Rain And A Rough Running 125

Blog Date - 07 March 2012

It's getting old my poor poor 125...

I love my 125.  It's a Honda CLR 125 City Fly, it's really a road bike but it looks like a trailie, it's now old and dirty and a little battered but it's mine and it's my baby! I've had it about 3 years now and I've put 26,000 miles on her bringing the total mileage to 36,000 miles.  Over the last 6 months though she's developing a problem that's getting worse.

I've ridden the bike through -5 degrees of cold and frost and fog and never missed a beat.  I've ridden her on the hottest days in summer without a care in the world.  But when it rains she coughs, splutters and stalls.  "Electrical" I hear you all cry, almost in unison. Normally I'd agree, but there is a quirk, a twist in the tail.  I'll be riding along fine, then I'll feel the motor lose power, come back, lose and come back.  I know it's coming.  I'll stop at some lights and sure enough no amount of revving or preying will keep her going.  Yet...if I put the choke on...she'll start just fine and carry on for another few yards before coughing as we travel along.  It "FEELS" like carburation, fueling and temperature rather than a dodgy connection.

You see...in my thinking if it was electrical it would make no difference whatsoever the use of the choke.  If the HT lead is shorting out, if the kill switch is giving up or if the side stand switch is waterlogged then the choke will not help it start.  Or would it...?  I can see a reasonable argument that if there is not necessarily a short but a high resistance somewhere in the system then this could lead to a weak spark, and that weak spark is enough for dry weather but when the motor is cold it may not be enough.  But the motor starts from cold no problem at all.  It could be a dodgy connection.

Is it possible there's water getting into the air/fuel mixture?  I mean everything else works perfectly until water is added.  Is there a hole in the airbox that's sucking in water?  When it's dry this hole makes no difference to the air and fuel, but if there's water coming in there then this will kill the spark plug, super-cool the engine and cause all other kinds of problems.  It's actually quite possible.  I've had the motor out last winter and there may be a gap between the carb and the airbox, I may have forgotten to replace a pipe somewhere or maybe there's a big old crack in the airbox. 

The idea that the water is super-cooling the engine makes a little sense.  This morning if the bike's running sub 25 miles per hour it was ok, when I got it onto the motorway and above 50 it cleared up.  It's keeping in that middle everyday speed that seems to be the problem, oddly enough especially into a head wind! Is the flow of water across the motor causing the motor to run very cool? Riding in minus 5 is chilly, but there's only air that’s cooling the motor and air is a good insulator, water on the other hand is an excellent coolant, especially water that is evaporating, such as the steam that pours off a hot engine.  Honda ain't stupid, the bike and the motor are designed such that this will still keep the motor in an operating temperature, but perhaps there's something worn out that can't cope with the cool motor?

We go on and on and on and on and on and on and on and on and on and on about how bad the weather is in the UK.  This has been a problem on my bike for 6 months now, and this is the third time it's been raining enough for this problem to arise.  Don't blooming well tell me it's always raining in the UK and how terrible life is for us poor poor bikers.  So how do I solve this problem? 

First off, always start with the cheapest!  I'll take time to look at the airbox, air filter, carburettor and inlet manifold.  I'll see if there are any potential air leaks that could be sucking in the rain.  I'll also replace the spark plug.  I have an iridium spark plug that's been in there for 25,000 miles.  They're supposed to last for 50,000 miles, but that's in a low revving car not a 125 that gets thrashed down the motorways at 9,000 rpm.  If nothing else she deserves a new spark plug anyhow.  Maybe that spark plug is worn such that it can't operate in the cold temperature of a wet motor.

Then I'll wait until the next bout of heavy rain.

If the problem's still there I'll try disconnecting or bypassing the side stand switch, the kill switch and even the ignition switch.  One thing I've learnt over 22 years of Honda ownership...never trust the ignition barrel.  If none of that helps I could always see about bypassing the whole lot and powering the computer directly, but I hope it does not come to that.  Of course in a perfect world I would do one thing at a time...ride the bike...see if the problem is fixed and then move onto the next item until I find the issue.  That however means lots of waiting for the rain and lots of coughing a spluttering rides to and from work or important meetings until I find the issue.  Grrrrr!

There are a myriad of potential problems, it's perfectly possible it's not one single problem either, it may be 2 parts or 1 part and one problem that combine to form the poor running.  Diagnosis of a problem that comes and goes, is intermittent even when it is raining, is ALWAYS a nightmare to solve.  I fix computers for a living, I can't fix someone's problem when I'm there and the problem's not happening.  I hate intermittent problems, I really do.
 

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