one spark plug is black

hi everyone,my name is stan and i'm new to the forum.been reading for quite a while and decided to ask a  question.my s-wing is a 2008 one with 57500 miles on the clock.some time ago it started taking more fuel,i had k&n air filter and ir.ngk,went back to stock but not much luck..today i had the plugs changed again and the left one was quite black and the mechanic said running rich,the right plug was good.i asked him what the options were and he told me to try some fuel cleaner..i think there must be more to this.fuel cleaner would make sense if the bike has been sitting around and mine has been used daily,about 30000 miles in the last year..i just read about fuel pressure regulator..could that be the problem,thanx in advance,ride safe:-)

I would think that a faulty fuel pressure regulator would effect both cylinders. I would look towards the source of spark to the rich cylinder. I think you would be wasting your money on fuel cleaner. JMHO.

Hi Stan.
A lousy running Swing is a bummer.
I agree, a faulty fuel pressure regulator would likely affect both cylinders, AFAIK.
On the Swing engine, the one ignition coil feeds both spark plugs simultaneously. Both plugs fire every revolution of the crankshaft. Since one plug is clean and the other not, I would suspect a poor connection to the rich running plug, either at the plug's cap or at the coil. You could pull and ground both spark plugs, crank the engine, and observe the blue spark across the electrodes. Both plugs should have a healthy blue spark, but they will have it on alternate crank revolutions. I could get into the reason why, but it is irrelevant right now.
You could also have a faulty coil. You can check the coil with a digital VOM (p. 19-3 service manual), but you also need a peak voltage adaptor, not something that's lying around in your toolbox (not mine either). The minimum coil peak voltage is 100V. Check the plug wires to start with. To totally rule out the fuel pressure regulator, pull both vacuum lines leading from the T-fitting at the intake manifold and check for raw fuel in those tubes (engine off). If you see any fuel in any vacuum tubes, then you can blame the pressure regulator.
You could also have a vacuum imbalance between the cylinders. Is your curb idle steady at 1300 rpm, or does it dance around? Check the vacuum by doing a throttle plate synchronization. That tool you should have in your toolbox, very handy and not expensive as speciality tools go.
I also think you need a new mechanic.

thanx for your replies,i forgot to mention that a month or so ago i've noticed that the idling was a bit low(900) and increased it to around 1100-1200rpm,i did that thinking that it might start to cut off with the weather getting colder..as i said new plugs yesterday and i'm servicing the k&n air and putting it back tmrow..

k77stan wrote:

thanx for your replies,i forgot to mention that a month or so ago i've noticed that the idling was a bit low(900) and increased it to around 1100-1200rpm,i did that thinking that it might start to cut off with the weather getting colder..as i said new plugs yesterday and i'm servicing the k&n air and putting it back tmrow..

Could you have mistakenly changed the fuel mixture when you adjusted the idle? I would re-sync your intake.  Before you adjusted the idle, did you notice the condition of your plugs?

hi Wayne, i turned the correct screw,i'm sure about that as i'm aware which is which..i havnt paid attention to the conditon of prevuious spark plugs..rode the bike today..goes fine but quite juicy:-(

I know this was a year ago but my Swing is similarly black on both plugs and drinking petrol.

@k77stan did you ever resolve your problem?

gilesmdavis how many miles on your scooter and when was the last time you checked your air filter? The first thing I check is the air filter if my mileage goes down. If the air filter gets dirty it acts like a choke, if it can't suck air it'll suck gas.

Ah, hah, yes the mileage. Who knows - claimed 7k (km) but it's an 03 plate. That's a story for another thread.

Changed the filter this afternoon - disappointingly the existing one was in good condition, quite clean. Put a new one in anyway, will keep other as spare.

Back on the age though, that's why I suspect the regulator might be the culprit - as it may have been standing for a while.

You could also have a bad intake valve stem seal on the cylinder that housed the dark plug and/ or you could have worn oil control rings in that cylinder----or it could be a bad plug--it happens.

Sam

Hi all, I have a similar problem with my FJS400 and my mechanic is scratching his head. My wing was stolen late October, its was only taken around the corner and spent the night on its left side in the rain. Luckily no significant damage.  Shortly after, and possibly unrelated, it would sputter when started from cold for about 30 seconds then it would run fine all day. At the end of December it sputtered and flooded. My mechanic changed the spark plugs, which were black, and everything was fine for a week, then it flooded again. My mechanic looked for a fault but everything appeared fine and the bike was running well. He kept it for a week, starting it each morning, to confirm and it flooded again after a week.
He has changed the spark plugs, replaced the air filter ad checked the fuel system. Both the automatic choke and the fuel pressure regulator have been checked and appear to be functioning correctly. There are no warning lights when the bike floods. The bike either runs faultlessly all day or floods when started from cold. The bike is an Italian 06 with 8000 miles and was stored for around 5 years before I bought  it 1 year ago. It has been faultless and used most days for the past year.
Any advice appreciated.

You might have a clog fuel injector from sitting to long .I put fuel injector cleaner every 3 or for 4 tank full,that might solve the problem .your fuel tank might need some cleaning from sitting to long.Try and see if that clears things up . you can try hotter plugs to clean out any carbon that might be stuck on the injector. Water sprayed in the intake when engine is hot and running will clean any carbon stuck to the cylinder head.

Seeing as this is an intermittent problem, you can rule out clogged fuel injectors. I would be looking for an intermittent electrical sensor problem. The electrical sensors that affect the ECM's fuel output would be a  good starting point, in particular the MAP (manifold absolute pressure) and IAT (intake air temperature). I would suggest your mechanic check those two sensors first, but only when the flooding problem manifests itself again. Check for proper electrical contact with the harness, and then check for the proper sensor operation using the service manual and a voltmeter.
Either of those sensors or their operation could have been affected by the bike laying on its side in the rain for an extended period.

Considering that it was laying on it's left side in the rain you might think about pulling the left panel and disconnecting the two wire harness plugs on the ECM to clean the terminals on both the harness plugs and ECM with contact cleaner. Corrosion on those terminals might contribute to the erratic problem you are experiencing.

However that would not explain only one plug being fouled.

Another thought: You might also want to disconnect the FI wire harness plugs and use contact cleaner on both the injectors terminals as well as the FI harness plug terminals.

Tim

Tim, I think you didn't realize that the title of the thread is different than the symptoms described by Gary Hodge in his post today. He is complaining that both plugs are fouling intermittently.

I also wonder if and how his mechanic checked the integrity of the fuel pressure regulator:

"Both the automatic choke and the fuel pressure regulator have been checked and appear to be functioning correctly."

Sometimes a pinhole leak is not visible to the eye. Perhaps Gary should still throw in a new fuel pressure regulator for good measure if his mechanic can't nail the problem to poor connections at the harnesses and sensors.

Both plugs fouling intermittently? I would change the plug wires. They may have deteriorated (electrically) allowing some voltage to ground to the engine before reaching the plugs. Insufficient voltage equals weak spark equals fouled plug.

Be sure to use OEM plug wires for your model. I have a buddy who was experiencing "Wont Start" and 'fouled plugs' even to the point of leaving him stranded hunderds of miles from home. That happened several times and his SW was dealer-serviced every time. Eventually one dealer replaced the coil but didn't have the correct plug wires on hand so they robbed a set from another Honda 600 to get him back on the road. A month later similar plug fouling problems started again. We replaced those 'other Honda' plug wires with the correct ones for his FSC600 and he lived happily ever after.

Tim

PS: The plug wires are dirfferent lengths. Somehow (see above) incorrect lenghts of plug wire will effect operation --maybe too much resistance. The spark plug caps screw on to the spark plug wire, and the other end screws on to the coil with 'waterproof' caps.