Cylinder # 3 spark plug fowled despite no vacuum valve.

[Christianncg]

Well, This thread still isn't solved. After replacing the float needles and seats, setting float height to 7mm using the method outlined in st-riders and idling for 5 mins with new spark plugs I was greeted with Cyl. 3 still being black, Cyl. 1 being dark brown, and Cyl. 4 and 2 being nigh clean still with some touches of brown appearing. No Choke was applied, the idle was adjusted at 1200 cold for testing purposes. I have same colored spark (I will be buying a spark plug tester later today), there were no holes in the diaphragm for the carb slide (although was a bit sticky.) Last time I checked the air cutoff valves were fine, but will probably be checked again.

Soo

1. Either my coil is bad, not bad enough to drop a cylinder but enough to miss and soot a plug..

2. Some how, excess fuel is getting past the new needles and seats despite having appropriate flow on the pump, the slow jets at 40# and the screw turns at 1 7/8 for each cylinder, compression at 165 all around each cyl. I noticed raw fuel on Cyl. Number 3 plug where the others did not have, and Cyl. Number 1 was heading the way of its brother. Sync is good, none of the throttle plates look out of whack compared to the others... Air cut off looks good.

3. At higher RPMS and idle, a translucent cloud of white smoke can be seen puffing on every occasional miss at idle.

I'm at a loss. I'll be shotgunning some parts here real soon.

 

[dwalby]

I remember you initially had a bad plug cap on #3, and claimed to have fixed it, any chance that's still a problem? "every occasional miss at idle" sounds like a possible ignition issue, does it miss at high RPM too, that part wasn't clear. If its missing at certain RPMs consistently, that's very likely an ignition problem.

 

[Christianncg]

Well, miss is a strong way to put it. more like a burble. It revs really, really cleanly which is confusing to me because bikes that miss sound like garbage when revving and holding a certain RPM. . . I've pulled a plug before and the bike wont run. I ran an spark tester and seem to get the same jump between all cyl.. Was expecting the coil on the right bank to be weak.

 

[bdalameda]

A carb badly out of synch perhaps or the enrichener (choke) circuit not shutting off and allowing excess fuel into this cylinder.. Would not be the first time I have seen the choke linkage not allow the enrichener plunger to fully seat.

 

[Christianncg]

I've tested both of those theories and came up nill. The sync has been verified a few time now as I do it every time the carbs come off. The enricher plunger is seating correctly as well. However I now suspect that maybe an air jet is clogged somewhere, and that I missed cleaning it due to the carbs being ganged and not seeing it in the air cut off valve. I'm going to give an all day cleaning session in a few days along with swapping the coils and cleaning the plugs. Theres gotta be a reason for this.

 

[bdalameda]

Even if the enricher is seated the seal at the bottom of the plunger may be bad and allowing fuel to bypass the seal.

 

[Christianncg]

Even if the enricher is seated the seal at the bottom of the plunger may be bad and allowing fuel to bypass the seal.

I noticed that if I squished #3's enrichening plunger, the seal was squishy, and would move a little bit. Its not far fetched to believe that fuel could be seeping from that orfice.... I feel like your on to something. I will check when I get home.

 

[Christianncg]

Case closed. Thanks bdalameda. Bike no longer dumps fuel in the cylinder, and all plugs look clean after a 30 min trip around the block. The solution was probably a combination of things:

1. Cleaned all the air jets, and the entire pilot circuits of the carb. Nothing seemed obstructed and nothing came out of any passages

2. Removed the rubber seal for the enricher plunger which had a ring from the sealing edge on the carbs, as well as a bit of hardness. Took a pick, pried at the edge of the rubber, got it out and turned it around on all of the carbs. A bit difficult, but the back side of the seal was nice and supple, with no indentations to be seen. This was probably the culprit.

3. Swapped coils. Kinda useless at this point but if the dark plugs come back on the opposite side I will know it's coil replacement time.

4. Set all floats to 7mm, to correct the 8mm I did for the giggles. To be clear, this was a compounded problem. I think the float needles were bad, allowing dumping of gas on number 3, AND the enricher plunger seals were all crispy, particularly number 3, causing a rich condition after the float needles were installed. I probably disturbed the plunger when I did the float needle replacement.

Bike runs cleaner now, if there ever was such a thing. More snappy, thanks to those 40 slow jets hauling raw booty in the lowend. Front tire attempted to ascend to the heavens but was not worthy. Now, to wire up my GPS and 12v outlet for TentSTOC. So excited!

 

[TerryS]

Case closed. Thanks bdalameda. Bike no longer dumps fuel in the cylinder, and all plugs look clean after a 30 min trip around the block. The solution was probably a combination of things:

1. Cleaned all the air jets, and the entire pilot circuits of the carb. Nothing seemed obstructed and nothing came out of any passages

2. Removed the rubber seal for the enricher plunger which had a ring from the sealing edge on the carbs, as well as a bit of hardness. Took a pick, pried at the edge of the rubber, got it out and turned it around on all of the carbs. A bit difficult, but the back side of the seal was nice and supple, with no indentations to be seen. This was probably the culprit.

3. Swapped coils. Kinda useless at this point but if the dark plugs come back on the opposite side I will know it's coil replacement time.

4. Set all floats to 7mm, to correct the 8mm I did for the giggles. To be clear, this was a compounded problem. I think the float needles were bad, allowing dumping of gas on number 3, AND the enricher plunger seals were all crispy, particularly number 3, causing a rich condition after the float needles were installed. I probably disturbed the plunger when I did the float needle replacement.

Bike runs cleaner now, if there ever was such a thing. More snappy, thanks to those 40 slow jets hauling raw booty in the lowend. Front tire attempted to ascend to the heavens but was not worthy. Now, to wire up my GPS and 12v outlet for TentSTOC. So excited!

Good work Christian, and thanks for posting this. It would be great if there was a post-script after a week or so of riding. My bike exhibits a similar apparent richness on #3 and I too have cleaned the carbs (too many times), replaced the air filter, replaced the carb rubbers, set the floats, changed the air-cut rubbers, and replaced the plugs, plug caps and leads, but nothing really changed the appearance of that plug. I have looked at the chokes but only to ensure they all visually closed plus some slack when the lever is off.

 

[dwalby]

My bike exhibits a similar apparent richness on #3 and I too have cleaned the carbs (too many times), replaced the air filter, replaced the carb rubbers, set the floats, changed the air-cut rubbers, and replaced the plugs, plug caps and leads, but nothing really changed the appearance of that plug. I have looked at the chokes but only to ensure they all visually closed plus some slack when the lever is off.

probably a dumb question, but you didn't mention if you've already removed the vacuum shutoff valve, I assume you have.

 

[Christianncg]

Good work Christian, and thanks for posting this. It would be great if there was a post-script after a week or so of riding. My bike exhibits a similar apparent richness on #3 and I too have cleaned the carbs (too many times), replaced the air filter, replaced the carb rubbers, set the floats, changed the air-cut rubbers, and replaced the plugs, plug caps and leads, but nothing really changed the appearance of that plug. I have looked at the chokes but only to ensure they all visually closed plus some slack when the lever is off.

I would inspect the enrichener plug for any rings around the rubber seal for the plunger. Mine looked fine, but was seeping fuel around the seal, probably from mixing the plungers around while polishing the brass tidbits. There is also coils too, as well as idle settings. Mine were all at 2 turns for the #40 slow jet. If your float needles and seat are original, and have any distinguishable lines in the needle tip (polished spots) get new ones, either K&L 18-4738 or Honda OEM. I would recommend replacing the enrichment plunger if any problems are found. Removing the rubber seals without damaging them is difficult.

Vacuum valve too, but I assumed you already removed that, everyone seems to have pulled theirs on this forum. Mine came without one.

 

[TerryS]

I would inspect the enrichener plug for any rings around the rubber seal for the plunger. Mine looked fine, but was seeping fuel around the seal, probably from mixing the plungers around while polishing the brass tidbits. There is also coils too, as well as idle settings. Mine were all at 2 turns for the #40 slow jet. If your float needles and seat are original, and have any distinguishable lines in the needle tip (polished spots) get new ones, either K&L 18-4738 or Honda OEM. I would recommend replacing the enrichment plunger if any problems are found. Removing the rubber seals without damaging them is difficult.

Vacuum valve too, but I assumed you already removed that, everyone seems to have pulled theirs on this forum. Mine came without one.

Yes I already replaced the float valves as well (so many changes I forgot that one) and I have the pilot screws at 1 7/8 at present but will drop to 1 5/8 soon as my idle drops when I stop which is a rich symptom. Vacuum valve is long gone too.


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[Christianncg]

Yes I already replaced the float valves as well (so many changes I forgot that one) and I have the pilot screws at 1 7/8 at present but will drop to 1 5/8 soon as my idle drops when I stop which is a rich symptom. Vacuum valve is long gone too.


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another thing that comes to mind... Is your fuel pump factory or aftermarket? Compression ok in that cylinder?

 

[TerryS]

another thing that comes to mind... Is your fuel pump factory or aftermarket? Compression ok in that cylinder?

Factory pump, I did have an Airtex in there for a while but thought I'd try an OEM and see if it made any difference (nope) and logically, why would it? The fuel level in the carbs is controlled by the floats so unless the alternative pump produced pressure enough to overcome the float valve seals, the fuel level and flow through the carbs is unchanged.

I've never checked the compression, I bought the bike cheap as a non-runner that had been parked up (but not stored) for 10 years and the tank, original pump, filter and carbs were predictably tragic. It is possible that there could be some reason for low compression (ring damage? valve seat damage?) but the bike runs great and the valve clearances were all spot-on and have been stable over 30,000km so I don't have any reason to suspect that.

 

[Christianncg]

Sorry for the late reply. I had a loss of power on the bike after installing a gps adapter plug. Blew no fuses, neither main nor any sub fuses, even had power at every endpoint. For some reason the voltmeter I installed was causing ground to float up to battery positive, seeing positive voltage at every negative point on the bike. Which is weird. I know about floating grounds but never on a motorcycle. Just Tube radios.

That being said, I am at a loss for now so I'll just describe everything I can think of off the top of my head then go to bed, because working on a bike in an oven for a garage is hell.

1. Needle play? Is the jet needle for the CV slide in place correctly? A wiggly or too high up jet needle will cause issues. There will be some play under the small spring tension of the retainer.

2. Sticking CV slide. Do the slides drop down successfully on their own, without spring pressure? (clunk test). If not it may be wise to inspect them for scoring around the slide bore.

3. Plunger leaking fuel, mentioned earlier.

4. Slow air jet and main air jet (the orifices around the circumference of the snorkels) are blocked or restricted still despite cleanings. These jets reduce vacuum to the slow and main jets, reducing fuel draw. When plugged you will get black spark plugs.

5. Air cut off valve is stuck closed (unlikely.)

6. Plugged carb vent lines.

7. Float needle is still seeping gas., or float is taking on gas internally. You can test this by removing the carbs, setting them on a stand near the right side of the bike, and either jumping the fuel pump positive wire to battery (do at your own risk), or just priming the fuel pump with a few key turns every couple of seconds. Floats that take on gas will seep air every moment or two if set in a cup of gas. d

8. A small gremlin that crawls from the depths of hell and fondles your idle mixture screws at night.

9. A weak ignition system, either coil voltage or windings. ( Whats the ohms on the secondary windings? The primary?

There. I think that's it. Time for a beer.

 

[ST Gui]

10. Remove poultry from cylinders?

 

[TerryS]

Sorry for the late reply. I had a loss of power on the bike after installing a gps adapter plug. Blew no fuses, neither main nor any sub fuses, even had power at every endpoint. For some reason the voltmeter I installed was causing ground to float up to battery positive, seeing positive voltage at every negative point on the bike. Which is weird. I know about floating grounds but never on a motorcycle. Just Tube radios.

That being said, I am at a loss for now so I'll just describe everything I can think of off the top of my head then go to bed, because working on a bike in an oven for a garage is hell.

1. Needle play? Is the jet needle for the CV slide in place correctly? A wiggly or too high up jet needle will cause issues. There will be some play under the small spring tension of the retainer.

2. Sticking CV slide. Do the slides drop down successfully on their own, without spring pressure? (clunk test). If not it may be wise to inspect them for scoring around the slide bore.

3. Plunger leaking fuel, mentioned earlier.

4. Slow air jet and main air jet (the orifices around the circumference of the snorkels) are blocked or restricted still despite cleanings. These jets reduce vacuum to the slow and main jets, reducing fuel draw. When plugged you will get black spark plugs.

5. Air cut off valve is stuck closed (unlikely.)

6. Plugged carb vent lines.

7. Float needle is still seeping gas., or float is taking on gas internally. You can test this by removing the carbs, setting them on a stand near the right side of the bike, and either jumping the fuel pump positive wire to battery (do at your own risk), or just priming the fuel pump with a few key turns every couple of seconds. Floats that take on gas will seep air every moment or two if set in a cup of gas. d

8. A small gremlin that crawls from the depths of hell and fondles your idle mixture screws at night.

9. A weak ignition system, either coil voltage or windings. ( Whats the ohms on the secondary windings? The primary?

There. I think that's it. Time for a beer.

Thanks for a very detailed response. You've earned that beer. I have checked most of your list off, certainly the slides move freely, the floats float, the carbs vent, all the jets/vents are clear (as I cleaned my carbs 6 times chasing a fault that was actually electrical in nature), and the ignition system is (now) very healthy.

Aside from the choke plungers, my other suspicion was wear in the emulsion tubes (the fixed orifice in the carb floor that the needle enters) as by eye these do look a little oval. A previous bike (Suzuki RF900R) was notorious for wear here, and after 30,000km on that my fuel consumption was through the roof and plugs would regularly foul. These were an easily replaced part and my tank range went from under 200 to over 300km with that simple fix. On the ST carbs I don't think these can be replaced.

 

[Christianncg]

The beer was particularly good, thanks. Four peaks is the one thing good about Arizona. You would be the first to complain of ovaling needle jets on this bike. It would be nice if someone was near by to compare specifications with you to confirm your worries.

 

[Christianncg]

So, to close the book on this thread, my bike is still fine after 300 miles or so. Plugs look nice and cookie like. No issues to be found.

 

[2000st1100az]

I'm in the beginning stages of the exact same battle. We shall see were I end up. Lol