One plug still fouling

Robdlouisville

Rob in Louisville, KY
Joined
Jun 13, 2012
Messages
25
Age
68
Location
Louisville, Kentucky
Bike
2000 St1100
Hello all:
Every 2000 miles one spark plug gets so fouled that the engine suddenly loses power, backfiring, etc. Friday all was well on the way home from work. At a red light, out of nowhere, the engine loses power, backfires all the way home. This has happened about every 2000 miles in the past year. I have only had it a year. I replaced the plug nearest my right knee (when I am seated on the bike). It is aways the same plug that is the culprit. So obviously that rear right cylinder is getting too much gas, not enough of something, too much of something. I do not know enough to tell. Would this be a carb sync issue? Also - this plug , when removed, smells of gasoline - the other 3 do not.

2000 ST1100. 35,500 miles

Thanks. - RD
 
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Most likely either a primary or secondary ignition issue. Rule of thumb is ignition before fuel with these issues. Way too many jump to things being fuel issue instead of ignition issues. This also holds true in the automotive world. Since plug smells of gas, definitely ignition issue......plug wire and connector at plug would be a good start.;)
 
Cylinder #3 you say.

My guess would be the vacuum shutoff valve developing a slight leak and allowing gas to enter #3 cylinder bit by bit in through the vacuum hose.

Julien
 
Did a search of the site and found this for firing order.

https://www.st-owners.com/forums/archive/index.php/t-40572.html

Found this too, at another site... just part of the wisdom there... about 1/2 way through might be the part you're looking for concerning just one cylinder. I bolded some stuff I thought relevant, and I always do the easiest stuff that it could be first. For instance, you're not parking under a rain gutter, or that cycinder getting the plug wire wet or something like that, or a bee or spider made a nest inside the spark plug wire, easy to arm chair troubleshoot! Good Luck!

IGNITION


No spark at all plugs (Faulty input system) If there is no spark at all plugs, the problem could be at the input of the ignition system


Possible system:

---pulse generator

---power input circuit of the spark unit

---neutral switch

---side stand switch---spark unit

---Check for loose or poorly connected spark unit connector.

---Check for loose or poorly connected ignition coil 3P mini connector.

---Check if battery voltage is measured between power input line (Black/White) and ground (Green) at the spark unit connector with the ignition switch ON and the engine stop switch at RUN

---Faulty ignition switch or engine stop switch

---Open circuit in wire harness

---Loose or poor contact of related circuit connectors

---Faulty bank angle sensor relay

---Faulty bank angle sensor

---Measure the pulse generator resistance at the spark unit connector

---Check the neutral switch for continuity at the spark unit connector

Alternator

---Open circuit between the unit and pulse generator

---Loose or poor contact of the pulse generator connector

---Check the neutral switch.

Faulty neutral switch

---Open circuit between the unit and neutral switch

---Loose or poor contact of the neutral switch connectors

---Faulty spark unit

Faulty side stand switch

---Open circuit between the unit and side stand switch

---Loose or poor contact of the side stand switch connector


No spark at either ignition group

---If there is no spark at either group, the problem is suspected in the primary coil side of the ignition system ignition coil, or unit and ignition coil circuit.

Switch the ignition coil primary terminal connection between the faulty pair and the good pair

Try spark test again, if "No Spark" condition: shifts to other pair

Measure resistance of the ignition primary coil at spark unit connector.

---Remove the faulty pair ignition coil and check pair.

---No Spark condition remains with faulty pair

---Faulty ignition coil

---Faulty spark plug wire

---Poor or loose contact of ignition coil SF mini connector

---Open circuit between the unit and ignition coil

---Faulty spark unit

---No spark at one plug (Trouble in secondary coil side)

---Faulty spark plug is most likely.

Replace (suspected bad spark plug) with known good spark plug and conduct spark test.

---Original spark plug no good.

---Put the spark plug wire on and measure resistance of ignition secondary coil.

Remove the spark plug wire, and measure the resistance of the ignition secondary coil.---Conduct spark test on good ignition coil.

Faulty ignition coil

---Poor contact of spark plug wire

---Faulty spark plug wire

Side stand switch does not function at all.

Side Stand Indicator:

---Check the side stand indicator for function.

Side Stand Switch:

---Check the side stand switch for continuity.

---Faulty side stand switch

---Open circuit in Green/White or Green wire

---Loose or poor contact of related connectors

---Open or short circuit in wire harness

---Burnt indicator bulb

---faulty side stand switch
 
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mikew1231 said:
Did a search of the site and found this for firing order.

https://www.st-owners.com/forums/archive/index.php/t-40572.html

Found this too, at another site... just part of the wisdom there... about 1/2 way through might be the part you're looking for concerning just one cylinder. I bolded some stuff I thought relevant, and I always do the easiest stuff that it could be first. For instance, you're not parking under a rain gutter, or that cycinder getting the plug wire wet or something like that, or a bee or spider made a nest inside the spark plug wire, easy to arm chair troubleshoot! Good Luck!

IGNITION


No spark at all plugs (Faulty input system) If there is no spark at all plugs, the problem could be at the input of the ignition system


Possible system:

---pulse generator

---power input circuit of the spark unit

---neutral switch

---side stand switch---spark unit

---Check for loose or poorly connected spark unit connector.

---Check for loose or poorly connected ignition coil 3P mini connector.

---Check if battery voltage is measured between power input line (Black/White) and ground (Green) at the spark unit connector with the ignition switch ON and the engine stop switch at RUN

---Faulty ignition switch or engine stop switch

---Open circuit in wire harness

---Loose or poor contact of related circuit connectors

---Faulty bank angle sensor relay

---Faulty bank angle sensor

---Measure the pulse generator resistance at the spark unit connector

---Check the neutral switch for continuity at the spark unit connector

Alternator

---Open circuit between the unit and pulse generator

---Loose or poor contact of the pulse generator connector

---Check the neutral switch.

Faulty neutral switch

---Open circuit between the unit and neutral switch

---Loose or poor contact of the neutral switch connectors

---Faulty spark unit

Faulty side stand switch

---Open circuit between the unit and side stand switch

---Loose or poor contact of the side stand switch connector


No spark at either ignition group

---If there is no spark at either group, the problem is suspected in the primary coil side of the ignition system ignition coil, or unit and ignition coil circuit.

Switch the ignition coil primary terminal connection between the faulty pair and the good pair

Try spark test again, if "No Spark" condition: shifts to other pair

Measure resistance of the ignition primary coil at spark unit connector.

---Remove the faulty pair ignition coil and check pair.

---No Spark condition remains with faulty pair

---Faulty ignition coil

---Faulty spark plug wire

---Poor or loose contact of ignition coil SF mini connector

---Open circuit between the unit and ignition coil

---Faulty spark unit

---No spark at one plug (Trouble in secondary coil side)

---Faulty spark plug is most likely.

Replace (suspected bad spark plug) with known good spark plug and conduct spark test.

---Original spark plug no good.

---Put the spark plug wire on and measure resistance of ignition secondary coil.

Remove the spark plug wire, and measure the resistance of the ignition secondary coil.---Conduct spark test on good ignition coil.

Faulty ignition coil

---Poor contact of spark plug wire

---Faulty spark plug wire

Side stand switch does not function at all.

Side Stand Indicator:

---Check the side stand indicator for function.

Side Stand Switch:

---Check the side stand switch for continuity.

---Faulty side stand switch

---Open circuit in Green/White or Green wire

---Loose or poor contact of related connectors

---Open or short circuit in wire harness

---Burnt indicator bulb

---faulty side stand switch
Click to expand...

Faulty coil suspect ONLY if both 3-2 cyl. not firing or both 4-1 not firing. Swapping the pairs would verify that.;)
 
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Thanks to everyone for responding. I think I will replace wires and check into the vacuum leaks possibility. Will let you all know how it goes. The one issue that confuses me is....why all of a sudden? One day I'm driving fine and at a red light - boom - starts running rough and no power. Almost like it sucked in poisonous gasoline or something, that quick.....RD
 
Robdlouisville said:
Thanks to everyone for responding. I think I will replace wires and check into the vacuum leaks possibility. Will let you all know how it goes. The one issue that confuses me is....why all of a sudden? One day I'm driving fine and at a red light - boom - starts running rough and no power. Almost like it sucked in poisonous gasoline or something, that quick.....RD
Click to expand...

Fine one minute, bad the next is also consistent with an ignition wire/plug cap failure. If you're getting a misfire at certain RPMs, or engine loads, that's also something that you get with an ignition failure. An ignition scope is good for diagnosing this type of thing if you can get access to one for free or for a small charge.
 
I wonder if you could see a bad boot by looking at the bike while running in the dark. Might be able to see a small amount of light, I've seen it before on cars. And Brant is correct on the coils, 2 cylinders wouldn't fire if it was a coil. I checked the Honda service manual and it has 2 different heat range of spark plugs that you can use. One for normal driving (CR8EH 9) and one for extended high speed driving (CR9EH 9). If I were you, the cheapest thing to do would be to simply switch 2 spark plugs and see if the problem changes to another cylinder. A friend of mine at work takes his old plugs and boils them in water, I've never tried it, but he seems to think that it cleans the plugs really good. I would read Dinky's posts too, and really look at that boot close, at least take it off and give it a good visual. The posts mentioned tell how to do this. You'll fix this! Just do it!
 
Correction:

I didn't realize you were working on an 1100 before I responded. I don't know anything about them. I was referencing the 1300 which can certainly have spark plug boot problems. A carbureted engine leaves another possibility to look for. Good luck!
 
Basically 2 things will cause a fuel flooded spark plug. Weak fire to that plug or a rich fuel system. A weak coil can be ruled out since the other plug fired by that coil is fine. that leaves a bad plug wire for the fouled plug, but I might rule that out since that cylinder takes 2000 miles to foul. . A leaking carb boot would run lean, not rich. I would guess either a float that is not floating high enough causing too high a fuel level or the needle and seat is leaking. 3rd choice would be the cold start enrichment valve on that carb is leaking fuel (easiest to check).

To check the fuel level is high in one carb without tearing into the carb........drain all four carbs one at a time into a measured vial. All should measure roughly the same volume. If one has more fuel than the other 3, BINGO you have found the problem.
 
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Rossi may be on to something ..... re-read his post. That sounds like a logical possibility. But if not, then :

I would also do a compression test on all four cylinders. If they all look good, then I would swap the coils & spark plug wires from side -to-side to see if that same plug continues to foul or if another one starts to foul. If another plug starts to foul ( on the opposite side of the engine, then it's the coil or spark plug wire or spark plug connector. Gotta do some logical troubleshooting.
 
Re: One plug still fouling - how to change the boot and leave the wire

I should have switched the wires, but I already purchased a new boot for the #3 cylinder. The thing is - these are the originals or at least they look it. It appears on my bike that the wire and boot are all one. Can I separate them without destroying the wire? Do they just separate with pulling? Thank You - RD
 
Plug fouling - how to replace boot and not destry wire

Continued from first "plug still fouling thread". I purchased a new boot for the wire to the #3 cylinder. The thing is - these are the original wires or at least they look it. It appears on my bike that the wire and boot are all one. Can I separate them without destroying the wire? Do they just separate with pulling? Thank You - RD
 
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