lloyd54123
Member
Hey I'm new to the forum and pwc. I rebuilt a 93 seadoo spi and had these plugs in for about 2 hours and they are just barely brown. Is that long enough to know if I'm running lean? If so would that contribute to a starting issue? 
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Running lean?
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Sportster-2001-951C-Stock
Well-Known Member
A few thoughts, loosely presented..... You'll have to provide some more detail of course!
Although those are approaching rather grey as opposed to brown they might be acceptable, depending.
One is distant, harder to see and looks almost silver (aluminum?).
It's harder to judge plugs after idling too long (more than a few minutes) due to fuel soot grows on cold plugs.
Are you using Seadoo oil or some other brand and more importantly, has the engine been hesitating or lean-surging?
My plugs do tend to run closer to grey when I operate at lower speeds such as with a water skier who's learning and has yet to get up his first time. Plugs run colder then, and don't reach temps high enough to self-clean thus fuel soot becomes part of the normal brown oil coloring.
Otherwise, a new set of plugs will take on a yellow insulator color during the first ~20 minutes of riding across the lake on plane at a normal clip, and eventually after 30 minutes begin settling to chocolate brown.
Hard starting can be caused by several things, generally too rich or lean while hot or cold. If applying choke during cranking helps then probably the idle speed mixture is a bit lean and vice-versa.
If you must apply full throttle to clear a flooded condition while extended cranking warm then it's possible your fuel metering needle isn't seating properly, this condition will allow fuel to dribble down into your intake and puddle during shut down.
A weak battery can be the cause of hard starting, when voltage drops too low while cranking for the CDI ignition.
For this photo here, I rode across the lake at normal speed and approached dock at low speed maybe idled no more than a minute or two. These plugs had been in this engine for more than a few tanks of fuel, but I was curious.
Although those are approaching rather grey as opposed to brown they might be acceptable, depending.
One is distant, harder to see and looks almost silver (aluminum?).
It's harder to judge plugs after idling too long (more than a few minutes) due to fuel soot grows on cold plugs.
Are you using Seadoo oil or some other brand and more importantly, has the engine been hesitating or lean-surging?
My plugs do tend to run closer to grey when I operate at lower speeds such as with a water skier who's learning and has yet to get up his first time. Plugs run colder then, and don't reach temps high enough to self-clean thus fuel soot becomes part of the normal brown oil coloring.
Otherwise, a new set of plugs will take on a yellow insulator color during the first ~20 minutes of riding across the lake on plane at a normal clip, and eventually after 30 minutes begin settling to chocolate brown.
Hard starting can be caused by several things, generally too rich or lean while hot or cold. If applying choke during cranking helps then probably the idle speed mixture is a bit lean and vice-versa.
If you must apply full throttle to clear a flooded condition while extended cranking warm then it's possible your fuel metering needle isn't seating properly, this condition will allow fuel to dribble down into your intake and puddle during shut down.
A weak battery can be the cause of hard starting, when voltage drops too low while cranking for the CDI ignition.
For this photo here, I rode across the lake at normal speed and approached dock at low speed maybe idled no more than a minute or two. These plugs had been in this engine for more than a few tanks of fuel, but I was curious.
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lloyd54123
Member
Both plugs are about the same. Little grey and light brown. Xps mineral oil for 2 stroke. I was riding hard for a good half hour 45 min with a few breaks of slow speed. I needed to keep my idle pretty high for a while. As far as starting I would have to play with the choke and often had more success with the throttle. I'll try and bring the idle down and see how it starts. What should a battery be at while starting?
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Sportster-2001-951C-Stock
Well-Known Member
If while riding there's no lean stalling, hesitation or lean-surging then you might be okay. These are the big warning signs before a piston is melted. 2-strokes aren't forgiving of lean air:fuel mixture and carburetor passages become restrictive as they age.
XPS should result in brown color, I'd expect. Recently XPS color was changed from clear to red and I don't have the new red oil yet but it should make the same plug color due to the metallic lubricant package.
If you need to keep idle high, is this because of some running problem or personal choice? Carburetor issues?
FWIW, On trailer my Rotax 951 idles about 3500~3600 and in water about 1600, I like high(er) idle speed settings myself.
Idle speed shouldn't make major difference in warm restarting though. But idle mixture adjustment will make hard restarting. Idle mixture must be final adjusted in water for perfection of course. Usually factory spec idle mixture screw position is very close to perfect.
Anyway,
If idle mixture is too lean this means there's not enough fuel vapor trapped in crankcase from shutdown to make an easy warm restart first try. If idle mixture is too rich, this leaves excess fuel trapped in crankcase at shutdown then you must hold throttle open while warm cranking to finally get enough air.
Idle mixture setting is a balance.
Other stuff:
Also, hard starting in water can be caused by low cylinder compression (with new rebuilt that should be good though).
A good battery should make 11V during cranking engine.
If you have lean surge and hesitation issues, it's too lean and piston damage will happen. Carburetor internal filter, small passages are plugged maybe dirt and often corrosion of aluminum passages. Must clean thoroughly, sometimes that doesn't work so replacement with new carburetor is a good solution.
XPS should result in brown color, I'd expect. Recently XPS color was changed from clear to red and I don't have the new red oil yet but it should make the same plug color due to the metallic lubricant package.
If you need to keep idle high, is this because of some running problem or personal choice? Carburetor issues?
FWIW, On trailer my Rotax 951 idles about 3500~3600 and in water about 1600, I like high(er) idle speed settings myself.
Idle speed shouldn't make major difference in warm restarting though. But idle mixture adjustment will make hard restarting. Idle mixture must be final adjusted in water for perfection of course. Usually factory spec idle mixture screw position is very close to perfect.
Anyway,
If idle mixture is too lean this means there's not enough fuel vapor trapped in crankcase from shutdown to make an easy warm restart first try. If idle mixture is too rich, this leaves excess fuel trapped in crankcase at shutdown then you must hold throttle open while warm cranking to finally get enough air.
Idle mixture setting is a balance.
Other stuff:
Also, hard starting in water can be caused by low cylinder compression (with new rebuilt that should be good though).
A good battery should make 11V during cranking engine.
If you have lean surge and hesitation issues, it's too lean and piston damage will happen. Carburetor internal filter, small passages are plugged maybe dirt and often corrosion of aluminum passages. Must clean thoroughly, sometimes that doesn't work so replacement with new carburetor is a good solution.
lloyd54123
Member
Right after my build it would die at idle so I set it higher. I've since cleaned the carb and filters. Still need to check the fuel selector. I don't think I'm surging. I had an issue with it dying or losing power when I pulled the throttle to fast but that was when I was down to a quarter tank (nearing the reserve?). Didn't notice it after filling the tank. Thank you for all the information!! I'll try and get my hands on a tac and voltmeter and do a few adjustments.
Sportster-2001-951C-Stock
Well-Known Member
Okay, if I recall on those older skis there's a rubber pickup tube in the bottom of the fuel tank that eventually rots so that might explain why you can't reach quite to the bottom of tank.
If there's something that needs tending in these ALUMINUM carbs that would be the tiny transition ports (aka: "pilot/bypass" holes) in the carburetor bore just upstream of the throttle butterfly. Minor ALUMINUM corrosion in these precision-drilled ports will shift air:fuel ratio to lean side. Consider, factory was already on the edge of lean pleasing the EPA and stretching life of product (2-stroke). Beancounters prefer aluminum over zinc alloy.
Majority of the fuel normally consumed in the engine is delivered through these transition ports.
FWIW, This manual isn't specific to your ski engine, it's general about the series of carburetors. The intent isn't to provide exact calibration detail, just to explain how the carburetor functions and some ideas for what to look for. This actually matches the smaller carbs like yours better than the larger ones, some stuff is kind of misleading when applied to the large 46mm carbs.
http://www.mikuni.com/pdf/sbn_manual.pdf
Adjusting the low speed mixture is for getting the correct ratio at idle speed, if you cannot get engine to idle properly and it seems to be a carburetor issue then have a look inside the low speed mixture passage, likely it's not adjusted correctly or there's some debris in the passage causing lack of fuel control during idle. Of course if fuel tank issues exist the engine won't run well either.
If there's something that needs tending in these ALUMINUM carbs that would be the tiny transition ports (aka: "pilot/bypass" holes) in the carburetor bore just upstream of the throttle butterfly. Minor ALUMINUM corrosion in these precision-drilled ports will shift air:fuel ratio to lean side. Consider, factory was already on the edge of lean pleasing the EPA and stretching life of product (2-stroke). Beancounters prefer aluminum over zinc alloy.
Majority of the fuel normally consumed in the engine is delivered through these transition ports.
FWIW, This manual isn't specific to your ski engine, it's general about the series of carburetors. The intent isn't to provide exact calibration detail, just to explain how the carburetor functions and some ideas for what to look for. This actually matches the smaller carbs like yours better than the larger ones, some stuff is kind of misleading when applied to the large 46mm carbs.
http://www.mikuni.com/pdf/sbn_manual.pdf
Adjusting the low speed mixture is for getting the correct ratio at idle speed, if you cannot get engine to idle properly and it seems to be a carburetor issue then have a look inside the low speed mixture passage, likely it's not adjusted correctly or there's some debris in the passage causing lack of fuel control during idle. Of course if fuel tank issues exist the engine won't run well either.
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