93 SN ran great now poopty, carb rebuilt, then replaced new. Video included.

[750sx1992]

Check your compression, pull your plugs out and check those as well.

Plugs are clean and new, comp is 175/175

 

[750sx1992]

As stated earlier a bad heat sensor will cut spark like that , that is exactly how that circuit works, I noticed the Yellow spark plug wires, what kind of wires are they, are they resistor wires, carbon core or are they solid wires , if they are carbon core you have resistor wires, plugs and caps, resistor means resistance which means loss of spark intensity , resistors cut current or resist current flow, too much resistance and you have serious ignition issues.

My spark plug wires are black with a red sheath. They are copper core as evidenced by the section I cut off when adding new boots. I can try disconnecting the temp sensor all together.

 

[WFO Speedracer]

Disconnect the temp sender and disconnect the stop switch just for testing purposes.

 

[750sx1992]

Disconnect the temp sender and disconnect the stop switch just for testing purposes.

I’ll give both a shot.

 

[WFO Speedracer]

The reason I said check is a guy brought in a 550 one time with total loss, it didn't run right , it had resistor wires, caps and plugs in it, I swapped all of it out for non resistor and the ski ran great, old style total loss didn't have the spark energy to deal with that kind of resistance.

 

[750sx1992]

The reason I said check is a guy brought in a 550 one time with total loss, it didn't run right , it had resistor wires, caps and plugs in it, I swapped all of it out for non resistor and the ski ran great, old style total loss didn't have the spark energy to deal with that kind of resistance.

I’m not running total loss. But now have resister boots and plugs. However adding resister boots didn’t change symptoms. Off tomorrow and will try kill switch and temp sensor.

 

[WFO Speedracer]

I’m not running total loss. But now have resister boots and plugs. However adding resister boots didn’t change symptoms. Off tomorrow and will try kill switch and temp sensor.

You didn't add resistor you changed them, they were resistor boots from the factory, I have replaced many sets of Yamaha boots that had really high resistance which is why I made that suggestion. Have you unplugged the temp sender yet ?

 

[750sx1992]

You didn't add resistor you changed them, they were resistor boots from the factory, I have replaced many sets of Yamaha boots that had really high resistance which is why I made that suggestion. Have you unplugged the temp sender yet ?

I don’t think previous were stock. So maybe resistor maybe not. Negative on temp sensor, I ended up spending Sunday with the wife. I have 2 flights tomorrow, but might be able to try it Tuesday

 

[750sx1992]

You didn't add resistor you changed them, they were resistor boots from the factory, I have replaced many sets of Yamaha boots that had really high resistance which is why I made that suggestion. Have you unplugged the temp sender yet ?

Temp sensor unplugged, no change. Swapped CDI no change. Disconnected white wire from kill switch, no change, except I couldn’t kill it without putting hand over carb.

As for CDI, I guessed it could be the culprit so ordered a cheapo from Amazon for testing. Why not since ebox is open? What’s next, coil?

 

[750sx1992]

Disconnected white with red stripe which I understand is pulser wire. Worse. Primary winding on coil is 1 to 2 ohms. Secondary was 13.5k but measured through 5k boots, making it about 3.5k.

 

[WFO Speedracer]

Do you have a matching stator and flywheel, both either 61x or 62T , Yyou can't mismatch components on those

 

[750sx1992]

Do you have a matching stator and flywheel, both either 61x or 62T , Yyou can't mismatch components on those

I have to assume they match. It’s ran great for years. The CDI I swapped out was labeled 6m6 as was the new one.


I think I finally figured out how to get a reading on the charge coil. Multimeter set on VAC measured from the brown/white stripe to ground in the ebox. 80vac on idle, then the voltage decreased to high 50’s as I revved engine. If I understand it all correctly that voltage should be rising?

 

[750sx1992]

Put a volt meter on the wires to the "charge" coil. Read the AC voltage at idle, then slowly increase throttle. What does the voltage do?

Measured from brown/white stripe to black. 80vac at idle, then decreased to high 50’s as it revved.

Tried a different meter. 50vac at idle, then decreases into 40s as it revs.

It ohmed at 396 before starting it to measure voltage, then around 415ohms after running.

 

[WFO Speedracer]

Ok I had a DR appointment so I had some time to think about your problem, I can't believe it hasn't been mentioned yet but here goes, pull the flywheel off and check for a sheared flywheel key, it will throw the timing off just enough that it will backfire through the carb like that, I had a 550 and a 650 Kawi do the same thing, in both instances the flywheel key was sheared.

Carb issues and ignition issues are sometimes very hard to separate, one will act like the other. Also this would explain it suddenly running badly, all it would take is jumping a wave and not getting off the gas quick enough or backing it in the water with the ski running, in each case the flywheel does what flywheels do which is try to maintain momentum, when the pump hits the water it is like slamming on the brakes, something has to give and that is what the flywheel key is there for.

 

[Myself]

50vac at idle sounds right.....it should INCREASE as you give throttle......the ignition needs more voltage. Either way I would pull the flywheel (checking for a sheared key as WFO suggested) and I would try a known good stator, NOT aftermarket junk. You can buy the charge coil by itself and I've replaced a few on Yamahas through the years.

 

[750sx1992]

Ok I had a DR appointment so I had some time to think about your problem, I can't believe it hasn't been mentioned yet but here goes, pull the flywheel off and check for a sheared flywheel key, it will throw the timing off just enough that it will backfire through the carb like that, I had a 550 and a 650 Kawi do the same thing, in both instances the flywheel key was sheared.

Carb issues and ignition issues are sometimes very hard to separate, one will act like the other. Also this would explain it suddenly running badly, all it would take is jumping a wave and not getting off the gas quick enough or backing it in the water with the ski running, in each case the flywheel does what flywheels do which is try to maintain momentum, when the pump hits the water it is like slamming on the brakes, something has to give and that is what the flywheel key is there for.

I pulled the flywheel just now. Key is in good shape but I discovered something that ain’t right! Found what I can only guess was once part of the starter??? Split in to 3 pieces all caught up in the flywheel.

It also looks like the stator has already been doctored up once.

 

[750sx1992]

50vac at idle sounds right.....it should INCREASE as you give throttle......the ignition needs more voltage. Either way I would pull the flywheel (checking for a sheared key as WFO suggested) and I would try a known good stator, NOT aftermarket junk. You can buy the charge coil by itself and I've replaced a few on Yamahas through the years.

My voltage goes down when reving the engine. As for a good one to test, no suck luck. My other ski is 62t so I can’t borrow it.

 

[WFO Speedracer]

Those are pieces of the starter bendix so thats toast and most likely pieces of it went into the coils on the stator damaging them , I have seen that a lot on Seadoo 951's they eat bendix's like candy, if the voltage isn't increasing I believe that is how the CDI determines the ignition timing curve and that is very possibly your problem , like Myself said it needs more voltage 35VAC is about the minimum voltage at which the ignition will fire .

 

[750sx1992]

Those are pieces of the starter bendix so thats toast and most likely pieces of it went into the coils on the stator damaging them , I have seen that a lot on Seadoo 951's they eat bendix's like candy, if the voltage isn't increasing I believe that is how the CDI determines the ignition timing curve and that is very possibly your problem , like Myself said it needs more voltage 35VAC is about the minimum voltage at which the ignition will fire .

ok, so order a new stator and starter bendix... It appears to have put a slight groove in the flywheel magnets. Think that will be ok? Tell me yes and mean it. If not, I might as well upgrade to 62t while I'm replacing it all for the improved CDI.

 

[WFO Speedracer]

Most likely the flywheel will be ok however there is no reliable way to test a flywheel, probably not exactly what you wanted to hear