Left side plugs carboned up

[Edster]

Yesterday i inspected my plugs to find the right side looked perfect and the two left side looked oily with carbon deposits. I sense a pattern here that could be due to ignition performance/coils etc. Anyone ever seen this before? I have been running it fairly low rpm for the last six months of commuting in sometimes very slow traffic. I also know the last owner did some wiring update to bypass something in the electrical circuit brittle wiring on Sts around the stator or something to that effect. The bike was running kind of rough below 2200 rpm but seemed to run fine after fully warmed up or at higher RPMs. Gets around 40mpg here with crappy TX ethanol fuel. I recognize this is not much help but thought I'd toss it out...

thx

 

[mcthorogood]

It could be that your carburetors need to be synchronized. LINKY

 

[bdalameda]

Carb synch or the choke enrichener is not closing all the way on that side. Float level or dirty float needle seats also possible. Ignition won't cause buildup if the engine is running on all cylinders. Spark does not control heat range - heat range and plug cleanliness is determined by fuel mixture and plug insulator temperature, not the spark itself.

Dan

 

[Brant]

Your carbs are having secondary ignition issues.

 

[dwalby]

The fact that you are seeing an issue with two cylinders, which I believe are linked to a common ignition coil (not at home, can't check the manual to make sure) certainly makes ignition a suspect. With 4 individual carbs, its not likely that two carbs would simultaneously have exactly the same problems, but I wouldn't say its impossible, just not very likely. Carb sync likely has nothing to do with it, it doesn't have enough of an effect to control mixture to that extent. Editorial note: I've always believed that carb sync is a joke, I've never seen it make any difference on any bike I've owned, and haven't carb synched my ST in 10 years with no ill effects. Others here will disagree with my opinion and claim it affects everything from engine smoothness to MPG.

I haven't tried it, but I would assume its not too difficult to swap the two ignition coils around and see if the symptom shifts to the other side. Costs nothing to try except your time, and if the symptom follows the coil you have a reliable diagnosis. I'm certainly no expert, but I believe that sooty plug residue is consistent with weak ignition spark, but I could be wrong, I don't have a lot of experience with poor running bikes.

 

[Jim Van]

I haven't tried it, but I would assume its not too difficult to swap the two ignition coils around and see if the symptom shifts to the other side. Costs nothing to try except your time, and if the symptom follows the coil you have a reliable diagnosis. I'm certainly no expert, but I believe that sooty plug residue is consistent with weak ignition spark, but I could be wrong, I don't have a lot of experience with poor running bikes.

+1 on the above , but I would first check to see if the carb choke linkage is somehow malfunctioning and keeping the choke from opening completely on the two left carbs. That would be doing the easy thing first.

 

[dwalby]

I yanked the carbs to do my hose changes, but never paid any attention to the choke linkage other than disconnecting the main cable. Do those things operate in pairs?