Spark plugs

[John Luciano]

If you removed a plug from your bike and it was soot black after 10 miles, what would you look at. They have re jetted the carb, cleaned them swapped floats , dropped the needle as far as it would go. They thought it was ignition . I said the plug is firing or it would not be black it would be wet. It is a 1,600 Suzuki 1999. The rear plug is firing perfectly(common air filter so that aint it.) Ok jump in the season is getting short.

[ThirdWheel]

Carbon deposits build up when the plug fails to fire correctly and burn them off. Air/fuel mixture too rich, choke stuck on, electrical problem, extended periods of low speed driving, plug heat range too cold.

[Baz]

Carbon deposits build up when the plug fails to fire correctly and burn them off. Air/fuel mixture too rich, choke stuck on, electrical problem, extended periods of low speed driving, plug heat range too cold.

All of the above but 10 miles is not enough distance to get a good reading. Do you have a faulty plug?

[John Luciano]

We changed plugs changed heat range to a hotter plug. they were thinking faulty ignighter , the coil was tested ok. Reason for the 10 miles is the bike almost doesn't make it back home from that distance . WE are talking 1 Soot black totally fouled plug. The other is perfect . If the ignighter (Brain ) is not working the plug would not fire at all. it must be firing to produce carbon

[Baz]

True, but it could be a very weak spark, regardless you are not getting good combustion. Try swapping the plugs around.Will it start as per normal? If it is sooty rather than wet it appears to me to be electrical rather than fueling.

[Gorilla]

I agree with Baz. Sounds like you are not getting enough voltage to completely fire the plug. Could be as simple as a bad plug wire, or as complex as a weak coil for that cylinder.

[tis]

Sounds like faulty plug wire. Running at night in dark can you see spark jumping?

[John Luciano]

We swapped plugs. We had it working for up to 60 miles then all of a sudden it started skipping. We are on the 3rd set of plugs. As stated before the coil was bench tested for 20 min. and had a big blue spark. I think it is something intermittent like a plug wire. The carb. has been gone thru the guy is a real good wrench not a fly by night . been working on Bikes for 20 years . Mostly Jap bikes .

I was thinking a sticking valve.

[tfdeputydawg]

:wtg::wtg:

Sounds like faulty plug wire. Running at night in dark can you see spark jumping?

[BlueTrinity]

I would check out that plug wire, John. At that age, it could easily be a crack you can't see, or even a break in the conductor cord.

First thing to do is check it for continuity with a multimeter. The resistance should be at zero ohms (but no more than 0.05). Anything else is a faulty wire.

Next best bet is to somehow get a fault code reading. If it is running that bad, there's a code in the ecm to give you some clues.

I'm betting on the bad wire, but Good luck!

[John Luciano]

It would answer the question of y it will run like a bear for a while and then all of a sudden be dead. He had it running for about 60 miles and then it started running on one cylinder. This all started when he drove it home in a downpour.

[skuuter]

Ride the Bike to a parking lot/driveway, shutting it off immediately under power, coasting it in (don't let it idle), then screw the plugs out and look at them. Easier to get true readings this way....

[Greydog]

A friend of mine had the same problem years ago with a Honda CB450. It would run great for 10 or 12 miles and then the right cylinder would shut down. Turned out to be a coil winding that was expanding and opening when the engine heated up. When cold the winding was conducting but producing a weak spark and fouling the plug. I'm sure the same thing could happen to a plug wire.

Also had a similar problem with one of my old bikes caused by the points being pitted but that's not an issue on later model bikes.

[John Luciano]

iT HAS GOT TO BE SOMETHING qUIRKY.. tHE INGNIGHTER OR COMPUTER CAN'T BE SCREWING WITH IT BECAUSE FROM MY EXPERIENCE WHEN THEY DI THEY ARE DEAD. THEY DONT WORK SOME TIME . Opps cap lock was on sorry .

[rog1215]

here is one for the books. I had done a complete top end on my 62 panhead.
ran the bike around town and always fouled out the rear plug.
Checked all the usual suspects and went as far as to pull the head off to check my valve job.
To make a long frustrating story short, it turned out to be the jett on my carburators accelerator pump was pointing right at that rear intake and everytime i gave it a goose it squirted way to much juice in that head,
this was a Bendix carb that i had rebuilt and set the pump setting to strong and as mentioned pointed in the wrong direction.
I fixed it but eventually went to the S&S which was a far superior carb.
Hope this helps.
Roger

[tudor29]

i had a 99 suzuki 1500 had the same problem it was the carbs that went bad 99-2000 bad years. seen 3 bikes in the shop with the same problems. cast alum. and stainless steel dont like each other

[John Luciano]

So where do I get a new carb? They bought new orifice . Where the pin fits in it was worn egg shaped . The carb was rebuilt by an experienced bike mechanic. this bike is a Suzuki 1500 2003. the carb has no pump it is a slide type.