750F models
and both had alternator problems. One I bought new and the one I still
have I bought in 1999. Both had under 6000 miles on them when one had a
short in the rotor and the one I have has a short in the stator. I can't
buy a new stator, discontinued. But I am thinking of having a place that
rewinds small motors and all sorts of things give it a try. One thing is
the 750 motor needs 13.8 volts or it will sputter and spit. However it
wouldn't cause it to die unless the battery was down and I don't think
this is your case. But check the output voltage none the less.

 

[Marra]

I posted the problem with my 81 Honda back in April and it has only
just rained once since then, so I took the bike out to see if the new
wires and spark plugs and caps helped.

I did eliminate one possibility before the rain stopped - venting the
fuel tank didn't correct the problem so it wasn't a vacuum forming in
the fuel system.

This time I was starting out with a cold engine, full tank of gas, and
it was really raining hard. I didn't go more than two blocks before
the engine started running rough, applying choke caused it to smooth
out and run normally, turning off the choke caused it to run rough
again, that worked through several cycles. Eventually I let it get
too rough and it died. I coasted for about 30 seconds engaged the
engine and it fired right up. This seems to work about as well as
stopping to rest - engine will always start after a short rest.

I should have tried riding at very slow speed to see if it would keep
going - but didn't think of it when I had the chance.

No amount of spraying water over the engine, ignition etc.. will cause
it to fail in the driveway. I can dump buckets of water on the
ignition and engine without it dying. Even a mist of water from a wet
road will cause it to die and rain causes it to die faster.

At this point I'm almost ready to give up on an ignition problem since
all the ignition except the transistor switches and pick up coils have
been replaced. And the likely hood of two independent electrical
systems failing seems too extreme. All the electrical parts have been
drenched with water and it runs if the bike is stationary.

My latest and greatest theory is carburetor icing. From what I read,
the conditions are favorable - humid between 20-70F sometimes up to 80
F. The problem is more likely to occur when the engine is cooler. It
is more likely to occur when backing off on the throttle.

Where it doesn't fit the theory is that using the choke should
exacerbate the problem - it doesn't seem to, and while the engine is
relatively cool and the problem is occurring it actually helps. When
the engine is at full operating temperature the choke is less likely
to help it.

I can't get the problem to occur when the bike is stationary, it has
to be moving through airborne water in the form of rain or mist (we
don't get enough fog here but I suspect a heavy fog might kill it
too).

My engine is adjusted too lean according to the color of the spark
plugs. With "normal" carburetor icing this shouldn't exacerbate the
problem - according to what I read. I didn't change the jets but did
put in a less restrictive exhaust when the old one had holes in it -
the problem did occur with the old exhaust but with holes in it so I
can't say for certain mixture isn't involved somehow.

Any one with more ideas on troubleshooting this problem? Can it be
carb ice with richening the mixture making it better? All I read says
it should get worse as the mixture is rich, since they assume that the
airflow is too restricted. But as the mixture is made rich, I could
see where there may be less evaporative cooling from the gas since the
gas should evaporate slower with humidity and gas concentration
rising.

Have gas formulations changed in some way that might account for it?

I used to be able to keep going in torrential 30 foot visibility
without it missing a beat - now it won't go more than two blocks in
rain.

Once at highway speed, especially when going fast it seems less
susceptible but backing off the throttle then, in rain, will almost
always kill the engine.

Its definitely a fuel problem as pulling on the choke fixes it.
Sounds like shit in the carb or fuel system somewhere.

 

[default]

Have you checked your alternator output. I've owned two 1981 CB750F models
and both had alternator problems. One I bought new and the one I still
have I bought in 1999. Both had under 6000 miles on them when one had a
short in the rotor and the one I have has a short in the stator. I can't
buy a new stator, discontinued. But I am thinking of having a place that
rewinds small motors and all sorts of things give it a try. One thing is
the 750 motor needs 13.8 volts or it will sputter and spit. However it
wouldn't cause it to die unless the battery was down and I don't think
this is your case. But check the output voltage none the less.

Well I can try unplugging the alternator and running it in rain the
next time it rains. It will start and run without an alternator. I
could see how noise on the battery could cause the trigger point of
the transistor switch to shift and cause a misfire.

This one did have a shorted rotor. I took it out and rewound it and
added an expanded scale voltmeter to watch it. No amount of water in
the alternator housing will cause the problem when it is stationary,
but it is easy enough to unplug so the next time it rains I'll try
that.

Actually you can buy rotors both rewound with a core charge, and brand
new for about the same cost ~$70 last time I checked. Place over in
England is manufacturing them and with shipping the cost was
comparable to buying one rewound in the US. I had a quote of $300+
from the Honda shop so spent $50 on a 6# spool of 22 AWG magnet wire
before I discovered I could get a new one. My rewind works well.
There's a little bit of run-out because the slip rings are a little
crooked but it has been running fine that way. There's still enough
left over magnet wire to wind several more (takes about 12 ounces of
wire for a rotor)

I also found a source for a new stator for it for a few hundred
dollars. I don't need a stator though - and it looks easier to rewind
than the rotor I already did.

That rewinding stuff isn't that tricky. Stators are wound on formers
external to the poles then put in place and epoxied in. Rotors are
more hassle - take apart the pole halves with a large gear puller, and
scrape out or unwind the wire.

I have used two techniques for the coils - a bobbin made of very thin
PCB material and soldered together then just insulate it and fill it
with wire brushing on epoxy as you go (the bobbin could be almost
anything including cardboard or tin can material - just has to be
strong enough to hang together long enough to mount and epoxy it in,
and thin and insulated.

Technique two is to just wind a "self supporting coil." Build/make a
two part wood mandrel of about the right size, then cover the wood
with Teflon plumbers tape (for a mold release agent). For the sides I
use a pair of polyethylene can covers like one sees on Planter's
Peanuts, cut an undersize hole and slip it on the mandrel. Brush it
with a light coating of machine oil (mold release again), then just
paint the core with epoxy and wind adding epoxy after each layer or
two (the epoxy creeps out between the lower windings so it isn't
necessary to do after each layer). Let set then pry it off the
mandrel. I add a layer of cloth soaked in epoxy to the pole pieces to
keep it in place and protect the sides. Only caveat is to carefully
route the wires to the slip ring connections along the pole so they
aren't allowed to move and epoxy in place.

My alternator output is more like 14.4 volts, but it always has been.

 

[default]

f you can get the air cleaner off fast enough, and if you can see in
the carburetor throats, stop and take a look when it dies -- sometimes
you can see the frost melting away (or not, if it's cold enough). This
makes a nice definitive check to your frosting problem. If your intakes
are fairly well protected from direct road grime, it may even be worth
while to do a couple of runs without the air cleaners on their at all,
if it means being able to see your venturis quickly.

There's no good way to get a look inside the carburetors. Too much
junk to remove to get at them. The slides come down when the engine
is off so I'd also have to move them out of the way. Might be worth
running without a filter (not like there's a ton of airborne dust in
the rain) and mounting a mirror in there. I probably only have a few
seconds to stop and look at it because it restarts after a brief pause
most times.

A friend of mine was recently telling me about a hot rod motorcycle he
built when he was a kid -- he'd shimmed the cylinder on the case to
change the port timing, with corresponding shaving done to the head,
he'd put on bigger carbs, and to top it off he was running
methanol/nitro (on the street, no less).

He said that after a half hour of running fast the carburetors were
sitting in big balls of ice. Now _that's_ obvious carburetor icing!

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Obvious would be nice - I've been screwing with it for over six months
now - mostly with the ignition components.

 

[default]

Its definitely a fuel problem as pulling on the choke fixes it.
Sounds like shit in the carb or fuel system somewhere.

Probably not in all four carburetors - this thing runs rough for a
second or two then dies completely, then will generally restart in
about 30 seconds.

So I'm thinking ice now.

 

[Meat Plow]

Probably not in all four carburetors - this thing runs rough for a
second or two then dies completely, then will generally restart in
about 30 seconds.

So I'm thinking ice now.

I think only one carb is choked if I recall. Been awhile.
--
#1 Offishul Ruiner of Usenet, March 2007
#1 Usenet Asshole, March 2007
#1 Bartlo Pset, March 13-24 2007
#10 Most hated Usenetizen of all time
#8 AUK Hate Machine Cog
Pierre Salinger Memorial Hook, Line & Sinker, June 2004
COOSN-266-06-25794

 

[default]

I think only one carb is choked if I recall. Been awhile.

You are probably thinking of the accelerator pump diaphragm. That is
on only one carburetor. Choke is a single cable that links to choke
plates on all carbs.

 

[Jeff L]

You are probably thinking of the accelerator pump diaphragm. That is
on only one carburetor. Choke is a single cable that links to choke
plates on all carbs.

Those bikes have a accelerator injector in each carb - the pump is located
on one of the middle two carbs. Cracking the throttle several times quickly
should give it a couple of good shots of gas - if it responds well to that
(and doesn't run really bad from the terribly rich mixture), then it is very
likely a fuel starvation problem. Another thing to check is cracked rubber
boots between the head and the carburetors.

--

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[default]

Those bikes have a accelerator injector in each carb - the pump is located
on one of the middle two carbs. Cracking the throttle several times quickly
should give it a couple of good shots of gas - if it responds well to that
(and doesn't run really bad from the terribly rich mixture), then it is very
likely a fuel starvation problem. Another thing to check is cracked rubber
boots between the head and the carburetors.

My accelerator pump is on the #2 carburetor. I'll try pumping it in
the rain.

There's an air cutoff diaphragm on the #1 carburetor

The carb to head rubber hoses appear to be intact. Pulling them is a
royal pain so I'm not anxious to do that except when absolutely
necessary. I did inspect them visually and did spray water at the
junctures and all around the carbs from a stream to a mist.

I did discover something that I haven't been maintaining properly.
Apparently my bike has an exhaust gas re circulator system, comprised
of a lot of tubing and a reservoir. It feeds into the air box after
the filter. Says to check it every 4K and I have never checked it.
There's a drain for the reservoir. also says to drain it more
frequently when riding hard or in the rain . . .

 

[joseph2k]

My accelerator pump is on the #2 carburetor. I'll try pumping it in
the rain.

There's an air cutoff diaphragm on the #1 carburetor

The carb to head rubber hoses appear to be intact. Pulling them is a
royal pain so I'm not anxious to do that except when absolutely
necessary. I did inspect them visually and did spray water at the
junctures and all around the carbs from a stream to a mist.

I did discover something that I haven't been maintaining properly.
Apparently my bike has an exhaust gas re circulator system, comprised
of a lot of tubing and a reservoir. It feeds into the air box after
the filter. Says to check it every 4K and I have never checked it.
There's a drain for the reservoir. also says to drain it more
frequently when riding hard or in the rain . . .

That could be a factor or even the cause. My money is on contamination in
the gas tank that is moisture sensitive somehow. My recommendation: drain
and flush the gas tank and hoses clear to to the carburetor connection,
drain the carbs as well, replace the fuel filter, and put it all back
together and refuel with fresh, known clean, gasoline. Do not reuse the
fuel removed from the tank, just dispose of it.
When i was much younger i saw a similar problem with a lawn mower, a little
different though it would just stop at about half a tank of gas. Took me
months to find the problem. With the drained fuel was placed in a glass
container you could see the contaminated layer in it though.

 

[default]

The reservoir looks like it holds about 6 ounces maybe more with the
tubing and I drained what appeared to be about 2 ounces of clear water
out with only a faint hint of oil (light sheen) on it.

That could be a factor or even the cause. My money is on contamination in
the gas tank that is moisture sensitive somehow. My recommendation: drain
and flush the gas tank and hoses clear to to the carburetor connection,
drain the carbs as well, replace the fuel filter, and put it all back
together and refuel with fresh, known clean, gasoline. Do not reuse the
fuel removed from the tank, just dispose of it.
When i was much younger i saw a similar problem with a lawn mower, a little
different though it would just stop at about half a tank of gas. Took me
months to find the problem. With the drained fuel was placed in a glass
container you could see the contaminated layer in it though.
--

I've dealt with a few recalcitrant outboards that got a contaminated
load of fuel - haven't had one die like this though. Outboards use
multiple carbs.

I've been draining fuel looking for contamination. Each carb has a
drain at the very bottom of the float bowls - I drain it into a glass
jar and see nothing but gas - even after being in the rain. Not a
speck of rust or water - and even if there were, the fuel supplied to
the cylinder is from the top of the float bowl, so if there were
enough contamination there I should see it, or if the level was so low
as to cause it to stop I should see that too by draining the bowls.

Four carburetors dying all at the same time quickly? Then restarting
again after a 30 second pause? only to die again? When I
deliberately cut the fuel off and drive, it takes close to a mile for
the bike to stop - then it usually works fine except may die when
idling. Even when it seems totally out of fuel it will still fire
intermittently - this problem is rough running for a second or two and
total death on all four cylinders immediately after. Adding choke may
make it run for awhile longer.

Those symptoms would seem to rule out interrupted fuel supply - the
onset of death is too quick.

I can pull in the clutch and coast for the 30 seconds it takes to
restart which leads me to believe it isn't water being thrown up into
some sensitive part from the road surface like someone suggested.

Plan A is to go back to the ignition system - I think I've ruled out
water in most of the system. Right now I plan to add some LEDs to the
ignition coil primaries. Looking for ways to steal a little energy to
light a led only when the coil is firing and do it without an active
circuit, and monitor the failure should one occur - does the primary
stay high, or low, is the primary power there or not- Five LEDs
should do it.