S3 keeps fouling right side spark plug

[s3a]

Hi all,

I have a 1975 S3 , i've been having a spark plug fouling issue for a while now, only on the right side cylinder. It will start and run ok from cold , idles fine on all 3, but as soon as i get out on the road and put a load on the engine it starts to foul the right side spark plug only (others are a nice beer bottle brown color). This bike ran very good for years on the current jetting/filter/pipe combo. I did alot of work to the bike this winter that was well needed, thinking somewhere along the way this issue would be resolved. Here is a list of things I have done, with no luck solving this issue:

-Crank rebuild,new bearings and seals
-Fresh top end, .5 overbore, good compression all 3
-Real good carb cleaning and inspection, viton tip float needles and reset float heights
-New choke plungers, sync'd
-Throttle cables sync'd
-New Nippon Denso points and condensers, timed with multi meter set to beep
-All new ignition coils
-New copper core wires and non resistor caps, NGK b8hs plugs gapped to .026
-Petcock rebuilt, new fuel line and filters
-Brand new yuasa 12n5.5 battery


There are no fuel leaks from the petcock or the carburetors, and the spark looks very bright on all 3 plugs visually when kicked over. Last year I tried swapping the center and right side carbs with no change (which made me think it was weak spark). The exhaust pipes are free and clear, all breath well. I will also mention that this bike has been running premix for a long time now, the oil pump and lines are deleted, so it's not an "over-oiling" issue. This really has me stumped , just wondering if anyone has experienced anything like this before

[shiloh]

The most common reasons for a plug to foul are dirty air filter(s), weak spark(ignition), or an overly rich condition(carb).

Only guessing here but maybe your right carb is too rich. I run temp gauges on all three carbs to monitor carb settings, an overly rich carb will run a cylinder colder than whats needed to keep the plug from running at optimum temp to prevent fouling.

You could check that and maybe try a hotter plug.

[Curtis]

Shut the bike off and lean the bike over to the right and see if fuel comes out the overflow
Needle and seat not sealing properly/at all will cause fouling

Is it carbon fouling or gas fouling ? (Dry and super black or wet and super black?)

[zambia]

The S3 is one of the only bikes that will allow you to put a slide in backwards. I would be almost certain this is your issue. Super easy to figure out - just take off your filter or inlet tubes and put your little fingers against the slides - if the right cylinder feels like a different shape cut out...the slide is backwards. And yes, I know from experience - amazingly, this kills a plug DEAD never to spark again!

[s3a]

Thanks for the input guys, as far as the carb being richer than the rest , they have the same jetting and same filter right across the board. Jetting is as follows:
22.5 pilot, air screws set around 1 3/4
#95 mains
Stock 4ej4 needles on the 4th clip
Viton tip float needles, float heights set to 25.5 - 26mm
Uni foam filters

The plugs are gas fouling, they don't even have a chance to turn black before they are soaked

I have mistakenly put a slide in backwards before haha, but this time it's not the culprit, that was one of the first things I looked at last year

[Curtis]

Your needle is not sealing then.

[s3a]

Recent picture of the bike just for good measure


I have filled the carb with gas while off the bike , lightly clamped in the vice at the same angle as it sits on the bike, and the needle and seat will shut the fuel off without over flowing. Maybe I should try pressure testing it

[mraxl]

It needs to be established whether it is a spark or fuel issue.
Even though you have swapped carbs earlier I would do it again (with cables, slide, filter, etc included).

[s3a]

Thanks mraxl, I'll try swapping them again and see if the problem moves

[acceleration]

Have a good look at your petcock.Gas valve.When the seals wear out.It does NOT shut off. Fuel leaks by.The carbs fill continually,The fuel flow does not stop.The fuel level in the float bowls gets too high.Causing a rich condition.If the leak is really bad it will leak out the carbs and puddle on top of the engine.Pull one or two of the fuel lines off the carb.And see if it drips ? I have had and seen a similar problem you are having.And that was the cause Of course there could be a number of causes and it is a process of elimination.This just a "suggestion" among other things to try.If it is just happening on ONE cylinder it might be something else ? If it is only on one cylinder switch the carb and coil with one of the others ? But try coil or carb one at a time.Not both at once.

[Curtis]

If a needle and seat in the carb is functioning correctly you do not even require a fuel cock.....

[Johnny O]

Check to make sure your choke cable has slack in it and your choke is not pulled ..

[acceleration]

Bad petcock has the same effect as leaving the lever on the constant run IE: steady flow.Leave it on run for an experiment for a couple of days and see what happens, with steady fuel flow ? See if the carbs don't over flow ?

[s3a]

I haven't had time to try switching the carbs yet, but I had pulled the fuel lines off the carbs the other day and today I noticed they are dripping a bit with the petcock "off". This is a bit of a piss-off considering I just put a rebuild kit in it this winter, maybe it is worn beyond repair. What are you guys doing with the baby triple petcocks these days ? New Chinese ones any good ?

[acceleration]

Several years ago.I went to start my 500 and it was flooded.It wouldn't start.I saw some fuel on the floor and on top of the engine cases.So I figured the needle seats were bad.I pulled all three carbs.I rebuilt them put in new needle seats then fired up the bike and it was fine and running well.Took it out for a ride and was a happy camper again.Parked the bike.Came back to start it again a few days later and SAME thing happening !! Bike flooded.Fuel on floor and on top of the engine cases !! I checked the petcock fuel valve and it wasn't shutting off fuel leaking past.Pressure from the constant fuel flow pushing past the needle seats.I rebuilt the carbs for nothing !! LOL !! I got one of those petcock rebuild kits and it fixed the problem. But the problem came back and the bike flooded again after a couple of months.I finally went and bought a new four hole rubber seal directly from Kawasaki and installed it and the problem never came back.I guess the ones in the aftermarket kits aren't as good ? Get the four hole gasket directly from Kawasaki if still available ?
Take some fine sand paper and on a piece of glass and clean up the flat surface of the control for the positioning of the valve, to make sure it is clean and flat, and try the OEM four hole rubber seal.Not100% sure if that is what is causing your over all problem?Just a suggestion. But that is what happened to me.And what I did to fix the flooding over rich problem I had.